Plasmon-enhanced below bandgap photoconductive terahertz generation and detection

Patent metadata

Field	Value
Publication number	US-10680124-B2
Application number	US-201615775709-A
Country	US
Kind code	B2
Filing date	Nov 14, 2016
Priority date	Nov 13, 2015
Publication date	Jun 9, 2020
Grant date	Jun 9, 2020

Abstract

Disclosed are systems and methods for improving applications involving the generation and detection of electromagnetic radiation at terahertz (THz) frequencies. Embodiments of the systems and methods include the fabrication and use of plasmonic devices that enhance light-matter interaction at the nanometer scale by extreme focusing with nanostructured metals. This plasmonic enhancement is used to produce high efficiency THz photoconductive switches that combine the benefits of low-temperature grown GaAs while using mature 1.55 μm femtosecond lasers operating with photon energy below the GaAs band-gap.

First claim

We claim:

1. A terahertz radiation system comprising: a photoconductive switch situated on a semiconductor substrate, the photoconductive switch including a plasmonic resonance structure; and an optical pump source situated to direct a pump beam having photon energy corresponding to about one half of a band gap energy of the semiconductor substrate to the plasmonic resonance structure of the photoconductive switch, wherein the plasmonic resonance structure increases a magnitude of a local field intensity proximate the plasmonic resonance structure produced directly in response to photons of the pump beam.

2. The system of claim 1 , wherein the plasmonic resonance structure includes a one or two dimensional periodic array of conductor portions having a period based on the pump beam photon energy.

3. The system of claim 1 , wherein the photon energy of the pump beam is between 0.4 and 0.6 times the band gap energy of the semiconductor substrate.

4. The system of claim 1 , wherein the plasmonic resonance structure includes an array of conductor portions having a period selected based on a wavelength of the pump beam.

5. The system of claim 4 , wherein the period is selected based on the wavelength of the pump beam in the semiconductor substrate.

6. The system of claim 1 , wherein the period is between 100 nm and 750 nm.

7. The system of claim 1 , wherein the semiconductor substrate comprises a plurality of epitaxially deposited semiconductor layers.

8. The system of claim 1 , wherein the plasmonic resonance structure includes a periodic conductor pattern having a period that is less than a free space wavelength of the pump beam.

9. The system of claim 8 , further comprising a first electrode and a second electrode coupled in series to the periodic conductor pattern of the plasmonic resonance structure so that periodic features of the periodic conductor pattern divide a total voltage between the first electrode and the second electrode so that a portion of the total voltage is applied across each of the periodic features of the periodic pattern.

10. The system of claim 4 , wherein the period is between 100 nm and 1 μm.

11. The system of claim 1 , wherein the plasmonic resonance structure is selected to control reflection of the pump beam.

12. The system of claim 1 , wherein the semiconductor substrate includes a dopant situated proximate the plasmonic resonance structure so as to provide increased pump beam absorption.

13. The system of claim 1 , wherein the optical pump source is a mode-locked laser.

14. The system of claim 1 , wherein the optical pump source comprises first and second continuous-wave lasers, and the optical pump beam includes a first pump beam and a second pump pump associated with the first and second continuous-wave lasers, respectively.

15. The system of claim 1 , wherein the optical pump source is a broadband optical source.

16. A system for generating and receiving terahertz signals, comprising two photoconductive switches defined on at least one semiconductor substrate and situated to receive respective optical pump beams, wherein at least one of the photoconductive switches comprises a plasmonic resonance structure selected based on a wavelength associated with at least a selected one of the optical pump beams so as to increase an associated local field intensity at at least one of the two photoconductive switches directly in response to photons of the selected optical pump beam, wherein the selected optical pump beam has a photon energy corresponding to about one-half of a band gap energy of the at least one semiconductor substrate.

17. The system of claim 16 , further comprising an optical pump source operable to produce the optical pump beams based on splitting of a common optical beam.

18. The system of claim 16 , wherein the two photoconductive switches are optically coupled such that a terahertz signal transmitted from a first photoconductive switch of the two photoconductive switches is received by a second photoconductive switch of the two photoconductive switches.

19. The system of claim 16 , further comprising a sample to be analyzed situated within an optical path between the two photoconductive switches.

20. The system of claim 16 wherein the at least one semiconductor substrate comprises a plurality of epitaxial semiconductor layers.

21. The system of claim 16 , wherein the plasmonic resonance structure includes a periodic nanostructured patterned metal having a period less than a free space wavelength associated with the two optical pump beams.

22. The system of claim 21 , wherein the periods of the periodic nanostructured patterned metal are arranged so that a total voltage across the periodic nanostructured patterned metal is divided across each of the periods.

23. The system of claim 16 , wherein the periodic nanostructured patterned metal is selected so as to control reflection of the optical pump beams, and the semiconductor substrate includes a dopant having a concentration so as increase absorption of the pump beams by the two photoconductive switches.

24. The system of claim 16 further comprising a mode-locked laser, at least two continuous-wave lasers, or at least one broadband optical emission source situated to produce at least one of the optical pump beams.

25. A system for generating or detecting terahertz signals, comprising:
a photoconductive switch that includes a semiconductor substrate and a plasmonic resonance structure defined on the semiconductor substrate, the plasmonic resonance structure including:
a periodic nanostructure-patterned conductor having an array of pattern elements having a pattern period that is less that a free space wavelength of the optical pump beam;
first and second electrical contacts coupled to opposing sides of the periodic nanostructure-patterned conductor such that a voltage at the first and second electrodes is divided by periods of the array of patterns of the periodic nanostructure-patterned conductor; and

an optical pump source situated to direct a pump beam to the periodic nano structure-patterned conductor of the photoconductive switch, the pump beam having a photon energy corresponding to about one-half of a band gap energy of the semiconductor substrate, wherein the periodic nanostructure-patterned conductor is configured to direct the pump beam into the semiconductor substrate and produce an associated electric field proximate the periodic nanostructure-patterned conductor directly in response to photons of the pump beam.

26. The system of claim 25 , wherein each pattern element of the array of pattern elements of the periodic nano structure-patterned conductor extends parallel to a common axis and the first and second electrical contacts are situated so that the voltage applied by the first and seconed electrical contacts is applied along an axis perpendicular to the common axis.

27. A method, comprising:
generating a terahertz signal by directing an optical pump beam to a plasmonic resonance structure on a semiconductor substrate, the optical pump beam having a photon energy corresponding to about one-half of a band gap energy of the semiconductor substrate, wherein the plasmonic resonance structure comprises an array of conductive regions; and
applying a bias voltage across the photoconductive switch, wherein the array divides a voltage applied across the switch between each of the elements of

Assignees

• Uvic Ind Partnerships Inc

Inventors

• Darcie Thomas E
• Gordon Reuven
• Jooshesh Afshin

Classifications

• H01L31/0232 Primary

  Electricity · mapped topic

• H01L31/0304

  Electricity · mapped topic

• H01L27/144

  Electricity · mapped topic

• G01J5/28

  using photoemissive or photovoltaic cells · CPC title

• H01L31/09

  Electricity · mapped topic