Silicon-based visible and near-infrared optoelectric devices
In one aspect, the present invention provides a silicon photodetector having a surface layer that is doped with sulfur inclusions with an average concentration in a range of about 0.5 atom percent to about 1.5 atom percent. The surface layer forms a diode junction with an underlying portion of the substrate. A plurality of electrical contacts allow application of a reverse bias voltage to the junction in order to facilitate generation of an electrical signal, e.g., a photocurrent, in response to irradiation of the surface layer. The photodetector exhibits a responsivity greater than about 1 A/W for incident wavelengths in a range of about 250 nm to about 1050 nm, and a responsivity greater than about 0.1 A/W for longer wavelengths, e.g., up to about 3.5 microns.
1. A method for processing a silicon semiconductor substrate, comprising:
irradiating a surface of the silicon substrate with a plurality of circularly polarized short laser pulses so as to generate a plurality of surface structures,
wherein the short laser pulses have a pulse width in a range of about 50 femtoseconds to about 50 picoseconds, a central wavelength in a range of about 200 nm to about 1200 nm, and a fluence in a range of about 1 kJ/m 2 to about 12 kJ/m 2 , and
wherein the plurality of surface structures have a substantially circular base.
2. The method of claim 1 , further comprising exposing one or more locations of said semiconductor surface to a dopant during said step of irradiating the surface.
3. The method of claim 2 , wherein said dopant is an electron-donating dopant.
4. The method of claim 1 , wherein said short laser pulses are applied to said substrate surface at a repetition rate in a range of about 1 kHz to about 1 MHz.
5. The method of claim 1 , wherein the dopant comprises any of sulfur, nitrogen, chlorine, tellurium, and selenium.
6. The method of claim 1 , wherein the fluence is greater than 1 kJ/m 2 .
7. The method of claim 1 , wherein the fluence is greater than 3 kJ/m 2 .
8. The method of claim 1 , wherein the fluence is in a range of 3 kJ/m 2 to about 10 kJ/m 2 .
9. The method of claim 1 , wherein the fluence is in a range of 3 kJ/m 2 to about 8 kJ/m 2 .
10. The method of claim 1 , wherein the fluence is in a range of 1 kJ/m 2 to about 4 kJ/m 2 .
11. The method of claim 1 , wherein the fluence is about 4 kJ/m 2 .
12. The method of claim 1 , wherein the pulse width is in a range of about 50 to about 500 femtoseconds.
13. The method of claim 1 , wherein the pulse width is about 100 femtoseconds.
14. The method of claim 1 , wherein the central wavelength is about 400 nm.
15. The method of claim 1 , wherein the pulses are applied to the substrate surface at a repetition rate in a range to about 50 MHz.
16. The method of claim 2 , wherein the step of exposing comprises depositing the dopant over the silicon surface exposed to laser pulses.
17. The method of claim 2 , wherein the step of exposing comprises depositing the dopant over the irradiated surface of the silicon substrate.