Solid state radiation detector and process

• US 4,000,502 A
• Filed: 11/05/1973
• Issued: 12/28/1976
• Est. Priority Date: 11/05/1973
• Status: Expired due to Term

• Current Assignee: Hughes Missile Systems Company
• Original Assignee: General Dynamics Corporation
• Inventors: Butler, Jack F., Harnagel, Gary L., Nelson, James R. Jr.
• Primary Examiner(s): Wilbur, Maynard R.
• Assistant Examiner(s): Buczinski, S. C.
• Application Number:
  US05/413,083
• Time in Patent Office: 1,149 Days
• Field of Search: 250/338, 250/370, 250/371, 250/372, 357/15, 357/30, 357/84, 357/68, 357/71, 357/53, 156/17
• US Class Current: 257/453
• CPC Class Codes: H01L 31/02164 for shielding light, e.g. light blocking layers, cold shields for infrared detectors
• CPC Class Codes: H01L 31/07 the potential barriers being only of the Schottky type
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

A radiation detector that combines the characteristics of high quantum efficiency in the UV spectrum with good IR transmission characteristics so that it may be used in association with an IR sensor to produce a coaxial transducer suitable for use in association with unfiltered, high-resolution optics. The detector is a solid state photovoltaic Schottky barrier semi-conductor junction comprising a thin platinum layer laid over single-crystal cadmium sulfide. Processing, including lapping, polishing, and chemical etch, produces a surface suitable for providing radiation sensitivity which drops off sharply outside of the ultraviolet spectrum beyond 550 nanometers. The platinum layer is approximately 35 angstroms in thickness and is therefore transparent both to ultraviolet and infrared radiation. The infrared radiation passes through the cadmium sulfide wafer and through a window in the indium ohmic contact surface on the second surface of the cadmium sulfide crystal. An infrared sensor positioned in association with this window will be exposed to up to 85% of the incident infrared radiation.

Claims

1. A solid state radiation detector utilizing a Schottky barrier in a photovoltaic detector configuration wherein the improvement comprises:

a wafer of crystalline cadmium sulfide having first and second surfaces;

a layer of platinum on said first surface of said wafer, said platinum layer being sufficiently thin to be substantially transparent to ultraviolet radiation, said platinum layer being additionally substantially transparent to infrared radiation;

an insulating layer on said first surface of said wafer, said insulating layer disposed to define an active area of said platinum layer;

a first metallic member superimposed on said insulating layer making contact with said active area of said platinum layer, said first metallic member substantially shielding said wafer from infrared radiation in that area of said wafer outside said active area of said platinum layer;

said second surface of said wafer having an area defining a window substantially directly opposite said active area of platinum layer, said area on said second surface allowing the passage therethrough of infrared radiation; and

a second metallic member making contact with said second surface of said wafer.

2. A solid state radiation detector utilizing a Schottky barrier in a photovoltaic detector configuration wherein the improvement comprises:

a wafer of crystalline cadmium sulfide having first and second surfaces;

a layer of platinum on said first surface of said wafer, said platinum layer being sufficiently thin to be substantially transparent to ultraviolet radiation, said platinum layer being additionally substantially transparent to infrared radiation;

first and second insulating layers on said first surface of said wafer, said insulating layers disposed to define an active area of said platinum layer;

an infrared shield interposed between said first and second insulating layers;

a first metallic member on said first insulating layer making contact with said active area of said platinum layer;

said second surface of said wafer having an area defining a window substantially directly opposite said active area of said platinum layer, said area on said second surface allowing the passage therethrough of infrared radiation; and

a second metallic member making contact with said second surface of said wafer.

3. A process of fabricating a solid state photovoltaic radiation detector comprising the steps of:

removing material from a single crystaline wafer to produce a wafer having two substantially parallel planar surfaces perpendicular to the crystal C-axis;

polishing a first surface of said wafer;

chemically etching said first surface;

depositing a layer of platinum on said surface;

said platinum layer deposited on selected areas of said wafer to produce a matrix of platinum layered areas;

depositing a first layer of permanent photo-resist material surrounding each of said platinum layers;

depositing a copper layer on said first layer of photo-resist;

depositing a second layer of photo-resist over said copper layer and completely insulating said copper layer; and

depositing a copper ring on said second layer of photo-resist and in contact with said platinum layer; and

cutting said wafer into a plurality of elements, each of said elements having a platinum layered area substantially centered thereon.

4. A solid state radiation detector utilizing a Schottky barrier in a photovoltaic detector configuration wherein the improvement comprises:

a wafer of crystaline semiconductor material having a planar top surface;

a layer of platinum on the top surface of said wafer, said platinum layer being sufficiently thin to be substantially transparent to ultraviolet radiation;

contact means for making ohmic contact with said wafer;

said platinum layer extends over a defined area on the top surface of said wafer, and said contact means disposed on the bottom face of said wafer and having an opening aligned with said platinum area.

5. The solid state radiation detector of claim 4, wherein said wafer comprises a single crystal of N-type cadmium sulfide having the crystal c-axis perpendicular to the plane of said top surface.

6. The solid state radiation detector of claim 4, wherein said contact means comprises a metallized layer on the bottom surface of said wafer.

7. A solid state radiation detector of claim 4, wherein said contact means comprises a layer of indium.

8. The solid state radiation detector of claim 4, wherein said platinum layer is contacted through a copper ring, said copper ring shielding a portion of said wafer from infrared radiation.

9. A solid state radiation detector utilizing a Schottky barrier in a photovoltaic detector configuration wherein the improvement comprises:

a wafer of crystaline semiconductor material having a planar top surface;

a layer of platinum on the top surface of said wafer, said platinum layer being sufficiently thin to be substantially transparent to ultraviolet radiation;

contact means for making ohmic contact with said wafer;

and a planar infrared radiation shield comprising a layer of copper surrounding said platinum layer, said infrared shield electrically insulated from said platinum layer and said wafer, said infrared shield lowering the capacitance of said detector.