MSM ultraviolet ray receiving element, MSM ultraviolet ray receiving device
10424684 ยท 2019-09-24
Assignee
Inventors
- Akira Yoshikawa (Tokyo, JP)
- Kazuhiro Nagase (Tokyo, JP)
- Motoaki Iwaya (Tokyo, JP)
- Saki USHIDA (Tokyo, JP)
Cpc classification
H01L31/1085
ELECTRICITY
H01L31/02005
ELECTRICITY
H01L31/022408
ELECTRICITY
International classification
H01L29/15
ELECTRICITY
H01L31/112
ELECTRICITY
H01L31/0304
ELECTRICITY
Abstract
An MSM ultraviolet ray receiving element has a low dark state current value and a good photosensitivity. The MSM ultraviolet ray receiving element has a first nitride semiconductor layer on a substrate, a second nitride semiconductor layer on the first nitride semiconductor layer, and first and second electrodes on the second nitride semiconductor layer. The first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.4X0.90). The second nitride semiconductor layer contains Al.sub.YGa.sub.(1-Y)N with a film thickness t (nm) satisfying 5t25. The first electrode and the second electrode contain a material containing at least three elements of Ti, Al, Au, Ni, V, Mo, Hf, Ta, W, Nb, Zn, Ag, Cr, and Zr. Al composition ratios X and Y and a film thickness t satisfy 0.009t+X+0.220.03Y0.009t+X+0.22+0.03.
Claims
1. An MSM ultraviolet ray receiving element comprising: a substrate; a first nitride semiconductor layer formed on the substrate and containing Al.sub.XGa.sub.(1-X)N (0.45X0.90); a second nitride semiconductor layer formed on the first nitride semiconductor layer, containing Al.sub.YGa.sub.(1-Y)N (Y1), and having a film thickness t (nm) satisfying 5t25; and a first electrode and a second electrode formed on the second nitride semiconductor layer and containing a material containing at least three elements of Ti, Al, Au, Ni, V, Mo, Hf, Ta, W, Nb, Zn, Ag, Cr, and Zr, wherein an Al composition ratio X of the first nitride semiconductor layer, and an Al composition ratio Y and a film thickness t of the second nitride semiconductor layer satisfy a following Expression (1);
0.009t+X+0.220.03Y0.009t+X+0.22+0.03(1), and a Schottky junction disposed between the second nitride semiconductor layer and the first and second electrodes, the Schottky junction being configured to disappear when ultraviolet rays are incident on the second nitride semiconductor layer.
2. The MSM ultraviolet ray receiving element according to claim 1, wherein the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.48X0.60).
3. The MSM ultraviolet ray receiving element according to claim 1, wherein the film thickness t of the second nitride semiconductor layer satisfies 10t20.
4. An MSM ultraviolet ray receiving element comprising: a substrate; a first nitride semiconductor layer formed on the substrate and containing Al.sub.XGa.sub.(1-X)N (0.45X0.90); a second nitride semiconductor layer formed on the first nitride semiconductor layer, containing Al.sub.YGa.sub.(1-Y)N (Y1), and having a film thickness t (nm) satisfying 5t25; and a first electrode and a second electrode formed on the second nitride semiconductor layer and containing a material containing at least three elements of Ti, Al, Au, Ni, V, Mo, Hf, Ta, W, Nb, Zn, Ag, Cr, and Zr, wherein an Al composition ratio X of the first nitride semiconductor layer, and an Al composition ratio Y and a film thickness t of the second nitride semiconductor layer satisfy a following Expression (1);
0.009t+X+0.220.03Y0.009t+X+0.22+0.03(1), and the first electrode and the second electrode each include a comb-like portion from a base portion of which a plurality of teeth projects, and the teeth of the first electrode and the teeth of the second electrode are arranged to be alternately adjacent to each other as viewed in plan.
5. The MSM ultraviolet ray receiving element according to claim 1, wherein the first electrode and the second electrode contain at least Al, Mo, and Au.
6. The MSM ultraviolet ray receiving element according to claim 1, wherein a film thickness of the first nitride semiconductor layer is 20 nm or more and 1000 nm or less.
7. An MSM ultraviolet ray receiving element comprising: a substrate; a first nitride semiconductor layer formed on the substrate and containing Al.sub.XGa.sub.(1-X)N (0.45X0.90); a second nitride semiconductor layer formed on the first nitride semiconductor layer, containing Al.sub.YGa.sub.(1-Y)N (Y1), and having a film thickness t (nm) satisfying 5t25; and a first electrode and a second electrode formed on the second nitride semiconductor layer and containing a material containing at least three elements of Ti, Al, Au, Ni, V, Mo, Hf, Ta, W, Nb, Zn, Ag, Cr, and Zr, wherein an Al composition ratio X of the first nitride semiconductor layer, and an Al composition ratio Y and a film thickness t of the second nitride semiconductor layer satisfy a following Expression (1);
0.009t+X+0.220.03Y0.009t+X+0.22+0.03(1), and a two-dimensional electron gas layer with an electron density of 110.sup.11 cm.sup.2 or more and 610.sup.12 cm.sup.2 or less is present on an interface between the first nitride semiconductor layer and the second nitride semiconductor layer.
8. The MSM ultraviolet ray receiving element according to claim 7, wherein a thickness of the two-dimensional electron gas layer is 2 nm or more and 30 nm or less.
9. The MSM ultraviolet ray receiving element according to claim 1, wherein a wavelength (nm) of luminescence caused by photoluminescence and the Al composition ratio X of the first nitride semiconductor layer satisfy a following Expression (2);
1.2410.sup.3/(X.sup.2+1.86X+3.42)101.2410.sup.3/(X.sup.2+1.86X+3.42)+10(2).
10. The MSM ultraviolet ray receiving element according to claim 1, wherein a height of a Schottky barrier in irradiation with ultraviolet rays with a wavelength of 250 nm is 0.1 eV or more and 0.5 eV or less.
11. The MSM ultraviolet ray receiving element according to claim 1, wherein a distance between the first electrode and the second electrode is 1.0 m or more and 30 m or less.
12. The MSM ultraviolet ray receiving element according to claim 1, wherein the substrate is any one of a sapphire substrate, an AlN substrate, and a GaN substrate.
13. The MSM ultraviolet ray receiving element according to claim 1, wherein photosensitivity is 110.sup.5 A/W or more, and a ratio (S/N) of a photocurrent to a dark current is 110.sup.4 or more in irradiation with ultraviolet rays with a wavelength of 250 nm.
14. The MSM ultraviolet ray receiving element according to claim 1, wherein the substrate is an AlN substrate or a sapphire substrate, and absorption coefficient to ultraviolet rays with a wavelength of 265 nm of the substrate is 5 cm.sup.1 or more and 50 cm.sup.1 or less.
15. The MSM ultraviolet ray receiving element according to claim 1, wherein a light reception area is 500 m.sup.2 or more and 15000 m.sup.2 or less.
16. The MSM ultraviolet ray receiving element according to claim 1, wherein a relaxation ratio to the substrate in a (10-12) plane which is an asymmetrical plane of crystal configuring the first nitride semiconductor layer is 0% or more and 5% or less.
17. The MSM ultraviolet ray receiving element according to claim 1, wherein a half value width of an XRD rocking curve in the (10-12) plane which is the asymmetrical plane of the crystal configuring the first nitride semiconductor layer is 50 arcsec or more and 1000 arcsec or less.
18. The MSM ultraviolet ray receiving element according to claim 1, wherein fall time to ultraviolet rays with a wavelength of 250 nm is 0.1 sec or more and 1 msec or less.
19. An MSM ultraviolet ray receiving device comprising: the MSM ultraviolet ray receiving element according to claim 1; and a mounting substrate, wherein the MSM ultraviolet ray receiving element is flip-chip mounted on the mounting substrate.
20. The MSM ultraviolet ray receiving element according to claim 2, wherein the film thickness t of the second nitride semiconductor layer satisfies 10t20.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(12) [Actions and Effects of Ultraviolet Ray Receiving Element of One Aspect]
(13) An MSM ultraviolet ray receiving element which is one aspect of the present invention (hereinafter referred to as ultraviolet ray receiving element of one aspect) can lower the carrier concentration of a two-dimensional electron gas layer on the interface between a first nitride semiconductor layer and a second nitride semiconductor layer in a dark state (state where ultraviolet rays are not incident) to 110.sup.10 cm.sup.3 or less, for example, due to the fact that an Al composition ratio X of the first nitride semiconductor layer, and an Al composition ratio Y and a film thickness t of the second nitride semiconductor layer satisfy Expression (1) above.
(14) When the carrier concentration of the two-dimensional electron gas layer in the dark state is high, a high current value flows between a source and a drain. The current (dark current) flowing in the dark state becomes a noise, which reduces the S/N (photocurrent/dark current) of the light receiving element. The ultraviolet ray receiving element of one aspect reduces the noise by lowering the carrier concentration of the two-dimensional electronic layer in the dark state in such a manner that only a very slight current flows between the source and the drain.
(15) In the ultraviolet ray receiving element of one aspect, the first electrode and the second electrode serving as a source electrode and a drain electrode contain materials containing at least three elements of Ti, Al, Au, Ni, V, Mo, Hf, Ta, W, Nb, Zn, Ag, Cr, and Zr which are materials having low contact resistance. Thus, a Schottky junction is formed between the second nitride semiconductor layer, and the source electrode and the drain electrode, and therefore the current between the source and the drain in the dark state further decreases. On the other hand, when ultraviolet rays are incident on the second nitride semiconductor layer, the carrier concentration of the two-dimensional electron gas layer increases, and thus the Schottky junction between the source electrode and the drain electrode, and the second nitride semiconductor layer disappears. Thus, when light is incident, a photocurrent as high as more than 10.sup.7 A/mm, for example, is obtained.
(16) Thus, the ultraviolet ray receiving element of the present invention achieves both the prevention effect of the dark current (noise) and the increase effect of the photocurrent (signal), and therefore can obtain a very high S/N.
(17) In the ultraviolet ray receiving element of one aspect, the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.45X0.90). By setting the Al composition ratio X of the first nitride semiconductor layer to 0.45 or more and 0.90 or less, the sensitivity to light with a wavelength of 290 nm or more contained in the sunlight or a fluorescent light can be reduced (solar blind).
(18) The description the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.45X0.90) means that most of the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.45X0.90) but the other materials are sometimes contained. For example, the description means that elements other than Al, Ga, and N (for example, dopants, such as Group III elements, such as In, or Mg, Si and the like) are sometimes contained to such an extent (about several percent) that the characteristics of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N (0.45X0.90) are not affected.
(19) In the ultraviolet ray receiving element of one aspect, the second nitride semiconductor layer contains Al.sub.YGa.sub.(1-Y)N (Y1), the film thickness t (nm) satisfies 5t25, and the Al composition ratio Y of the second nitride semiconductor layer satisfies Expression (1). For example, when the Al composition ratio X of the first nitride semiconductor layer is 0.45 and the film thickness t of the second nitride semiconductor layer is 5 nm, the Al composition ratio Y of the second nitride semiconductor layer takes a value of 0.655 or more and 0.715 or less.
(20) The description the second nitride semiconductor layer contains Al.sub.YGa.sub.(1-Y)N means that most of the second nitride semiconductor layers contains Al.sub.YGa.sub.(1-Y)N but the other materials are sometimes contained. For example, the description means that elements other than Al, Ga, and N (for example, dopants, such as Group III elements, such as In, or Mg, Si and the like) are contained to such an extent (about several percent) that the characteristics of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N are not affected. In the ultraviolet ray receiving element of one aspect, ultraviolet rays may be made incident from the side of a substrate or may be made incident from the second nitride semiconductor layer side.
(21) [Supplementary Description about Each Configuration of Ultraviolet Ray Receiving Element of One Aspect]
(22) <Substrate>
(23) The substrate is not particularly limited insofar as the first nitride semiconductor layer can be formed on the substrate. Specifically, Si, SiC, MgO, Ga.sub.2O.sub.3, Al.sub.2O.sub.3, ZnO, GaN, InN, AlN, or a mixed crystal substrate thereof and the like are mentioned as the substrate. Impurities may be mixed in the substrate.
(24) <Method for Confirming Compositions of First and Second Nitride Semiconductor Layers>
(25) (Method for Confirming Elements Contained in First and Second Nitride Semiconductor Layers)
(26) Elements contained in the first and second nitride semiconductor layers can be confirmed by X-ray fluorescence analysis (XRF), Rutherford backscattering spectrometry (RBS), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS).
(27) (Method for Measuring Al Composition Ratio X of Al.sub.XGa.sub.(1-X)N of First Nitride Semiconductor Layer)
(28) The Al composition ratio (X) of Al.sub.XGa.sub.(1-X)N of the first nitride semiconductor layer can be measured by performing 2- scan and reciprocal lattice mapping measurement (RSM) by an X-ray diffraction (XRD) method.
(29) Specifically, first, the 2- scan is performed for the plane of a plane index corresponding to the plane direction of the substrate by the X-ray diffraction, and then the lattice constant of Al.sub.XGa.sub.(1-X)N of the first nitride semiconductor layer is determined from the peak position.
(30) Herein, when the substrate is a substrate cut in a predetermined plane direction with good accuracy (just substrate), the 2- scan can be performed for the plane of a plane index corresponding to the plane direction of the just substrate, and then the lattice constant can be determined from the peak position as described above. When the substrate is a substrate cut giving an off-angle from a predetermined plane direction (off-substrate), the 2- scan needs to be performed by making X-rays incident from an angle shifted corresponding to the off-angle from the surface of the off-substrate.
(31) Next, the X (Al composition ratio) of Al.sub.XGa.sub.(1-X)N is determined from the obtained lattice constant of Al.sub.XGa.sub.(1-X)N using the Vegard's rule. The Vegard's rule is specifically expressed by the following Expression (3);
a.sub.AB=Xa.sub.A+(1X)a.sub.B(3).
(32) In Expression (3), a.sub.A represents the lattice constant of AlN, a.sub.B denotes the lattice constant of GaN, and a.sub.AB denotes the lattice constant of Al.sub.XGa.sub.(1-X)N. Herein, for a.sub.A and a.sub.B, the values (a.sub.A=3.112 , a.sub.B=3.189 ) described in S. Strite and. H. Morko, GaN, AIN, and InN: A review Journal of Vacuum Science & Technology B 10, 1237(1992); doi-ASD: 10.1116/1.585897 are usable.
(33) Therefore, a value of the X (Al composition ratio) can be determined from Expression (3) using a.sub.A=3.112 , a.sub.B=3.189 , and the value (a.sub.AB) of the obtained lattice constant of Al.sub.XGa.sub.(1-X)N.
(34) On the other hand, the relaxation ratio cannot be determined only by the 2- scan, and therefore a correct X (Al composition ratio) cannot be calculated. It is useful to perform the reciprocal lattice mapping in asymmetrical planes, such as a (10-15) plane and a (20-24) plane. Specifically, a point where the 2- peak of the substrate reaches the maximum is measured in the (20-24) plane in which the substrate and the Al.sub.XGa.sub.(1-X)N layer are most separated from each other in the reciprocal lattice space. The 2- is scanned while changing in increments of 0.01 from the point. The process above is repeated, and then the obtained Qx and Qy are mapped, whereby the ratio in which the Al.sub.XGa.sub.(1-X)N layer is relaxed to the substrate can be calculated. Based on the relaxation ratio and the lattice constant calculated above, a correct X (Al composition ratio) can be obtained.
(35) (Method for Measuring Al Composition Ratio Y of Al.sub.YGa.sub.(1-Y)N of Second Nitride Semiconductor Layer)
(36) The Al composition ratio Y of the second nitride semiconductor layer can also be determined by the same method as the method for measuring the Al composition ratio (X) of the first nitride semiconductor layer.
(37) [Preferable Aspect of Ultraviolet Ray Receiving Element of One Aspect]
(38) It is preferable in the ultraviolet ray receiving element of one aspect that the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.48X0.60)
(39) It is preferable in the ultraviolet ray receiving element of one aspect that the film thickness t of the second nitride semiconductor layer satisfies 10t20.
(40) It is preferable in the ultraviolet ray receiving element of one aspect that the first electrode and the second electrode each include a comb-like portion from a base portion of which a plurality of teeth projects and the teeth of the first electrode and the teeth of the second electrode are arranged to be alternately adjacent to each other as viewed in plan.
(41) It is preferable in the ultraviolet ray receiving element of one aspect that the first electrode and the second electrode contain at least Al, Mo, and Au.
(42) It is preferable in the ultraviolet ray receiving element of one aspect that the film thickness of the first nitride semiconductor layer is 20 nm or more and 1000 nm or less.
(43) It is preferable in the ultraviolet ray receiving element of one aspect that a two-dimensional electron gas layer with an electron density of 110.sup.11 cm.sup.2 or more and 610.sup.12 cm.sup.2 or less is present on the interface between the first nitride semiconductor layer and the second nitride semiconductor layer. The thickness of the two-dimensional electron gas layer is preferably 2 nm or more and 30 nm or less.
(44) The thickness and the carrier concentration of the two-dimensional electron gas layer induced on the interface of the nitride semiconductor layer and the second nitride semiconductor layer are determined by the Capacitance-voltage (C-V) measurement.
(45) It is preferable in the ultraviolet ray receiving element of one aspect that the wavelength (nm) of the luminescence caused by photoluminescence and the Al composition ratio X of the first nitride semiconductor layer satisfy the following Expression (2);
1.2410.sup.3/(X.sup.2+1.86X+3.42)101.2410.sup.3/(X.sup.2+1.86X+3.42)+10(2).
(46) In the ultraviolet ray receiving element of one aspect, the Schottky barrier is formed on the interface of metal and the nitride semiconductor by light irradiation. The height (.sub.B) of the Schottky barrier and the saturation current value (I.sub.s) have a relationship given by the following expression (4), and therefore the height (.sub.B) of the Schottky barrier is calculated using Expression (4). A value of the saturation current value (I.sub.s) is defined as a current value of the intercept when an approximation straight line is drawn from a region where the current is saturated.
I.sub.s=SA*T.sup.2exp(.sub.B/kT)(4)
(47) In Expression (4), S indicates the light reception area, A* indicates the Richardson constant, T indicates the absolute temperature, and k indicates Boltzmann constant.
(48) It is preferable in the ultraviolet ray receiving element of one aspect that the height of the Schottky barrier in the irradiation with ultraviolet rays with a wavelength of 250 nm is 0.1 eV or more and 0.5 eV or less.
(49) It is preferable in the ultraviolet ray receiving element of one aspect that the distance between the first electrode and the second electrode is 1.0 m or more and 30 m or less. One of the first electrode and the second electrode serves as the source electrode and the other electrode serves as the drain electrode.
(50) It is preferable in the ultraviolet ray receiving element of one aspect that the distance between the source electrode and the drain electrode (hereinafter referred to as SD distance) is 1.0 m or more and 30 m or less. The source electrode and the drain electrode apply a bias voltage to the ultraviolet ray receiving element, and then extract a current generated by incident light. By setting the SD distance to 1.0 m or more and 30 m or less, a sufficient bias voltage can be applied to the ultraviolet ray receiving element.
(51) The substrate configuring the ultraviolet ray receiving element of one aspect is preferably any one of a sapphire substrate, an AlN substrate, and a GaN substrate. The substrates can grow the first nitride semiconductor layer in the lattice-matched system because a lattice constant difference from the first nitride semiconductor layer is small, and therefore the threading dislocation can be reduced.
(52) It is preferable in the ultraviolet ray receiving element of one aspect that the photosensitivity is 110.sup.5 A/W or more and the ratio (S/N) of the photocurrent to the dark current is 110.sup.4 or more in the irradiation with ultraviolet rays with a wavelength of 250 nm.
(53) The substrate configuring the ultraviolet ray receiving element of one aspect is preferably an AlN substrate or a sapphire substrate and the absorption coefficient to ultraviolet rays with a wavelength of 265 nm of the substrate is 5 cm.sup.1 or more and 50 cm.sup.1 or less.
(54) It is preferable in the ultraviolet ray receiving element of one aspect that the light reception area is 500 m.sup.2 or more and 15000 m.sup.2 or less.
(55) It is preferable in the ultraviolet ray receiving element of one aspect that the relaxation ratio to the substrate in the (10-12) plane which is an asymmetrical plane of crystal configuring the first nitride semiconductor layer is 0% or more and 5% or less.
(56) It is preferable in the ultraviolet ray receiving element of one aspect that the half value width of an XRD rocking curve in the (10-12) plane which is an asymmetrical plane of crystal configuring the first nitride semiconductor layer is 50 arcsec or more and 1000 arcsec or less.
(57) It is preferable in the ultraviolet ray receiving element of one aspect that the fall time (speed of response) in the irradiation with ultraviolet rays with a wavelength of 250 nm is 0.1 sec or more and 1 msec or less.
(58) The speed of response can be confirmed by the following method. In a state where a 3 V constant voltage is applied to the ultraviolet ray receiving element of one aspect, the ultraviolet ray receiving element of one aspect is sufficiently irradiated with ultraviolet rays with a wavelength of 280 nm or less in which the intensity is adjusted to 10 W/cm.sup.2, and then the irradiation with the ultraviolet rays is stopped. The time required for the current value to attenuate by 1/e times a value before stopping the irradiation from the time of stopping the irradiation is measured as the falling time.
(59) It is preferable in the ultraviolet ray receiving element of one aspect that no gate electrode is present on the second nitride semiconductor layer. This makes it possible to eliminate the absorption of ultraviolet rays by the gate electrode, and thus the photosensitivity is improved and element formation processes can be reduced. Herein, the gate electrode means an electrode provided between the source electrode and the drain electrode and having a function of adjusting the carrier concentration of the two-dimensional electron gas layer by the application of a gate voltage, pn junction by doping, or the like.
(60) It is preferable in the ultraviolet ray receiving element of one aspect that the photosensitivity is 110.sup.5 A/W or more and the ratio (S/N) of the photocurrent to the dark current is 110.sup.4 or more when light with a wavelength of 290 nm or less is incident.
(61) It is preferable in the ultraviolet ray receiving element of one aspect that, only when light with a wavelength of 290 nm or less is made incident, a current of 10.sup.7 A/mm or more flows between the source electrode and the drain electrode. Such an ultraviolet ray receiving element has high selectivity of the wavelength of received light.
(62) Furthermore, in the ultraviolet ray receiving element of one aspect, the photosensitivity when light with a wavelength of 290 nm or less is incident is larger by preferably 110.sup.4 A/W or more and more preferably 110.sup.5 A/W or more than the photosensitivity when light with a wavelength of more than 290 nm is incident. Such an ultraviolet ray receiving element has particularly high selectivity of the wavelength of received light.
(63) [Other Descriptions for Ultraviolet Ray Receiving Element of One Aspect]
(64) <First Nitride Semiconductor Layer>
(65) As described above, the film thickness of the first nitride semiconductor layer is preferably 20 nm or more and 1000 nm or less and more preferably 50 nm or more and 900 nm or less.
(66) From the viewpoint of forming the two-dimensional electron gas layer on the interface between the first nitride semiconductor layer and the second nitride semiconductor layer, the first nitride semiconductor layer is preferably undoped. Herein, the undoped means a state where the concentration of impurities is less than 110.sup.16 cm.sup.3. Also when using the wording undoped in the others case, the undoped has the same meaning.
(67) <Second Nitride Semiconductor Layer>
(68) As a method for evaluating the film thickness of the second nitride semiconductor layer, a cross-sectional transmission electron microscope (TEM) is mentioned.
(69) In the ultraviolet ray receiving element of one aspect, the film thickness of the second nitride semiconductor layer is set to 5 m or more and 25 m or less and is preferably 8 nm or more and 20 nm or less and more preferably 10 nm or more and 15 nm or less.
(70) From the viewpoint of securing crystallinity, the second nitride semiconductor layer is preferably undoped.
(71) <Buffer Layer>
(72) The ultraviolet ray receiving element of one aspect may further have a buffer layer between the substrate and the first nitride semiconductor layer. Thus, the crystallinity of the first nitride semiconductor layer is improved, and the photosensitivity can be further increased. As materials of the buffer layer, AlN, AlGaN, and the like are usable.
(73) <First Electrode, Second Electrode>
(74) Materials of the first electrode and the second electrode are particularly preferably alloys containing V, Al, Mo, and Au from the viewpoint of a contact resistance reduction. In this case, as a method for forming the first electrode and the second electrode, a method is mentioned which includes depositing V with a film thickness of 10 nm or more and 30 nm or less, Al with a film thickness of 70 nm or more and 90 nm or less, Mo with a film thickness of 30 nm or more and 50 nm or less, and Au with a film thickness of 40 nm or more and 60 nm or less in this order on the second nitride semiconductor layer, and then performing heat treatment under the conditions of a temperature range of 600 C. or more and 900 C. or less, a temperature rise rate of 7.5 C./sec or more and 20 C./sec or less, and time of 30 seconds or more and 300 seconds or less.
(75) It is also preferable to use Ni with a film thickness of 30 nm or more and 50 nm or less in place of Mo.
(76) <Surface Protective Layer>
(77) The ultraviolet ray receiving element of one aspect may have a surface protective layer. The surface protective layer includes SiO.sub.2, SiN, Al.sub.2O.sub.3, AlN, and the like the surface protective layer is not limited thereto.
(78) <Method for Producing Ultraviolet Ray Receiving Element>
(79) A method for producing the ultraviolet ray receiving element of one aspect includes a process of depositing the first nitride semiconductor layer on the substrate using a metal organic chemical vapor deposition method (MOCVD method), a process of depositing the second nitride semiconductor layer on the first nitride semiconductor layer, and a process of forming the source electrode and the drain electrode on the second nitride semiconductor layer (surface opposite to the first nitride semiconductor layer of the second nitride semiconductor layer).
(80) The first nitride semiconductor layer and the second nitride semiconductor layer can be formed using Al raw materials containing trimethylaluminum (TMAl), for example, Ga raw materials containing trimethylgallium (TMGa), triethylgallium (TEGa), and the like, for example, and N raw materials containing ammonia (NH.sub.3), for example.
(81) A method for forming the first electrode and the second electrode on the second nitride semiconductor layer includes various methods, such as a method including vapor-depositing metal using a resist mask by an electron beam deposition (EB) method.
EMBODIMENT
(82) Hereinafter, an aspect for implementing the present invention (hereinafter referred to as embodiment) is described but the present invention is not limited to the embodiment described below. The embodiment described below is technically preferably limited to implement the present invention but the limitation is not the indispensable requirements of the present invention. The figures are schematically illustrated, and the thickness of each layer is different from the actual thickness and the ratio of each layer is also different from the actual ratio. Specific thickness and dimensions should be determined considering the description of this embodiment or Examples.
(83) As illustrated in
(84) The substrate 2 contains a sapphire substrate. The first nitride semiconductor layer 3 is a layer containing Al.sub.XGa.sub.(1-X)N (0.45X0.60). The film thickness of the first nitride semiconductor layer 3 is 20 nm or more and 1000 nm or less. A buffer layer containing AlN is provided between the substrate 2 and the first nitride semiconductor layer 3. The second nitride semiconductor layer 4 is a layer containing Al.sub.YGa.sub.(1-Y)N and the film thickness t (nm) of the second nitride semiconductor layer 4 is 5 or more and 25 or less.
(85) The Al composition ratio X of the first nitride semiconductor layer 3, and the Al composition ratio Y and the film thickness t of the second nitride semiconductor layer 4 satisfy the following Expression (1);
0.009t+X+0.220.03Y0.009t+X+0.22+0.03(1).
(86) The source electrode 5 and the drain electrode 6 are alloys obtained by heat-treating a laminate in which V, Al, Mo, and Au are deposited in this order from the second nitride semiconductor layer 4 side. An SD distance W (distance between the source electrode 5 and the drain electrode 6) is 1.0 m or more and 30 m or less.
(87) No gate electrode is present on the second nitride semiconductor layer 4.
(88) According to the MSM ultraviolet ray receiving element 1 of the embodiment, the carrier concentration of the two-dimensional electron gas layer on the interface between the first nitride semiconductor layer 3 and the second nitride semiconductor layer 4 in the dark state can be lowered to 110.sup.10 cm.sup.3 or less, for example. When light is incident, a photocurrent as high as more than 10.sup.7 A/mm is obtained, for example. Thus, the MSM ultraviolet ray receiving element 1 of the embodiment can achieve both the prevention effect of the dark current (noise) and the increase effect of the photocurrent (signal), and therefore can obtain a very high S/N.
(89) In the MSM ultraviolet ray receiving element 1 of the embodiment, the source electrode 5 and the drain electrode 6 may have the shape and the arrangement illustrated in
(90) The MSM ultraviolet ray receiving element 1 of the embodiment can be flip-chip mounted on a mounting substrate 7 as illustrated in
EXAMPLES
(91) Hereinafter, Examples and Comparative Examples of the present invention are described.
(92) Ultraviolet ray receiving elements of Examples 1 to 55 and Comparative Examples 1 to 28 have the substrate 2 containing sapphire, the first nitride semiconductor layer 3, the second nitride semiconductor layer 4, the source electrode 5, and the drain electrode 6 and have a buffer layer between the substrate 2 and the first nitride semiconductor layer 3 as with the MSM ultraviolet ray receiving element 1 of the embodiment illustrated in
Example 1
(93) On a substrate containing a 2 inch sapphire wafer, an AlN layer (buffer layer) was grown by 3 m by a metal organic chemical vapor deposition method in a state where the surface temperature of the substrate was maintained at 1250 C. Next, a first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N (X=0.47) was grown by 150 nm on the AlN layer in a state where the surface temperature of the AlN layer was maintained at 1050 C. Next, a second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N (Y=0.65) was grown by 6 nm on the first nitride semiconductor layer 3 in a state where the surface temperature of the first nitride semiconductor layer 3 was maintained at 1050 C.
(94) Next, the substrate of this state was cleaned, and then a resist mask having a plurality of opening portions of 450 m450 m was formed on the second nitride semiconductor layer. Next, mesa isolation was performed using the resist mask and an inductively coupled plasma (ICP) etching device to thereby electrically insulate a plurality of elements formed on the wafer.
(95) Next, the resist mask was removed, and then a laminate forming a source electrode and a drain electrode at an interval of 20 m was formed on the second nitride semiconductor layer by an EB deposition method to each element. Specifically, V, Al, Mo, and Au were deposited in this order from the second nitride semiconductor layer side, and the film thickness of each layer was set as follows: V: 20 nm, Al: 80 nm, Mo: 50 nm, and Au: 40 nm.
(96) Next, the resist mask was removed, and then an annealing process of increasing the temperature to 700 C. in 40 seconds, maintaining the temperature for 30 seconds, and then lowering the temperature using an infrared lamp annealing device was performed. Thus, the source electrode and the drain electrode containing alloys containing V, Al, Mo, and Au were formed.
(97) Next, the sapphire wafer was subjected to dicing, whereby a plurality of ultraviolet ray receiving elements was obtained.
(98) The characteristics of the obtained ultraviolet ray receiving elements were measured by the following methods.
(99) For the measurement of a current (photocurrent) when ultraviolet rays are incident, an artificial sunlight source was used as a light source and a spectroscope was used in combination. Then, the upper surface of the second nitride semiconductor layer was irradiated with ultraviolet light with a wavelength of 250 nm at an intensity of 10 W/cm.sup.2 to measure a current flowing between the source and drain electrodes when the source-drain voltage is set to 3 V. The measurement of a current (dark current) in a dark state where no ultraviolet irradiation was performed was also performed at a source-drain voltage of 3 V. For the current voltage measurement, a parameter analyzer and a probe measuring instrument were used.
(100) As a result of the measurement, the dark current was 1.010.sup.11 A/mm (detection limit) and the photocurrent was 3.010.sup.5 A/mm. The photosensitivity obtained by converting the photocurrent was 310.sup.5 A/W. A ratio (photocurrent/dark current) of the photocurrent value (current value in 250 nm ultraviolet light irradiation) to the obtained dark current value was 3.010.sup.6. The speed of response (fall time) in the ultraviolet light irradiation (when light is incident) was 1 sec or less.
(101) The configurations (Y and t) of the ultraviolet ray receiving element of Example 1 and the measurement results are given in the following Table 1 together with the following Examples 2 to 43.
Examples 2 to 43
(102) Ultraviolet ray receiving elements of Examples 2 to 43 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N, the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N, and the film thickness t to values given in Table 1, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method. The measurement results are also given in Table 1.
(103) TABLE-US-00001 TABLE 1 B18031 Configuration Measurement results t Dark current Photocurrent Photosensitivity X Y (nm) (A/mm) (A/mm) S/N (A/W) Ex. 1 0.47 0.65 6 1.0E11 3.0E05 3.0E+06 3.0E+05 Ex. 2 0.47 0.62 8 1.0E11 7.0E05 7.0E+06 7.0E+05 Ex. 3 0.47 0.61 10 1.0E11 2.0E04 2.0E+07 2.0E+06 Ex. 4 0.47 0.58 12 1.0E11 2.5E04 2.5E+07 2.5E+06 Ex. 5 0.47 0.57 14 1.0E11 1.5E04 1.5E+07 1.5E+06 Ex. 6 0.47 0.55 17 1.0E11 1.0E04 1.0E+07 1.0E+06 Ex. 7 0.47 0.53 18 9.0E10 3.0E04 3.3E+05 3.0E+06 Ex. 8 0.47 0.51 20 2.0E09 7.0E05 3.5E+04 7.0E+05 Ex. 9 0.47 0.50 23 2.0E09 8.0E06 4.0E+03 8.0E+04 Ex. 10 0.52 0.70 6 1.0E11 1.0E05 1.0E+06 1.0E+05 Ex. 11 0.52 0.65 10 1.0E11 6.0E05 6.0E+06 6.0E+05 Ex. 12 0.52 0.63 12 1.0E11 4.0E04 4.0E+07 4.0E+06 Ex. 13 0.52 0.63 14 1.0E11 1.0E04 1.0E+07 1.0E+06 Ex. 14 0.52 0.60 15 1.0E11 3.0E04 3.0E+07 3.0E+06 Ex. 15 0.52 0.59 17 1.0E11 1.0E04 1.0E+07 1.0E+06 Ex. 16 0.52 0.60 18 5.0E10 2.0E04 4.0E+05 2.0E+06 Ex. 17 0.52 0.56 20 7.0E10 9.0E05 1.3E+05 9.0E+05 Ex. 18 0.52 0.55 23 1.0E09 5.0E05 5.0E+04 5.0E+05 Ex. 19 0.57 0.72 7 1.0E11 5.0E06 5.0E+05 5.0E+04 Ex. 20 0.57 0.70 10 1.0E11 2.0E05 2.0E+06 2.0E+05 Ex. 21 0.57 0.67 12 1.0E11 4.0E05 4.0E+06 4.0E+05 Ex. 22 0.57 0.67 14 1.0E11 6.0E05 6.0E+06 6.0E+05 Ex. 23 0.57 0.65 15 1.0E11 8.0E05 8.0E+06 8.0E+05 Ex. 24 0.57 0.62 17 1.0E11 5.0E05 5.0E+06 5.0E+05 Ex. 25 0.57 0.63 18 8.0E11 7.0E05 8.8E+05 7.0E+05 Ex. 26 0.57 0.62 20 3.0E10 3.0E05 1.0E+05 3.0E+05 Ex. 27 0.57 0.60 23 5.0E09 5.0E05 1.0E+04 5.0E+05 Ex. 28 0.65 0.82 6 1.0E11 7.0E06 7.0E+05 7.0E+04 Ex. 29 0.65 0.78 10 1.0E11 1.0E05 1.0E+06 1.0E+05 Ex. 30 0.65 0.75 14 1.0E11 3.0E05 3.0E+06 3.0E+05 Ex. 31 0.65 0.69 20 1.0E11 2.0E05 2.0E+06 2.0E+05 Ex. 32 0.65 0.65 23 1.0E11 8.0E06 8.0E+05 8.0E+04 Ex. 33 0.75 0.90 8 1.0E11 1.0E06 1.0E+05 1.0E+04 Ex. 34 0.75 0.87 12 1.0E11 6.0E06 6.0E+05 6.0E+04 Ex. 35 0.75 0.85 14 1.0E11 1.0E05 1.0E+06 1.0E+05 Ex. 36 0.75 0.80 17 1.0E11 8.0E06 8.0E+05 8.0E+04 Ex. 37 0.75 0.78 23 1.0E11 2.0E06 2.0E+05 2.0E+04 Ex. 38 0.85 0.98 10 1.0E11 1.0E06 1.0E+05 1.0E+04 Ex. 39 0.85 0.96 12 1.0E11 2.0E06 2.0E+05 2.0E+04 Ex. 40 0.85 0.95 14 1.0E11 5.0E06 5.0E+05 5.0E+04 Ex. 41 0.85 0.92 18 1.0E11 3.0E06 3.0E+05 3.0E+04 Ex. 42 0.85 0.89 20 1.0E11 2.0E06 2.0E+05 2.0E+04 Ex. 43 0.85 0.87 23 1.0E11 3.0E07 3.0E+04 3.0E+03 Common points: W = 5 m, Configurations of source and drain electrodes (V-20 nm/Al-80 nm/Mo-50 nm/Au-40 nm)
Comparative Examples 1 to 24
(104) Ultraviolet ray receiving elements of Comparative Examples 1 to 24 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N, the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N, and the film thickness t to values given in Table 2, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method. The measurement results are given in Table 2.
(105) TABLE-US-00002 TABLE 2 B18031 Configuration Measurement results t Dark current Photocurrent Photosensitivity X Y (nm) (A/mm) (A/mm) S/N (A/W) Comp. Ex. 1 0.47 0.66 3 1.0E11 3.0E09 3.0E+02 3.0E+01 Comp. Ex. 2 0.47 0.48 27 1.0E11 6.0E09 6.0E+02 6.0E+01 Comp. Ex. 3 0.47 0.61 15 2.5E06 6.0E04 2.4E+02 6.0E+06 Comp. Ex. 4 0.47 0.50 15 1.0E11 5.5E10 5.5E+01 5.5E+00 Comp. Ex. 5 0.52 0.70 3 1.0E11 1.0E09 1.0E+02 1.0E+01 Comp. Ex. 6 0.52 0.53 27 1.0E11 5.0E09 5.0E+02 5.0E+01 Comp. Ex. 7 0.52 0.66 15 1.0E06 3.0E04 3.0E+02 3.0E+06 Comp. Ex. 8 0.52 0.55 15 1.0E11 2.0E10 2.0E+01 2.0E+00 Comp. Ex. 9 0.57 0.77 3 1.0E11 3.0E10 3.0E+01 3.0E+00 Comp. Ex. 10 0.57 0.60 27 1.0E11 2.0E10 2.0E+01 2.0E+00 Comp. Ex. 11 0.57 0.71 15 8.0E07 2.0E04 2.5E+02 2.0E+06 Comp. Ex. 12 0.57 0.61 14 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 13 0.65 0.85 3 1.0E11 2.0E10 2.0E+01 2.0E+00 Comp. Ex. 14 0.65 0.65 27 1.0E11 2.0E10 2.0E+01 2.0E+00 Comp. Ex. 15 0.65 0.80 15 1.0E06 1.0E04 1.0E+02 1.0E+06 Comp. Ex. 16 0.65 0.65 15 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 17 0.75 0.92 3 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 18 0.75 0.75 27 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 19 0.75 0.75 15 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 20 0.75 0.90 15 1.0E06 8.0E05 8.0E+01 8.0E+05 Comp. Ex. 21 0.85 0.95 5 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 22 0.85 0.85 27 1.0E11 1.0E10 1.0E+01 1.0E+00 Comp. Ex. 23 0.85 1.00 15 1.0E06 6.0E05 6.0E+01 6.0E+05 Comp. Ex. 24 0.85 0.85 15 1.0E11 1.0E10 1.0E+01 1.0E+00 Common points: W = 5 m, Configurations of source and drain electrodes (V-20 nm/Al-80 nm/Mo-50 nm/Au-40 nm)
(106) With respect to Examples 1 to 43 and Comparative Examples 1 to 24, the relationship between the Al composition ratio Y and the film thickness t of the second nitride semiconductor layer was graphed for each Al composition ratio X of the first nitride semiconductor layer.
(107)
(108) Examples 1 to 9 indicated by in
(109)
(110) Examples 10 to 18 indicated by in
(111)
(112) Examples 19 to 27 indicated by O in
(113)
(114) Examples 28 to 32 indicated by in
(115)
(116) Examples 33 to 37 indicated by O in
(117)
(118) Examples 38 to 43 indicated by in
(119) The results above show that, due to the fact that the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.47X0.85) having a thickness of 150 nm, the source and drain electrodes containing V-20 nm/Al-80 nm/Mo-50 nm/Au-40 nm are included, the film thickness t (nm) of the second nitride semiconductor layer satisfies 6t23 (within the range of 5t25), and the Al composition ratio X of the first nitride semiconductor layer, and the Al composition ratio Y and the film thickness t of the second nitride semiconductor layer satisfy Expression (1), the MSM ultraviolet ray receiving elements in which the photosensitivity is 3.010.sup.3 A/W or more and the ratio (S/N) of the photocurrent to the dark current is 410.sup.3 or more when light with a wavelength of 250 nm is incident are obtained.
(120)
(121) It is found from the graphs of
(122) Moreover it is found that, due to the fact that the first nitride semiconductor layer contains Al.sub.XGa.sub.(1-X)N (0.47X0.57) having a thickness of 150 nm, the source and drain electrodes containing V-20 nm/Al-80 nm/Mo-50 nm/Au-40 nm are included, the film thickness t (nm) of the second nitride semiconductor layer satisfies 6t23 (within the range of 5t25), and the Al composition ratio X of the first nitride semiconductor layer, and the Al composition ratio Y and the film thickness t of the second nitride semiconductor layer satisfy Expression (1), the MSM ultraviolet ray receiving elements in which the photosensitivity is 5.010.sup.4 A/W or more and the ratio (S/N) of the photocurrent to the dark current is 410.sup.3 or more when light with a wavelength of 250 nm is incident are obtained.
(123) Moreover, it is found that, in the examples in which the film thickness t of the second nitride semiconductor layer is 8 nm or more and 20 nm or less among the ultraviolet ray receiving elements of Examples 1 to 27 satisfying 0.47X0.57 and in the examples in which the film thickness t of the second nitride semiconductor layer is 10 nm or more and 20 nm or less among the ultraviolet ray receiving elements of Examples 1 to 32 satisfying 0.47X0.65, the photosensitivity is 110.sup.5 A/W or more and the ratio (S/N) of the photocurrent to the dark current has is 110.sup.4 or more when light with a wavelength of 250 nm is incident.
Examples 44 to 46
(124) Ultraviolet ray receiving elements of Examples 44 to 46 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N to 0.52, setting the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N to 0.60, setting the SD distance W to 2 m, 10 m, 25 m, and 20 m, and setting the film thickness t to 15 m, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method.
Comparative Examples 25 and 26
(125) Ultraviolet ray receiving elements of Comparative Examples 25 and 26 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N to 0.52, setting the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N to 0.70, setting the SD distance W to 0.5 m and 35 m, and setting the film thickness t to 3 m, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method.
Examples 47 to 55
(126) Ultraviolet ray receiving elements of Examples 47 to 55 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N to 0.52, setting the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N to 0.60, setting the SD distance W (Distance between the source electrode and the drain electrode) to 20 m, setting the film thickness t to 15 m, and configuring the source and drain electrodes as given in Table 4, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method.
Comparative Examples 27 and 28
(127) Ultraviolet ray receiving elements of Comparative Examples 27 and 28 were created by the same method as that of Example 1, except setting the Al composition ratio X of the first nitride semiconductor layer containing Al.sub.XGa.sub.(1-X)N to 0.52, setting the Al composition ratio Y of the second nitride semiconductor layer containing Al.sub.YGa.sub.(1-Y)N to 0.62, setting the SD distance W to 5 m, setting the film thickness t to 15 m, and configuring the source and drain electrodes as given in Table 4, and then the characteristics of the ultraviolet ray receiving elements were measured by the above-described method.
(128) The configurations and the measurement results of Examples 44 to 55 and Comparative Examples 25 to 28 are given in Tables 3 and 4.
(129) TABLE-US-00003 TABLE 3 B18031 Configurations Measurement results t W Dark current Photocurrent Photosensitivity Y (nm) (m) (A/mm) (A/mm) S/N (A/W) Ex. 44 0.60 15 2 1.0E11 3.0E04 3.0E+07 7.5E+06 Ex. 14 0.60 15 5 1.0E11 3.0E04 3.0E+07 3.0E+06 Ex. 45 0.60 15 10 1.0E11 1.0E04 1.0E+07 5.0E+05 Ex. 46 0.60 15 25 1.0E11 5.0E05 5.0E+06 1.0E+05 Comp. Ex. 25 0.70 3 0.5 Short- Short- N.D. N.D. circuit circuit Comp. Ex. 26 0.70 3 35 1.0E11 2.0E08 2.0E+03 2.9E+01 Common points: X = 0.52, Configurations of source and drain electrodes (V-20 nm/Al-80 nm/Mo-50 nm/Au-40 nm)
(130) TABLE-US-00004 TABLE 4 B18031 Configurations Measurement results Configurations of source W Dark current Photocurrent Photosensitivity Y and drain electrodes (m) (A/mm) (A/mm) S/N (A/W) Ex. 47 0.60 V-20 nm/Al-80 nm/ 20 1.0E11 3.0E06 3.0E+05 7.5E+03 Ni-50 nm/Au-40 nm Ex. 48 0.60 Zr-3 nm/V-20 nm/ 20 1.0E11 8.0E04 8.0E+07 2.0E+06 Al-80 nm/Mo-50 nm/ Au-40 nm Ex. 49 0.60 Zr-3 nm/V-20 nm/ 20 1.0E11 6.0E05 6.0E+06 1.5E+05 Al-80 nm/Ni-50 nm/ Au-40 nm Ex. 50 0.60 Ti-20 nm/Al-80 nm/ 20 1.0E11 8.0E07 8.0E+04 2.0E+03 Mo-50 nm/Au-40 nm Ex. 51 0.60 Nb-20 nm/Al-80 nm/ 20 1.0E11 3.0E04 3.0E+07 7.5E+05 Mo-50 nm/Au-40 nm Ex. 52 0.60 V-20 nm/Al-80 nm/ 20 1.0E11 8.0E04 8.0E+07 2.0E+06 Hf-50 nm/Au-40 nm Ex. 53 0.60 V-20 nm/Al-80 nm/ 20 1.0E11 6.0E04 6.0E+07 1.5E+06 W-50 nm/Au-40 nm Ex. 54 0.60 V-20 nm/Al-80 nm/ 20 1.0E11 7.0E04 7.0E+07 1.8E+06 Ta-50 nm/Au-40 nm Ex. 55 0.60 Ti-20 nm/Al-80 nm/ 20 1.0E11 3.0E07 3.0E+04 7.5E+02 Ni-50 nm/Au-40 nm Comp. 0.62 Ti-20 mn/Au-40 nm 5 1.0E11 1.0E11 1.0E+00 1.0E01 Ex. 27 Comp. 0.62 Ni-20 nm/Au-40 mn 5 1.0E11 1.0E11 1.0E+00 1.0E01 Ex. 28 Common points: X = 0.52, t = 15 nm
(131) Table 3 collectively illustrates Examples 44 to 46 and Comparative Examples 25 and 26 common in the configuration of the source and drain electrodes. Table 3 illustrates Example 14 having the same configuration except the SD distance W. Table 4 collectively illustrates Examples 47 to 55 in which the SD distance W is 20 m and Comparative Examples 27 and 28 in which the SD distance W is 5 m.
(132) The results of Table 3 show the following things. In the case of X=0.52 and Y=0.60, when the SD distance W is 2 m or more and 25 m or less, the photosensitivity can be set to 110.sup.5 A/W or more and the ratio (S/N) of the photocurrent to the dark current can be set to 510.sup.6 or more (110.sup.4 or more) when light with a wavelength of 250 nm is incident. On the other hand, when the SD distance W is 0.5 m, a short-circuit occurs and when the SD distance W exceeds 35 m, the photosensitivity and the ratio (S/N) at a wavelength of 250 nm become extremely small.
(133) The results of Table 4 show the following things. When the source and drain electrodes contain alloys containing four or five metals selected from Ti, Al, Au, Ni, V, Mo, and Zr (Examples 47 to 55), the photosensitivity and the ratio (S/N) at a wavelength of 250 nm are higher than those when the source and drain electrodes contain alloys containing two metals (Comparative Examples 27 and 28).
(134) Moreover, the ultraviolet ray receiving element of Example 49 has the source and drain electrodes of a configuration of further having Zr on the V side of Example 47, and therefore the photosensitivity at a wavelength of 250 nm is 1.510.sup.5 A/W, and thus the photosensitivity remarkably higher than 7.510.sup.3 A/W of Example 47 can be obtained.
(135) Furthermore, when the source and drain electrodes contain alloys containing five metals (Examples 48 and 49) and when any one of Nb, Hf, W and Ta is contained in the alloys configuring the source and drain electrodes (Examples 51 to 54), the photosensitivity at a wavelength of 250 nm can be set to 110.sup.5 A/W or more. 1 MSM ultraviolet ray receiving element 2 substrate 3 first nitride semiconductor layer 4 second nitride semiconductor layer 5 first electrode (source electrode) 51 base portion 52 teeth 6 second electrode (drain electrode) 61 base portion 62 teeth 7 mounting substrate 10 MSM ultraviolet ray receiving device