ULTRAVIOLET (UV) SCHOTTKY DIODE DETECTOR HAVING SINGLE CRYSTAL UV RADIATION DETECTOR MATERIAL BONDED DIRECTLY TO A SUPPORT STRUCTURE WITH PROPER C-AXIS ORIENTATION
A radiation detector for detecting ultraviolet energy having a single crystal UV radiation detector material and an amorphous support layer disposed directly on the single crystal UV radiation detector material with the single crystal UV radiation detector material having a c-axis aligned along a direction of the ultraviolet energy being detected.
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This disclosure relates generally to ultraviolet (UV) detectors and method for forming such detectors and more particularly to UV detectors and methods for forming such detectors adapted for use in dual band UV and infrared (IR) detectors.
BACKGROUNDAs is known in the art, UV detectors are used in many applications including dual band IR and UV detectors. One method used to produce the Cadmium Sulfide (CdS), in hexagonal form, for such UV detectors, for example, has been to grow bulk CdS material starting with a CdS seed crystal using a vapor phase process as described in a paper entitled “SEEDED GROWTH OF LARGE SINGLE CRYSTALS OF CdS FROM VAPOR PHASE” by G. H. Dierssen and T, Gabor, 1978 published in Journal of Crystal Growth 43 (1978) 572-576. Wafers are sliced from this bulk crystal material, annealed, polished and etched to prepare them for use as Schottky diode UV detector. More particularly, the CdS layer is then cut or sliced into the appropriate thickness by slicing and dicing and then re-annealed in hot sulfur atmosphere to achieve detector electrical properties. In the case of a dual band UV and IR detector, then CdS is then glued to the surface of an infrared filter configured to pass the infrared portion of incident radiation. In the dual band detector, the IR filter is disposed between an upper UV detector and a lower IR detector, as shown in
As is also known in the art, one method used to produce the hexagonal Cadmium Sulfide (CdS) material for IR polarizers, for example, has been to use germanium as a substrate and epitodally grow a relatively thick layer of CdS on the <111> surface of the germanium substrate, as described a paper entitled “Epitaxial Growth of cadmium Sulfide on (111) on germanium (Ge) substrates”: by Paroici et al, in Journal of Material Science, 10 (1975) pages 2117-2123. The formed CdS material grows outwardly perpendicular to the <111>crystallographic plane of the Ge substrate; that is, the c-axis of the grown CdS is perpendicular the <111> surfaces of both the Ge and the gown CdS. The formed CdS is then used as infrared polarizer by positioning the hexagonal crystal c-axis of the formed CdS perpendicular to the Infrared (IR) light to be polarized; see Epitaxial growth of cadmium sulphide on (111) germanium substrates; C. PAORICI, C. PELOSI, G. BOLZON I, G. ZUCCALLI Laboratorio MASPEC-CNR, 43100 Parma, Italy; JOURNAL OF MATERIALS SCIENCE 10 (1975) 2117-2123.
SUMMARYThe inventors have recognized that in order to use the UV radiation detector layer as a UV detector the UV light must be injected parallel to the c-axis and that a new method of epitaxially producing such UV radiation detector layer with proper c-axis orientation relative to the direction of the injected UV light to be detected was required.
In accordance with the present disclosure, a radiation detector for detecting ultraviolet energy is provided. The radiation detector includes: a single crystal UV radiation detector material; and an amorphous support layer disposed directly on the single crystal UV radiation detector material with the single crystal UV radiation detector material having a c-axis aligned along a direction of the ultraviolet energy being detected.
In one embodiment, the amorphous support layer is silicon carbide.
In one embodiment, a Schottky contact metal is provided in Schottky contact with a single crystal UV radiation detector material.
In one embodiment, the single crystal UV radiation detector material is disposed between the amorphous support layer and the Schottky contact metal.
In one embodiment, the amorphous support layer is transparent to infrared radiation.
In one embodiment, a method is provided for forming an UV light detector, comprising: providing a single crystal seed layer having a <111> crystallographic surface; forming an amorphous support layer having a supporting surface perpendicular to the <111> surface; depositing a UV radiation detecting material on both the <111> crystallographic surface of the seed layer and on a portion of the supporting surface adjacent to the single crystal seed layer; and converting the deposited UV radiation detecting material into single crystal UV radiation detecting material with a c-axis thereof perpendicular to the <111> crystallographic axis of the single crystal seed layer.
In one embodiment, the amorphous support layer retards formation of imperfections in the single crystal UV radiation detecting material on the amorphous support layer during the successively heating and cooling.
In one embodiment, a method is provided for forming an UV light detector, comprising: providing a single crystal seed layer having a <111> crystallographic surface; forming an amorphous support layer on a first portion of the <111> surface while exposing a second portion of the <111>0 surface, the amorphous support layer having a supporting surface perpendicular to the <111> surface; depositing a UV radiation detecting material on both the second portion of the <111> crystallogaphic surface of the seed layer and on a portion of the supporting surface adjacent to the a portion of the second portion of the single crystal seed layer; and successively heating and cooling the deposited UV radiation detecting material forming a single crystal layer of the UV radiation detecting material with such UV radiation detecting material being formed to extend outwardly from the second portion of the seed layer, the UV radiation detecting material being learned with a c-axis thereof perpendicular to the <111> crystallographic axis of the single crystal seed layer.
With such structure and method: 1) No bulk crystal growth required. More particularly the use of a bulk crystal is very, very time and process intensive. Cutting and polishing a crystal boule into the detector chips may require as many as 100 steps, any of which could result in a faulty chip or entire run of faulty chips. 2) Thin film CdS significantly improves UV detector performance as recombination noise is reduced. 3) Thin film CdS, as part of a layered IR transmission system, improves integrated IR filter/band pass throughput. 4) An IR transmission system layer acts as UV reflector increasing quantum efficiency of UV detector system.
The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTIONReferring now to
More particularly, referring to
Thus, incident radiation passes onto the upper, surface of the structure with the UV portion of the radiation being detected by the UV detector 10 and the IR radiation passing out of the central portion of the structure to the infrared radiation detector 202 (
Referring now to
Next, the dielectric layer 30L, here silicon dioxide (SiO2) is formed over the lower IR blocking layer 26L and onto the portion of the silicon IR Filter 12 exposed by the aperture 36. Next, the portion of the dielectric layer 30L on the exposed, central portion of the IR filter 12 is removed using any conventional photolithographic-etching process thereby re-exposing the central portion of the bottom of the IR Filter 12 with aperture 36, as shown in
Next, a sequence of three layers of TiO, Al2O3 and MgF making up IR anti-reflection layer 32 (
Next, referring to
Next, referring to
Next, referring to
Next, referring to
Next, referring to FIGS, 11A, 11B and 11C, the layer of the Schottky contact metal 24, here platinum (or other suitable metals or alloys) having a thickness in the example, approximately 5 to 50 nm, preferably 15 nm), is deposited over the surface of the structure, patterned as shown using conventional photolithographic-etching techniques and processing to form a Schottky contact with the semiconductor, UV radiation detector layer 18, as shown.
Next, referring to
Next, referring to
Next, referring to
Next, referring to
Next, referring to
Next, the bond wires 32, 34 are attached to the ohmic contact electrode and Schottky contact electrode 28, as shown in
Referring now to
Next, referring to
Next, after formation of the α-SiC layer 16, the mask 51 of the structure 46 is removed, as shown in
The CVD chamber 50 (
The structure shown in
The heat from the laser beam melts a portion of the deposited CdS at that Ge <111> crystallographic surface (REGION A) and as the beam rotates along an arc, indicated by the curved arrow, the melted portion of the CdS in REGION A solidifies into a single crystal, hexagonal CdS portion, indicated as REGION A′ (
Thus, it is noted that re-melting and re crystallization is done in a single step serially away from the <111> Ge surface to generate a long hexagonal CdS crystal. The re-crystallization of the CdS layer 18 with the pulsed laser is such that the hexagonal CdS layer 18 is grown on the <111> face of the Ge crystal 40 with the c-axis perpendicular to the surface of the CdS layer 18 being formed (that is, parallel to the parallel to a direction of the ultraviolet energy being detected using the re-melting technique discussed in the paper referenced above. This fast pulsed laser method does not over heat the layers around it such as the Ge 40 and glass Layer 14. It is noted that the SiC it is amorphous and won't impact the CdS crystal; it can take the heat of the re-melt step; and it has an index of refraction which matches for that layer position in the stack for the IR “transmission. Thus the amorphous SiC support layer retards formation of imperfections in the single crystal UV radiation detecting material on the amorphous support layer dining the successively heating and cooling.
Next, here the epoxy 42, Ge crystal 40, and any small amount of CdS layer 18 formed on the epoxy 42, as indicated in
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, other Group IV materials may be used in place of Ge, for example silicon wherein the CdS is grown on the <111> face of the silicon. Accordingly, other embodiments are within the scope of the following claims.
Claims
1-6. (canceled)
7. A method for forming an UV light detector, comprising:
- providing a single crystal seed layer having a <111> crystallographic surface;
- providing an amorphous support layer adjacent to the single crystal seed layer; the amorphous support layer having a supporting surface perpendicular to the <111> surface of the single crystal seed layer;
- depositing a UV radiation detecting material on both the supporting surface and on a portion of the <111> crystallographic surface of the single crystal seed layer adjacent to the supporting surface;
- converting the deposited UV radiation detecting material deposited on the supporting surface into single crystal UV radiation detecting material having a c-axis thereof perpendicular to the <111> crystallographic axis of the single crystal seed layer.
8. The method recited in claim 7 wherein the amorphous support layer retards formation of imperfections in the single crystal UV radiation detecting material on the amorphous support layer during successively heating and cooling during the converting.
9. A method for forming an UV light detector, comprising:
- providing a single crystal seed layer having a <111> crystallographic surface;
- providing an amorphous support layer adjacent to the single crystal seed layer, the amorphous support layer having a supporting surface perpendicular to the <111> surface of the single crystal seed layer;
- depositing a UV radiation detecting material on both the supporting surface and on a portion of the <111> crystallographic surface of the single crystal seed layer adjacent to the supporting surface;
- successively heating and cooling the deposited UV radiation detecting material forming a single crystal layer of the UV radiation detecting material on the supporting surface with such UV radiation detecting material on the single crystal seed layer being processed to extend outwardly from the single crystal seed layer to the supporting surface to convert, the UV radiation detecting material on the supporting surface into UV radiation detecting material having a c-axis perpendicular to the supporting surface.
10. The method recited in claim 9 wherein the amorphous support layer retards imperfections in the single crystal UV radiation detecting material on the amorphous support layer during the successively heating and cooling.
11. The method recited in claim 7 the amorphous support layer is silicon carbide.
12. The method recited in claim 7 wherein the UV radiation detector material is Cadmium Sulfide, Cadmium Selenide or Cadmium Telluride.
13. The method recited in claim 7 wherein the amorphous support layer is transparent to infrared radiation.
14. The method recited in claim 13 the amorphous support layer is silicon carbide.
15. The method recited in claim 13 wherein the UV radiation detector material is Cadmium Sulfide, Cadmium Selenide or Cadmium Telluride.
16. The method recited in claim 9 the amorphous support layer is silicon carbide.
17. The method recited in claim 9 wherein the UV radiation detector material is Cadmium Sulfide, Cadmium Selenide or Cadmium Telluride.
18. The method recited in claim 9 wherein the amorphous support layer is transparent to infrared radiation.
19. The method recited in claim 18 the amorphous support layer is silicon carbide.
20. The method recited in claim 18 wherein the UV radiation detector material is Cadmium Sulfide, Cadmium Selenide or Cadmium Telluride.
21. A method for forming a radiation detector, comprising:
- providing a single crystal seed layer having a surface with a predetermined crystallographic orientation;
- providing an amorphous support layer adjacent to the single crystal seed layer, the amorphous support layer having a supporting surface perpendicular to the surface of the single crystal seed layer;
- depositing radiation detecting material on both the supporting surface and on a portion of the surface of the single crystal seed layer adjacent to the supporting surface;
- processing the radiation detecting material on the single crystal seed layer to use the processed radiation detecting material on the single crystal seed layer to convert the deposited radiation detecting material on the supporting surface into single crystal radiation detecting material having a c-axis perpendicular to the supporting surface.
22. A method for forming a radiation detector, comprising:
- providing a single crystal seed layer having a surface having a predetermined crystallographic orientation;
- forming an amorphous support layer, the amorphous support layer having a supporting surface perpendicular to the surface of the single crystal seed layer;
- depositing a radiation detecting material on both the supporting surface and on a portion of the surface of the single crystal seed layer adjacent to the supporting surface;
- processing the radiation detecting material on the single crystal seed layer to use the processed radiation detecting material on the single crystal seed layer to convert the deposited radiation detecting material on the supporting surface into single crystal radiation detecting material having a surface with a crystallographic orientation perpendicular to the crystallographic orientation of the surface of the seed layer.
23. The method recited in claim 7 wherein the processing comprises successively heating and cooling the deposited UV radiation detecting material.
24. The method recited in claim 21 wherein the processing comprises successively heating and cooling the deposited UV radiation detecting material.
25. The method recited in claim 22 wherein the processing comprises
- successively heating and cooling the deposited UV radiation detecting material.
Type: Application
Filed: Sep 28, 2016
Publication Date: Mar 29, 2018
Applicant: Raytheon Company (Waltham, MA)
Inventors: Delmar L. Barker (Tucson, AZ), Jeffrey Clarke (Rio Rico, AZ), Charles W. Hicks (Tucson, AZ)
Application Number: 15/278,656