Photoconductive emitter device with plasmonic electrodes

Patent metadata

Field	Value
Publication number	US-9804026-B2
Application number	US-201314372779-A
Country	US
Kind code	B2
Filing date	Jan 23, 2013
Priority date	Jan 23, 2012
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

A photoconductive device that includes a semiconductor substrate, an antenna assembly, and a photoconductive assembly with one or more plasmonic contact electrodes. The photoconductive assembly can be provided with plasmonic contact electrodes that are arranged on the semiconductor substrate in a manner that improves the quantum efficiency of the photoconductive device by plasmonically enhancing the pump absorption into the photo-absorbing regions of semiconductor substrate. In one exemplary embodiment, the photoconductive device is arranged as a photoconductive source and is pumped at telecom pump wavelengths (e.g., 1.0-1.6 μm) and produces milliwatt-range power levels in the terahertz (THz) frequency range.

First claim

The invention claimed is:

1. A photoconductive device for emitting terahertz (THz) radiation, comprising:
a semiconductor substrate;
an antenna assembly fabricated on the semiconductor substrate; and
a photoconductor assembly fabricated on the semiconductor substrate and coupled to the antenna assembly, wherein the photoconductor assembly includes a plurality of plasmonic contact electrodes and wherein the photoconductive device is configured to receive optical input that impinges upon the photoconductor assembly and the plasmonic contact electrodes such that charge carriers are generated in the semiconductor substrate adjacent the plasmonic contact electrodes in response to the impinging optical input;
wherein the plasmonic contact electrodes have sub-wavelength electrode spacing compared to at least one wavelength of the optical input, and wherein the plasmonic contact electrodes are configured to collect the generated charge carriers and are electrically connected to the antenna assembly such that collected charge carriers are conducted to the antenna assembly, whereby the plasmonic contact electrodes provide improved quantum efficiency of the photoconductive device when receiving the optical input.

2. The photoconductive device of claim 1 , wherein the semiconductor substrate includes a first thin layer formed on a second thicker layer, and the photoconductor assembly is fabricated on the first thin layer.

3. The photoconductive device of claim 2 , wherein the first thin layer of the semiconductor substrate includes at least one material selected from the list consisting of: sapphire, silicon (Si), germanium (Ge), silicon germanium (SiGe), indium gallium arsenide (InGaAs), gallium arsenide (GaAs), indium gallium nitride (InGaN), indium phosphide (InP), Graphene or compounds thereof.

4. The photoconductive device of claim 2 , wherein the first thin layer of the semiconductor substrate includes a low-defect thin film with a crystalline structure that is grown on the second thicker layer.

5. The photoconductive device of claim 2 , wherein the first thin layer has a thermal conductivity that is equal to or greater than 0.1 W cm −1 ° C. −1 .

6. The photoconductive device of claim 1 , further comprising a dielectric passivation layer formed on the semiconductor substrate, wherein the dielectric passivation layer encapsulates at least a portion of the plasmonic contact electrodes and enhances optical pump transmission into the semiconductor substrate.

7. The photoconductive device of claim 6 , wherein the dielectric passivation layer includes at least one material selected from the list consisting of: SiN, Si 3 N 4 , or SiO 2 .

8. The photoconductive device of claim 1 , wherein the antenna assembly includes at least one antenna type selected from the list consisting of: a monopole antenna, butterfly antenna, a dipole antenna, a spiral-type antenna, a folded dipole antenna, a log-periodic antenna, or a bow tie-type antenna.

9. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes have a sub-wavelength periodicity, electrode width and electrode spacing that are all less than the wavelength of the optical input.

10. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are arranged so that the intensity of the optical input is concentrated near the plasmonic contact electrodes such that a high concentration of photo-generated electron-hole pairs are located in the immediate vicinity of the plasmonic contact electrodes.

11. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are configured according to at least one shape selected from the list consisting of: a grating, a rectangular-shape, a cross-shape, a C-shape, a H-shape, a split-ring-resonator, a circular hole, or a rectangular hole.

12. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are metallic electrodes and include at least one metal selected from the list consisting of: gold (Au), silver (Ag), titanium (Ti), or nickel (Ni).

13. The photoconductive device of claim 1 , wherein the antenna assembly includes a first antenna terminal coupled to a first lead of an electrical source and a second antenna terminal coupled to a second lead of the electrical source.

14. The photoconductive device of claim 13 , wherein the photoconductor assembly is at least partially located between the first and second antenna terminals.

15. The photoconductive device of claim 14 , wherein the photoconductor assembly includes a first plurality of the plasmonic contact electrodes electrically coupled to the first antenna terminal and a second plurality of the plasmonic contact electrodes electrically coupled to the second antenna terminal.

16. The photoconductive device of claim 15 , wherein each of the first and second pluralities of plasmonic contact electrodes includes plasmonic contact electrodes configured in a periodic array with parallel electrodes that has sub-wavelength periodicity and excites surface plasmon waves.

17. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are integrally formed with the antenna assembly and extend from the antenna assembly.

18. The photoconductive device of claim 1 , wherein the one or more plasmonic contact electrodes are separately formed from the antenna assembly and are connected to the antenna assembly.

19. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are two-dimensional electrodes that have a height dimension that is less than a width or length dimension.

20. The photoconductive device of claim 1 , wherein the plasmonic contact electrodes are three-dimensional electrodes that have a height dimension that is greater than a width or length dimension.

21. The photoconductive device of claim 1 , wherein the photoconductive device is arranged as a terahertz (THz) photoconductive source that is frequency tunable and produces radiation with an output power of at least 1 mW in a frequency range from about 0.1 THz to 10 THz.

22. A method of operating a photoconductive device having a semiconductor substrate that supports both an antenna assembly and a plurality of plasmonic contact electrodes, comprising the steps of:
(a) receiving optical input at the semiconductor substrate;
(b) promoting the excitation of surface plasmon waves or surface waves with the plasmonic contact electrodes, wherein the surface plasmon waves or surface waves influence the optical input so that a greater amount of optical input is absorbed by the semiconductor substrate and results in photocurrent in the semiconductor substrate;
(c) applying a voltage to the antenna assembly so that a first portion of the photocurrent in the semiconductor substrate drifts toward a first antenna terminal and is conducted by at least some of the plasmonic contact electrodes to the first antenna terminal, and so that a second portion of the photocurrent in the semiconductor substrate drifts toward a second antenna terminal and is conducted by at least others of the plasmonic contact electrodes to the second antenna terminal; and
(d) emitting terahertz (THz) radiation from the photoconductive device in response to the first and second antenna terminals being supplied with the first and second portions of photocurrent.

Assignees

• Univ Michigan Regents

Inventors

• Jarrahi Mona
• Berry Christopher W
• Yang Shang-Hua

Classifications

• H01L33/04

  Electricity · mapped topic

• H01L33/38

  Electricity · mapped topic

• H01L31/035209

  Electricity · mapped topic

• H01L31/0224

  Electricity · mapped topic

• G01J3/108 Primary

  for measurement in the infrared range · CPC title