Atomic layer deposition of lead sulfide for infrared optoelectronic devices

Abstract

A PIN type infrared photodiode including a first electrode, a n-type semiconductor, an atomic layer deposition coating of lead sulfide, a p-type semiconductor and a second electrode, wherein the n-type semiconductor comprises nanowires conformally coated with the atomic layer deposition coating of lead sulfide.

Claims

1. A PIN type infrared photodiode comprising: a first electrode, a n-type semiconductor, an atomic layer deposition coating containing lead sulfide, a p-type semiconductor, and a second electrode, wherein: a content of the lead sulfide in the atomic layer deposition coating is at least 95 wt %, and the n-type semiconductor comprises nanowires conformally coated with the atomic layer deposition coating.

2. The PIN type infrared photodiode according to claim 1, wherein the nanowires comprises zinc oxide.

3. The PIN type infrared photodiode according to claim 1, further comprising a coating of titanium dioxide interposed between the nanowires and the atomic layer deposition coating, the coating of titanium dioxide conformally coating the nanowires.

4. The PIN type infrared photodiode according to claim 1, wherein the p-type semiconductor comprises spiro-MeOTAD.

5. The PIN type infrared photodiode according to claim 1, wherein the first electrode comprises fluorine-doped tin oxide.

6. The PIN type infrared photodiode according to claim 1, wherein the atomic layer deposition coating has a thickness equal to or greater than 5 nm.

7. The PIN type infrared photodiode according to claim 1, wherein the atomic layer deposition coating has a thickness less than or equal to 40 nm.

8. A method for producing a PIN type infrared photodiode, the method comprising: growing nanowires of a n-type semiconductor; and conformally coating the nanowires with lead sulfide by atomic layer deposition to form an atomic layer deposition coating containing lead sulfide, wherein a content of the lead sulfide in the atomic layer deposition coating is at least 95 wt %.

9. The method according to claim 8, further comprising: before the nanowires are conformally coated with lead sulfide, conformally coating the nanowires with titanium dioxide by atomic layer deposition, wherein the nanowires comprise zinc oxide.

10. The method according to claim 8, wherein the nanowires are grown on a fluorine-doped tin oxide substrate.

11. The method according to claim 8, wherein the lead sulfide is deposited from lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) and hydrogen sulfide precursors.

12. The method according to claim 8, wherein a number of cycles for the deposition of the lead sulfide is equal to or greater than 10 cycles.

13. The method according to claim 8, wherein a number of cycles for the deposition of the lead sulfide is less than or equal to 110 cycles.

14. The method according to claim 8, wherein the nanowires are grown from a liquid solution at temperature below 600 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a PIN type infrared photodiode according to embodiments of the present disclosure;

(2) FIG. 2 shows a partial enlargement of FIG. 1;

(3) FIG. 3 shows a graph of the absorption (in %) as a function of the wavelength (in nm) for two different photodiodes;

(4) FIG. 4 shows a graph of the current density (in A.Math.cm.sup.2) as a function of the bias (in V) for two different photodiodes respectively in the dark and under 20 mW.Math.cm.sup.2 at 1530 nm illumination;

(5) FIGS. 5A-5D show the responsivity and specific detectivity at 20 mW.Math.cm.sup.2 illumination for an exemplary photodiode according to embodiments of the disclosure.

DESCRIPTION OF THE EMBODIMENTS

(6) Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

(7) FIG. 1 shows a representation of an exemplary PIN type infrared photodiode 10.

(8) From bottom to top, the PIN type infrared photodiode 10 comprises a glass substrate 12, a first electrode 14, nanowires 16 forming a n-type semiconductor, a p-type semiconductor 18 and a second electrode 20.

(9) In the PIN type infrared photodiode 10 of FIG. 1, the first electrode 14 comprises fluorine-doped tin oxide deposited onto the glass substrate 12. The nanowires 16 were grown onto the first electrode 14. The nanowires 16 may comprise zinc oxide.

(10) Referring to FIG. 2, the nanowires 16 are coated with a conformal coating of titanium dioxide 22 and a conformal coating of lead sulfide 24, the coating of titanium dioxide 22 being sandwich between the nanowires 16 and the coating of lead sulfide 24.

(11) The p-type semiconductor 18 comprises spiro-MeOTAD and the second electrode 20 comprises gold and silver.

(12) The PIN type infrared photodiode 10 is produced by depositing the first electrode 14 on the glass substrate 12 and then growing the nanowires 16 on the first electrode 14.

(13) The nanowires 16 are coated by atomic layer deposition with a conformal coating of lead sulfide 24, i.e., the intrinsic semiconductor. In the example below, before coating the nanowires 16 with a conformal coating of lead sulfide 24, the nanowires 16 are coated by atomic layer deposition with a conformal coating of titanium dioxide 22.

(14) Then the p-type semiconductor 18 is applied onto the conformally coated nanowires 16 and the second electrode 20 is applied.

EXAMPLE

(15) An exemplary PIN type infrared photodiode 10 was produced.

(16) Nanowires 16 were grown on fluorine-doped tin oxide substrate deposited on a glass layer 12.

(17) The seed layer of zinc oxide for the nanowires was deposited by spin-casting of 0.005 M zinc acetate solution on the fluorine-doped tin oxide substrate. The substrate was then annealed for 20 minutes at 400 C.

(18) The growing of the nanowires has taken place in an aqueous solution containing 0.025 M of zinc nitrate hydrate and 0.025 M of hexamethylenetetramine, the substrate being held vertically in the aqueous solution.

(19) The substrate was then dried in air for 4 hours at 60 C.

(20) The substrate carrying the nanowires 16 was subsequently transferred into an atomic layer deposition chamber (Cambridge Nanotech Savannah S100) at 150 C. with a nitrogen carrier gas at a volumetric flow rate of 10 sccm (standard cubic centimetres per minute).

(21) The titanium dioxide coating was deposited starting from tetrakis-dimethyl-amido titanium and water vapour precursors. The pulse duration for the tetrakis-dimethyl-amido titanium was 0.02 second and the pulse duration for the water vapour was 0.015 second. Between each pulse, a purge time of 20 seconds was set.

(22) A cycle for depositing titanium dioxide comprises a first pulse of 0.02 seconds during which tetrakis-dimethyl-amido titanium is introduced into the reaction chamber and is adsorbed onto the surface of the nanowires, a purge of 20 seconds to remove the excess tetrakis-dimethyl-amido titanium, a second pulse of 0.015 seconds during which water vapour is introduced into the reaction chamber and is adsorbed onto the layer of tetrakis-dimethyl-amido titanium and reacts with it to produce titanium dioxide, and finally a purge of 20 seconds to remove the excess water vapour.

(23) In this example, the titanium dioxide coating was deposited by running 20 cycles as described above.

(24) Without breaking the low vacuum in the chamber, the lead sulfide coating was deposited starting from lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) and hydrogen sulfide precursors. The pulse duration for both the lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) and the hydrogen sulfide was 0.5 seconds. Between, each pulse, a purge time of 20 seconds was set.

(25) A cycle for depositing lead sulfide dioxide comprises a first pulse of 0.5 second during which lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) is introduced into the reaction chamber and is adsorbed onto the surface of the titanium dioxide coating, a purge of 20 seconds to remove the excess lead bis(2,2,6,6-tetramethyl-3,5-heptadionate), a second pulse of 0.5 second during which hydrogen sulfide is introduced into the reaction chamber and is adsorbed onto the layer of lead bis(2,2,6,6-tetramethyl-3,5-heptadionate) and reacts with it to produce lead sulfide, and finally a purge of 20 seconds to remove the excess hydrogen sulfide.

(26) In this example, the lead sulfide coating was deposited by running 60 cycles as described above.

(27) The substrate with the coated nanowires was then cooled down at room temperature and transferred to a glovebox.

(28) The p-type semiconductor, i.e., the hole transporting material was formed from spiro-MeOTAD dissolved in chlorobenzene at 63 mg/mL and doped with tert-butylpyridine at 20 L/mL and acetonitrile solution at 70 L/mL containing bis(trifluoromethane)sulfonimide lithium salt at 170 mg/mL.

(29) The solution was spin-casted at 4000 rpm (round per minute) for 60 second in the glovebox containing dry air.

(30) The second electrode was deposited through a shadow mask in an thermal evaporation system (Angstrom Engineering Amod) contained in a glovebox (Innovative Technology). First, a 50 nm thick layer of gold was deposited at a rate of 1.5 .Math.s.sup.1 by ebeam evaporation and a 100 nm thick layer of silver was then deposited at a rate of 1.5 .Math.s.sup.1 by thermal evaporation.

(31) As non-limitative example, the PIN type infrared photodiode 10 is a right circular cylinder having a height of is approximately 1.5 m and a disc surface of approximately 0.07 cm.sup.2 (3 mm in diameter). The thickness of the fluorine-doped tin oxide substrate is approximately 300 nm, the thickness of the spiro-MeOTAD is approximately 200 nm, and the thickness of the second electrode is approximately 150 nm. The thickness of the titanium dioxide coating is approximately 1 nm and the thickness of the lead sulfide coating is approximately 25 nm.

(32) FIG. 3 shows a graph of the absorption (in %) in function of the wavelength (in nm) for two different photodiodes, one without lead sulfide layer (solid line) and one with lead sulfide layer (dashed line). As can be seen, the addition of lead sulfide in the photodiode increases significantly the absorption throughout the infrared and visible range of light.

(33) FIG. 4 shows a graph of the current density (in A.Math.cm.sup.2) in function of the bias (in V) for the photodiode without lead sulfide respectively in the dark (solid line) and under 20 mW.Math.cm.sup.2 at 1530 nm illumination (dotted line) and for the photodiode with lead sulfide respectively in the dark (dashed line) and under 20 mW.Math.cm.sup.2 at 1530 nm illumination (mixed dashed and dotted line). As can be seen, the addition of lead sulfide in the photodiode increases significantly in the reverse-bias current density under illumination, whereas the current-voltage characteristic of the photodiode without lead sulfide remains relatively unchanged.

(34) FIGS. 5A-5D show the responsivity and specific detectivity at 20 mW.Math.cm.sup.2 illumination for a photodiode with lead sulfide. FIG. 5A shows the current (in A) as a function of the time (in ms) of a sample photocurrent transient at 1530 nm and 1 V bias. FIG. 5B shows the responsivity (in A.Math.W.sup.1) as a function of the bias (in V) respectively at 830 nm (solid line) and 1530 nm (dashed line). FIG. 5C shows the internal quantum efficiency (in %) as a function of the bias (in V) respectively at 830 nm (solid line) and 1530 nm (dashed line). FIG. 5D shows the shot-derived specific detectivity10.sup.9 (in Jones) as a function of the bias (in V) respectively at 830 nm (solid line) and 1530 nm (dashed line).

(35) Thus, the photodiode comprising a layer of lead sulfide can be used in many sensing applications. It can be used in applications with a broad spectral response from past 2000 nm down to visible wavelengths. For example, it can be used in receivers for telecommunications at 1500 nm which is a standardized wavelength for almost all telecom technologies. It can also be used in infrared sensing for gesture recognition which often operates in the 850-950 nm range or even in near-field communication devices.

(36) Throughout the description, including the claims, the term comprising a should be understood as being synonymous with comprising at least one unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms substantially and/or approximately and/or generally should be understood to mean falling within such accepted tolerances.

(37) Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

(38) It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.