Device for conducting radiation, a photodetector arrangement, and a method for spatially resolved spectral analysis

Abstract

The invention relates to a device for conducting radiation, a photodetector arrangement, and a method for spatially resolved spectral analysis.

Claims

1. A device for conducting radiation comprising an absorption element, wherein the absorption element has a varying chemical composition along its extension, which composition is characterized by a material gradient in order to vary the energetic position of an absorption edge along the extension of the absorption element, characterized in that the absorption element is arranged on a substrate, wherein a cladding layer is present between the substrate and the absorption element of the substrate is used as a cladding layer.

2. The device according to claim 1, characterized in that the absorption element comprises a higher-energy position of the absorption edge in a front region of the device into which the radiation is introduced than in a rear region, such that during a propagation of the radiation through the device, the radiation increasingly loses high-energy portions and the spectrum shifts toward lower energies.

3. The device according to claim 1, characterized in that the absorption element comprises a material which is a binary, ternary, or quaternary semiconductor alloy.

4. The device according to claim 1, characterized in that the material gradient along the extension of the absorption element is varied in a monotonously rising or falling manner, wherein the material gradient preferably shows a linear or square dependency on the position along the extension of the absorption element.

5. The device according to claim 1, characterized in that the material gradient is formed by varying the proportions of the alloy components of a semiconductor alloy along the extension of the absorption element.

6. The device according to claim 1, characterized in that the absorption element comprises a semiconductor alloy of the general form A.sub.xB.sub.1-x, wherein A and B each represent alloy components and x is the proportion of A in the semiconductor alloy, which is varied along the extension of the absorption element.

7. The device according to claim 1, characterized in that the energy position of the absorption edge along the extension of the absorption element is varied over a spectral region of at least 300 meV, preferably at least 400 meV, at least 500 meV.

8. The device according to claim 1, characterized in that the absorption element is adapted to absorb the radiation along the extension of the device to differing degrees depending on the wavelength of the radiation.

9. The device according to claim 1, characterized in that the absorption element has a length in a range from 50 μm to 20 mm, preferably in a range from 100 μm to 10 mm.

10. The device according to claim 1, characterized in that a material of the absorption element is selected from a group comprising (Mg,Zn)O, (Si,Ge), (Si,Ge)C, (In,Ga).sub.2O.sub.3, (Al,Ga).sub.2O.sub.3, (In,Ga)As, (Al,Ga)As, (In,Ga)N, (Al,Ga)N, (Cd,Zn)O, Zn(O,S), (Al,Ga,In)As, (In, Ga)(As,P), (Al,Ga,In)N, (Mg,Zn,Cd)O, (Al,Ga,In)(As,P), (Al,In,Ga)N, and/or (Al,Ga,In).sub.2O.sub.3.

11. A photodetector arrangement comprising a device according to claim 1, characterized in that a number of N photodetectors are provided along the device, which detectors are in their totality adapted to detect a varying absorption of the radiation by the absorption element along the extension of the device.

12. The photodetector arrangement according to claim 11, characterized in that the photodetector arrangement comprises a data processing device which is adapted to determine the spectrum of the radiation based on the photocurrents measured by the photodetectors.

13. A method for spatially resolved spectral analysis, comprising the following steps: a) provision of a waveguide, wherein the waveguide comprises an absorption element and the absorption element has a varying chemical composition along its extension, which composition is characterized by a material gradient in order to vary the energetic position of an absorption edge along the extension of the absorption element, the absorption element is arranged on a substrate, wherein a cladding layer is present between the substrate and the absorption element of the substrate is used as the cladding layer, b) provision of a radiation, wherein the radiation is coupled into the waveguide, c) absorption of radiation portions by the absorption element depending on the chemical composition of the absorption element and properties of the radiation, wherein charge carriers are released in the absorption element due to the absorption, d) detection of the released charge carriers by a photodetector arrangement, wherein a number of N photodetectors are arranged along the waveguide.

Description

(1) The invention is described with reference to the following figures, wherein:

(2) FIG. 1 shows a schematic cross section through a preferred embodiment of the invention

(3) FIG. 2 shows a schematic top view of a preferred embodiment of the invention

(4) FIG. 3 illustrates an exemplary variation of the spectral position of an absorption edge by means of a variation of the proportions of the alloy components of a semiconductor alloy along the extension of the absorption element

(5) FIG. 1 shows a schematic cross section through a preferred embodiment of the invention (10). Particularly, FIG. 1 shows a waveguide (10), wherein the embodiment of the invention (10) shown in FIG. 1 comprises a substrate (14), a cladding layer (16), and an absorption element (12). The cladding layer (16) can preferably also be called a “cladding.”

(6) FIG. 2 shows a schematic top view of a preferred embodiment of the invention (18). The photodetector (18) comprises a waveguide (10) as well as a series of photodetectors (20) which are arranged on both sides of the waveguide (10). It is preferred for the purpose of the invention that the photodetectors (20) are interconnected, such that their totality forms a photodetector arrangement (18). It is preferred that two photodetectors (20) are arranged opposing each other, wherein a first photodetector (20) of such a photodetector pair can be arranged on the right side of the waveguide (10) and a second photodetector (20) of such a photodetector pair can be arranged on the left side of the waveguide (10). It may also be preferred for the purpose of the invention that a contact of a first photodetector (20) is arranged on the one side of the waveguide (10) and the other contact on the other side of the waveguide (10). It may further be preferred for the purpose of the invention that both contacts of the photodetectors (20) are attached to the same side of the waveguide (10).

(7) It is particularly preferred for the purpose of the invention that the absorption element (12) has a material gradient. The presence of a material gradient means that the chemical composition of the absorption element (12) varies with the extension of the absorption element (12), such that the absorption element (12) has a different chemical composition at different locations. The absorption element (12) preferably comprises a semiconductor alloy having two, three, or four alloy components, wherein the material gradient expresses itself in such a manner that the individual alloy components make up varying proportions of the overall composition at different locations of the absorption element (12). The arrow in FIG. 2 symbolizes in an exemplary manner the incident radiation and the radiation to be analyzed, or its path and/or direction. The three dots in FIG. 2 preferably symbolize that the arrangement of photodetectors (20) continues in this region of the waveguide (10) as well; for the sake of clarity, the respective photodetectors (20) at the two affected sites above and below the waveguide (10) are not shown in FIG. 2, however.

(8) FIG. 3 illustrates a variation of the spectral position of an absorption edge by means of a variation of the proportions of the alloy components of a semiconductor alloy along the extension of the absorption element.

(9) The mode of operation will be described with reference to an example of a (Mg,Zn)O system, wherein the principles explained can be transferred analogously to other semiconductor systems. In the (Mg,Zn)O solid state solution having the chemical formula Mg.sub.XZn.sub.1-XO, x indicates the Mg content.

(10) FIG. 3 shows at the top the experimental absorption spectra for x=0 (that is, pure ZnO), x=0.15 (that is, Mg.sub.0.15Zn.sub.0.85O), and x=0.29 (that is, Mg.sub.0.29Zn.sub.0.71O) and the respective related spectral shift of the band edge.

(11) The spectral position of the absorption edge for x=0 is at about 3.3 eV. The absorption edge for x=0.15 is at ca. 3.6 eV, and the absorption edge for x=0.29 is slightly widened with a spectral position of ca. 3.9-4.1 eV.

(12) As illustrated in the bottom figure, a substantially continuous material gradient from a front region to a rear region is preferably implemented, at which x continuously varies from 0.0 to 0.29.

(13) A material composition with short-wave or higher-energy absorption edge (in this case: high magnesium content; x=0.29) is on the side of the waveguide or absorption element facing the light, while a material composition with a long-wave or low-energy absorption edge (in this case: low magnesium content; x=0.0) is present in the rear region of the waveguide.

(14) While in the front region photons having an energy of ca. 4 eV (wavelength ca. 310 nm) are absorbed, photons having an energy of ca. 3.3 eV (wavelength ca. 375 nm) are absorbed in the rear region. When the light propagates through the device, the radiation thus increasingly loses high-energy portions, such that the spectrum of the radiation shifts towards lower energies.

(15) As described, the varying absorption of the radiation can be detected by means of the photocurrent signal using an arrangement of photodetectors, and a spatially resolved spectral analysis can be carried out.

LIST OF REFERENCE SYMBOLS

(16) 10 Device/waveguide

(17) 12 Absorption element

(18) 14 Substrate

(19) 16 Cladding (layer)

(20) 18 Photodetector arrangement

(21) 20 Photodetector