Silicon-based visible and near-infrared optoelectric devices

• US 20050127401A1
• Filed: 09/24/2004
• Published: 06/16/2005
• Est. Priority Date: 05/25/2001
• Status: Active Grant

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Carey, James E. III, Mazur, Eric
• Granted Patent: US 7,057,256 B2
• Time in Patent Office: Days
• US Class Current: 257/200
• CPC Class Codes: H01L 21/02532 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/02686 Pulsed laser beam
• CPC Class Codes: H01L 21/268 using electromagnetic radiation, e.g. laser radiation
• 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 31/028 including, apart from doping material or other impurities, only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/0288 characterised by the doping material
• CPC Class Codes: H01L 31/036 characterised by their crystalline structure or particular orientation of the crystalline planes
• CPC Class Codes: H01L 31/068 the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
• 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
• CPC Class Codes: Y10S 438/94 Laser ablative material removal

Abstract

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.

Claims

1. A photodetector, comprising:

a silicon substrate having a surface layer doped with sulfur inclusions with an average concentration in a range of about 0.5 to about 5 atom percent so as to exhibit a diodic current-voltage characteristic, said surface layer being configured for exposure to external radiation,

a plurality of electrical contacts disposed on selected portions of the substrate for applying a selected reverse bias voltage to said surface layer to facilitate generation of an electrical signal in response to exposure of the surface layer to radiation,

wherein said surface layer is configured such that generation of said electrical signal in response to said radiation at said reverse bias voltage exhibits a responsivity greater than about 1 amperes/watts (A/W) for at least one wavelength in a range of about 250 nm to about 1050 nm.

2. The photodetector of claim 1, wherein said photodetector exhibits a responsivity greater than about 0.1 amperes/watt for at least one wavelength in range of about 1050 nm to about 3500 nm.

3. The photodetector of claim 1, wherein said photodetector exhibits an average responsivity greater than about 1 A/W for wavelengths in a range of about 250 nm to about 1050 nm.

4. The photodetector of claim 1, wherein said photodetector exhibits a responsivity in a range of about 1 A/W and about 200 A/W for wavelengths in a range of about 250 nm to about 1050 nm.

5. The photodetector of claim 2, wherein said photodetector exhibits an average responsivity greater than about 0.1 A/W for wavelengths in a range of about 1050 nm to about 2000 nm.

6. The photodetector of claim 2, wherein said photodetector exhibits an average responsivity greater than about 0.1 A/W for wavelengths in an range of about 1050 nm to about 3500 nm.

7. The photodetector of claim 1, wherein said doped surface layer has a thickness in a range of about 10 nm to about 1 micron.

8. The photodetector of claim 1, wherein at least two of said electrical contacts are configured for accessing said electrical signal generated in response to said radiation.

9. The photodetector of claim 1, wherein said electrical signal comprises any of a current or a voltage.

10. The photodetector of claim 1, wherein said reverse bias voltage lies in a range of about 0.1 volt to about 15 volts.

11. The photodetector of claim 1, wherein said photodetector exhibits a responsivity in a range of about 1 A/W to about 200 A/W for radiation wavelengths in a range of about 250 nm to about 1100 nm at reverse bias voltages in a range of about 0.1 volts to about 15 volts.

12. The photodetector of claim 1, wherein said silicon substrate comprises a layer formed by a plurality of conical silicon microstructures, said microstructured layer being covered by said sulfur doped layer.

13. The photodetector of claim 1, wherein said sulfur-doped surface layer comprises silicon nanocrystals having diameters in a range of about 10 to about 50 nanometers.

14. The photodetector of claim 12, wherein said conical microstructures having a height in a range of about 0.5 microns to about 30 microns protruding from a surface of said semiconductor to a tip portion having a radius of curvature of about a few hundred nanometers.

15. A photodetector for use in the visible and the infrared regions of the electromagnetic spectrum, comprising:

a crystalline silicon substrate having a microstructured surface layer characterized by a plurality of substantially conical microstructures, said microstructure layer comprising;

a doped layer including a plurality of silicon nanocrystals containing an electron-donating dopant with an average concentration in a range of about 0.5 to about 1.5 atom percent, said microstructured layer exhibiting a diodic current-voltage curve and being configured to receive an external radiation,

a plurality of electrical contacts disposed on selected portions of said substrate for applying a reverse bias voltage said doped layer to facilitate generation of an electrical signal in response to irradiation of at least a portion of said doped layer,

wherein said photodetector exhibits a responsivity greater that about 1 amperes/watt for radiation wavelengths in a range of about 250 nm to about 1050 nm and a responsivity greater than about 0.1 amperes/watt for radiation wavelengths in a range of about 1050 nm to about 3500 nm.

16. The photodetector of claim 15, wherein said photodetector exhibits said responsivities upon application of a reverse bias voltage in a range of about 0.5 V to about 15 V to said microstructured layer.

17. The photodetector of claim 15, wherein said electron-donating constituent comprises any of sulfur, chlorine or nitrogen.

18. A photodetector, comprising:

a silicon substrate having a microstructured layer having inclusions containing an electron-donating constituent adjacent to a bulk silicon portion, said microstructured layer forming a diode junction with an underlying bulk silicon portion,

an electrical contact disposed on a surface portion of said microstructured layer such that at least another surface portion of said layer remains exposed for receiving incident electromagnetic radiation,

another electrical contact disposed on a surface of said bulk silicon portion opposed to said microstructured layer,

wherein upon application of a selected reverse bias voltage to said diode junction via said electrical contacts, said substrate generates a photocurrent in response to exposure of said microstructured layer to incident radiation having wavelengths in a range of about 250 nm to about 1050 nm at a responsivity in a range of about 1 A/W to about 200 A/W.

19. The photodetector of claim 18, wherein said diode junction comprises a p-n junction.

20. The photodetector of claim 18, wherein said silicon substrate generates a photocurrent in response to exposure of said microstructured layer to incident radiation having wavelengths in a range of about 1050 nm to about 2000 nm at a responsivity in a range of about 0.1 A/W to about 100 A/W.

21. The photodetector of claim 18, further comprising a voltage source for applying a bias voltage across said electrical contacts to said silicon substrate.

22. The photodetector of claim 21, wherein said voltage source applies a bias voltage in a range of about −

0.1 to about −

15 V to said substrate.

23. The photodetector of claim 18, wherein said electron-donating constituent comprises sulfur.

24. The photodetector of claim 18, wherein a concentration of said electron-donating constituent in said microstructured layer lies in a range of about 0.5 to about 5 atom percent.

25. The photodetector of claim 24, wherein a concentration of said electron-donating constituent in said microstructured layer lies in a range of about 0.5 to about 1 atom percent.