High gain photoconductive semiconductor switch having tailored doping profile zones

• US 6,248,992 B1
• Filed: 06/18/1999
• Issued: 06/19/2001
• Est. Priority Date: 06/18/1999
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Denison, Gary J., Brown, Darwin J., Zutavern, Fred J, Allerman, Andrew A., Hou, Hong Q., Mar, Alan, Sullivan, Charles T., Zipperian, Thomas E., Baca, Albert G., Helgeson, Wesley D., OʼMalley, Martin W., Loubriel, Guillermo M., Hjalmarson, Harold P.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/336,340
• Time in Patent Office: 732 Days
• Field of Search: 250/214.LS, 250/214.1, 250/214.R, 250/208.1, 250/370.14, 250/370.08, 250/370.01, 250/372, 250/338.4, 257/440-449, 257/430, 257/431, 257/428, 257/336
• US Class Current: 250/214.0LS
• CPC Class Codes: H01L 31/09 Devices sensitive to infrared, visible or ultraviolet radiation H01L31/101 takes precedence

Abstract

A photoconductive semiconductor switch with tailored doping profile zones beneath and extending laterally from the electrical contacts to the device. The zones are of sufficient depth and lateral extent to isolate the contacts from damage caused by the high current filaments that are created in the device when it is turned on. The zones may be formed by etching depressions into the substrate, then conducting epitaxial regrowth in the depressions with material of the desired doping profile. They may be formed by surface epitaxy. They may also be formed by deep diffusion processes. The zones act to reduce the energy density at the contacts by suppressing collective impact ionization and formation of filaments near the contact and by reducing current intensity at the contact through enhanced current spreading within the zones.

Claims

1. A photoconductive semiconductor switch comprising positive and negative electrical contacts located on a semiconductor substrate with the contacts being separated by an intrinsic channel region wherein the contacts are protected from the destructive effects of high current filaments in the channel by respective tailored doping profile zones that separate the contacts from the channel.

2. The switch of claim 1 wherein the zones extend laterally from the edges of the contacts towards the channel and extend into the substrate beneath the contacts.

3. The switch of claim 1 wherein at least one of the zones comprises epitaxial material regrown on the substrate beneath the contacts.

4. The switch of claim 3 wherein the regrowth is in depressions in the surface of the substrate.

5. The switch of claim 3 wherein the regrowth is on the surface of the substrate.

6. The switch of claim 1 wherein the zones comprise a first region of the substrate beneath the positive contact containing a p-dopant and a second region of the substrate beneath the negative contact containing an n-dopant, the vertical profiles of the dopants in the first and second regions extending at least to a depth sufficient to capture a majority of the cross section of a current filament in the channel.

7. A method of forming a photoconductive semiconductor switch comprising:

forming a first tailored doping profile zone of a first conductivity type in the upper surface of a semiconductor substrate;

forming a second tailored doping profile zone of a second conductivity type in the upper surface of the semiconductor substrate, the two zones being separated by a channel region of intrinsic semiconductor material;

forming first and second electrical contacts atop the first and second tailored doping profile zones respectively, such that the depth of the zones is sufficient to capture at least 10% of the cross section of a current filament in the channel and the lateral extent of the zones beyond the perimeter of the contacts is sufficient to protect the electrical contacts from destructive effects of high current filaments in the channel; and

forming bond pad metal atop the first and second contacts.

8. The method of claim 7 wherein at least one of the zones is formed by removing substrate material from the upper surface of the substrate to form a depression in which epitaxial material of the appropriate conductivity type is regrown to form the at least one tailored doping profile zone.

9. The method of claim 8 wherein both zones are formed in the same manner, with one being of the first conductivity type and the other being of the second conductivity type.

10. The method of claim 7 wherein at least one of the zones is formed by diffusing a dopant of a first conductivity type into one of the zones.

11. The method of claim 7 wherein the other zone is formed by diffusing a dopant of a second conductivity type into the other zone.

12. The method of claim 7 wherein at least one of the zones is formed by introducing a dopant of a first conductivity type by ion implantation.

13. A method of forming a photoconductive semiconductor switch comprising:

forming a first tailored doping profile zone of a first conductivity type at the upper surface of a semiconductor substrate;

forming a second tailored doping profile zone of a second conductivity type at the upper surface of the semiconductor substrate, the two zones being separated by a channel region of intrinsic semiconductor material;

forming first and second electrical contacts atop the first and second tailored doping profile zones respectively, such that the depth of the zones and the lateral extent of the zones beyond the perimeter of the contacts are sufficient to protect the electrical contacts from destructive effects of high current filaments in the channel; and

forming bond pad metal atop the first and second contacts.

14. The method of claim 13 wherein at least one of the zones is formed by epitaxial deposition of a doped semiconductor material onto the upper surface of the substrate.

15. The method of claim 14 wherein both zones are formed by epitaxial deposition of respective first and second conductivity type doped semiconductor materials onto the upper surface of the substrate.

16. The method of claim 14 wherein the other of the two zones is formed by diffusion of a dopant of a second conductivity type into the upper surface of the substrate.