Systems and methods for light absorption and field emission using microstructured silicon

• US 7,390,689 B2
• Filed: 05/24/2002
• Issued: 06/24/2008
• Est. Priority Date: 05/25/2001
• Status: Expired due to Term

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Wu, Claudia, Younkin, Rebecca Jane, Carey, James Edward III, Crouch, Catherine H., Mazur, Eric
• Primary Examiner(s): Nguyen; Nam X.
• Assistant Examiner(s): BARTON, JEFFREY THOMAS
• Application Number:
  US10/155,429
• Publication Number:
  US 20030029495A1
• Time in Patent Office: 2,223 Days
• Field of Search: 136/256, 136/251, 136/246, 136/259, 136/261, 257/436, 257/466, 438/69, 438/71, 438/64
• US Class Current: 438/71
• CPC Class Codes: H01L 31/0236 Special surface textures
• CPC Class Codes: H01L 31/02363 of the semiconductor body itself, e.g. textured active layers
• CPC Class Codes: H01L 31/0288 characterised by the doping material
• CPC Class Codes: H01L 31/0543 comprising light concentrating means of the refractive type, e.g. lenses
• CPC Class Codes: H01L 31/0547 comprising light concentrating means of the reflecting type, e.g. parabolic mirrors, concentrators using total internal reflection
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/1864 Annealing
• CPC Class Codes: H01L 31/1872 Recrystallisation
• CPC Class Codes: Y02E 10/52 PV systems with concentrators
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

Methods and systems for absorbing infrared light, and for emitting current are described. A sample, such as a sample containing mainly silicon, is microstructured by at least one laser pulse to produce cone-like structures on the exposed surface. Such microstructuring enhances the infrared absorbing, and current emission properties of the sample.

Claims

1. A method for detecting infrared radiation, the method comprising the steps of:

providing a semiconductor having a plurality of microstructures formed thereon by laser light, the semiconductor possessing a band gap energy, E_bg;

exposing said semiconductor to electromagnetic radiation to allow the sample to absorb a portion thereof, said electromagnetic radiation having a frequency smaller than E_bg divided by Planck'"'"'s constant;

harnessing energy from the absorbed radiation in a photodetector by converting said absorbed radiation having said frequency smaller than E_bg divided by Planck'"'"'s constant into an electrical signal, said signal being indicative of an intensity of said absorbed radiation having a frequency smaller than E_bg divided by Planck'"'"'s constant; and

utilizing said signal to indicate an intensity of the absorbed radiation having a frequency smaller than E_bg divided by Planck'"'"'s constant on a display.

2. The method of claim 1, wherein said step of providing a semiconductor having a plurality of microstructures comprises irradiating a semiconductor surface with a plurality of laser pulses while exposing the surface to a background gas.

3. The method of claim 2, wherein said background gas comprises at least one gas selected from the group consisting of a halogenic gas, nitrogen and air.

4. The method of claim 3, wherein said halogenic gas comprises SF₆.

5. The method of claim 1, wherein said semiconductor comprises silicon.

6. The method of claim 2, wherein said laser pulses have a pulse duration less than about 500 femtoseconds.

7. A method for detecting infrared radiation, the method comprising the steps of:

providing a sample composed of primarily silicon having a plurality of microstructures formed thereon by laser light;

exposing said sample to electromagnetic radiation to allow the sample to absorb a portion thereof, said electromagnetic radiation having one or more wavelengths greater than about 1.05 micrometers, and

utilizing said sample in a photodetector to convert the radiation energy at said one or more wavelengths greater than about 1.05 micrometers to at least one electrical signal, said signal being indicative of an intensity of said absorbed radiation having one or more wavelengths greater than about 1.05 micrometers, and

utilizing said signal to indicate an intensity of the absorbed radiation having one or more wavelengths greater than about 1.05 on a display.

8. The method of claim 7, wherein the step of providing includes providing a sample having a plurality of microstructures formed thereon by exposing said sample to laser light and to a background gas to help form the microstructures.

9. The method of claim 7, wherein the laser light includes a pulse of duration less than about 500 femtoseconds.

10. The method of claim 7, wherein the sample absorbs at least about 50% of the electromagnetic radiation to which the sample is exposed.

11. The method of claim 7, wherein the laser light is produced by a Ti:

sapphire laser producing a wavelength of about 800 nanometers.

12. The method of claim 7, wherein the laser pulse provides a fluence of at least about 2 kJ/m².

13. The method of claim 7, wherein the laser light includes a plurality of laser pulses, each of duration less than about 150 femtoseconds, such that the time interval between each of the plurality of laser pulses is at least about 10⁻

6 seconds.

14. The method of claim 13, wherein the plurality of laser pulses includes at least five laser pulses.

15. The method of claim 8, wherein the background gas is one of nitrogen, air, and a halogenic gas.

16. The method of claim 7, wherein the number density of the microstructures on the sample falls within a range of about 7.5×

10<sup>−

3</sup> to about 4×

10<sup>−

2</sup> per square micrometer.

17. The method of claim 16, wherein an average height of the microstructures is greater than about one micrometer.

18. The method of claim 15, wherein said halogenic gas comprises SF₆.

19. The method of claim 7, wherein the laser light includes a plurality of laser pulses with a duration of about 100 femtoseconds.

20. The method of claim 7, further comprising employing a microprocessor to indicate said signal intensity on the display.

21. A method for photodetection of infrared radiation, comprising

irradiating a silicon substrate surface with a plurality of short laser pulses while exposing said surface to a background gas selected from the group consisting of a halogenic gas, nitrogen and air,

exposing said laser-treated surface in a photodetector to radiation having one or more wavelengths greater than about 1.05 microns to convert the radiation at said one or more wavelengths greater than about 1.05 microns to one or more electrical signals, and

utilizing said signals to indicate intensities of the absorbed radiation having one or more wavelengths greater than about 1.05 on a display.