High-gain photodetector of semiconductor material and manufacturing process thereof

• US 20020185700A1
• Filed: 05/08/2002
• Published: 12/12/2002
• Est. Priority Date: 05/15/2001
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Frisina, Ferruccio, Coffa, Salvatore, Libertino, Sebania
• Granted Patent: US 6,943,390 B2
• Time in Patent Office: Days
• US Class Current: 257/431
• CPC Class Codes: H01L 31/0288 characterised by the doping material
• CPC Class Codes: H01L 31/107 the potential barrier working in avalanche mode, e.g. avalanche photodiodes
• CPC Class Codes: Y02B 10/10 Photovoltaic [PV]
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

The high-gain photodetector is formed in a semiconductor-material body which houses a PN junction and a sensitive region that is doped with rare earths, for example erbium. The PN junction forms an acceleration and gain region separate from the sensitive region. The PN junction is reverse-biased and generates an extensive depletion region accommodating the sensitive region. Thereby, the incident photon having a frequency equal to the absorption frequency of the used rare earth crosses the PN junction, which is transparent to light, can be captured by an erbium ion in the sensitive region, so as to generate a primary electron, which is accelerated towards the PN junction by the electric field present, and can, in turn, generate secondary electrons by impact, according to an avalanche process. Thereby, a single photon can give rise to a cascade of electrons, thus considerably increasing detection efficiency.

Claims

1. A photodetector comprising a semiconductor material body housing a PN junction and a sensitive region that is doped with rare earths, said PN junction configured to form an acceleration and gain region separated from said sensitive region.

2. The photodetector according to claim 1, wherein said PN junction is reverse-biased and generates a depletion region and said sensitive region extends within said depletion region.

3. The photodetector according to claim 1, wherein said semiconductor material is chosen from among silicon, indium phosphide and gallium arsenide.

4. The photodetector according to claim 1, wherein said sensitive region is doped with atoms chosen from the group consisting of erbium, holmium, neodymium and promethium.

5. The photodetector according to claim 1, wherein said semiconductor-material body has a surface, said acceleration and gain region extends contiguously to said surface, and said sensitive region extends beneath said acceleration and gain region.

6. The photodetector according to claim 5, wherein said PN junction is formed by a diode or is formed by a bipolar transistor.

7. The photodetector according to claim 5, wherein said acceleration and gain region and said sensitive region form an active region;

said acceleration and gain region is formed by a surface region, of a first conductivity type and contiguous to said surface, and by a junction region, of a second conductivity type and a first doping level and extending beneath said surface region;

said sensitive region has said second conductivity type and a second doping level, lower than said first doping level; and

wherein said semiconductor-material body, beneath said sensitive region, has said second conductivity type and a third doping level, lower than said second doping level.

8. The photodetector according to claim 7, wherein a separation region having said second conductivity type and said third doping level extends between said junction region and said sensitive region.

9. The photodetector according to claim 7, wherein said semiconductor-material body is formed by a monocrystalline region of a SOI substrate.

10. The photodetector according to claim 9, wherein said active region is formed in a projection of said monocrystalline region, said surface region is contiguous and electrically connected to a first contact region formed on top of said projection, and biasing regions extend in said monocrystalline region, at the sides of said projection, and are in direct electrical contact with second contact regions formed on top of said monocrystalline region.

11. The photodetector according to claim 7, wherein said active region is laterally delimited by trenches, and said semiconductor-material body has a planar structure.

12. The photodetector according to claim 11, wherein said surface region is contiguous and electrically connected to a first contact region formed on top of said surface, and wherein biasing regions extend laterally and externally to said trenches, said biasing regions having said second conductivity type and a fourth doping level, higher than said second doping level, and being connected to second contact regions formed on top of said surface.

13. The photodetector according to claim 11, wherein said trenches are coated or filled with insulating material.

14. The photodetector according to claim 7, wherein said semiconductor-material body has a planar shape, said surface region is contiguous and electrically connected to a first contact region formed on top of said surface, and said active region is formed in a first well having said second conductivity type and said third doping level, said first well being surrounded by a second well having said second conductivity type and a fourth doping level, higher than said second doping level, said second well being contiguous and electrically connected to second contact regions formed on top of said surface.

15. The photodetector according to claim 7, wherein said active region is formed in an epitaxial region having said second conductivity type and said third doping level and overlying a substrate region having said second conductivity type and a fifth doping level, higher than said third doping level, said body having a planar shape, said surface region being contiguous and electrically connected to a first contact region formed on top of said epitaxial region, and second contact regions extending beneath and being contiguous to said substrate region.

17. The process according to claim 16, wherein said sensitive region is doped with atoms chosen from the group comprising erbium, holmium, neodymium, and promethium.

18. The process according to claim 16, comprising the steps of:

forming a surface region, having a first conductivity type, in a semiconductor-material body having a second conductivity type;

forming a junction region, having said second conductivity type and a first doping level, in said semiconductor-material body beneath said surface region; and

forming said sensitive regions having said second conductivity type and a second doping level, lower than said first doping level, in said semiconductor-material body beneath said junction region,

said semiconductor-material body having said second conductivity type and a third doping level, lower than said second doping level.

19. The process according to claim 18, wherein said step of forming a surface region comprises implanting boron ions at an energy of 5-50 keV and a dose of 1×

10¹⁴-1×

10¹⁶ atoms/cm² so as to obtain a final doping level of 1×

10¹⁹-1×

10²⁰ atoms/cm³ and a depth of 0.1-0.15 μ

m;

said step of forming a junction comprises implanting phosphorus ions or arsenic ions at an energy of 80-150 keV and a dose of 1×

10¹⁴-1×

10¹⁶ atoms/cm² so as to obtain a final doping level of 1×

10¹⁹-1×

10²⁰ atoms/cm³ and a depth of 0.15-0.2 μ

m; and

said step of forming a sensitive region comprises implanting ions of rare earths at an energy of 0.5-2.5 MeV at doses of 1×

10¹²-1×

10¹⁴ atoms/cm² so as to obtain a peak final concentration of 1×

10¹⁶-1×

10¹⁸ atoms/cm³.

20. The process according to claim 16, further comprising the step of forming trenches at the sides of said PN junction and said sensitive region.

16. A process for manufacturing a photodetector, comprising the steps of:

forming a PN junction in a semiconductor-material body; and

forming a sensitive region doped with rare earths in said semiconductor-material body,

said sensitive region being formed separately from said PN junction.

21. A method for detecting light, the method comprising:

exposing a sensitive region having rare earth ions to the light;

capturing photons of the light with the rare earth ions to generate primary electrons within the sensitive region; and

accelerating the primary electrons by an electric field to pass through a gain region to generate secondary electrons by an avalanche process.

22. The method of claim 21, wherein accelerating the primary electrons and generating the secondary electrons occurs in a PN junction.

23. The method of claim 21, wherein accelerating the primary electrons and generating the second electrons occurs in one of the following:

a diode and bi-polar transistor.

24. The method of claim 21, wherein the rare earth ions comprise one of the following:

erbium, holmium, neodymium, and promethium.

25. A system for detecting light, the system comprising:

means for exposing rare earth ions to the light to generate primary electrons;

means for accelerating the primary electrons; and

means for generating secondary electrons from the accelerated primary electrons through an avalanche process.