US2868736A - Preparation of photosensitive crystals - Google Patents
Preparation of photosensitive crystals Download PDFInfo
- Publication number
- US2868736A US2868736A US541147A US54114755A US2868736A US 2868736 A US2868736 A US 2868736A US 541147 A US541147 A US 541147A US 54114755 A US54114755 A US 54114755A US 2868736 A US2868736 A US 2868736A
- Authority
- US
- United States
- Prior art keywords
- crystals
- cadmium selenide
- plate
- metal
- molybdenum
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
- 239000013078 crystal Substances 0.000 title claims description 15
- 238000002360 preparation method Methods 0.000 title description 2
- 238000000034 method Methods 0.000 claims description 20
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 claims description 18
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 15
- 229910052750 molybdenum Inorganic materials 0.000 claims description 15
- 239000011733 molybdenum Substances 0.000 claims description 15
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 10
- 239000001301 oxygen Substances 0.000 claims description 10
- 229910052760 oxygen Inorganic materials 0.000 claims description 10
- 230000008016 vaporization Effects 0.000 claims description 7
- 238000000151 deposition Methods 0.000 claims description 5
- 230000002708 enhancing effect Effects 0.000 claims description 5
- 229910052751 metal Inorganic materials 0.000 description 18
- 239000002184 metal Substances 0.000 description 18
- 239000007858 starting material Substances 0.000 description 13
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 12
- 239000012190 activator Substances 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 206010034972 Photosensitivity reaction Diseases 0.000 description 6
- 230000036211 photosensitivity Effects 0.000 description 6
- 229910052697 platinum Inorganic materials 0.000 description 6
- 229910052715 tantalum Inorganic materials 0.000 description 5
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 5
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 4
- ZJRXSAYFZMGQFP-UHFFFAOYSA-N barium peroxide Chemical compound [Ba+2].[O-][O-] ZJRXSAYFZMGQFP-UHFFFAOYSA-N 0.000 description 4
- 150000001875 compounds Chemical class 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 229910052709 silver Inorganic materials 0.000 description 4
- 239000004332 silver Substances 0.000 description 4
- 229910052716 thallium Inorganic materials 0.000 description 4
- BKVIYDNLLOSFOA-UHFFFAOYSA-N thallium Chemical compound [Tl] BKVIYDNLLOSFOA-UHFFFAOYSA-N 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- 229910052797 bismuth Inorganic materials 0.000 description 3
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 3
- 229910052793 cadmium Inorganic materials 0.000 description 3
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 3
- 239000002178 crystalline material Substances 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 239000010453 quartz Substances 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- 150000004772 tellurides Chemical class 0.000 description 3
- 229910052718 tin Inorganic materials 0.000 description 3
- 229910052787 antimony Inorganic materials 0.000 description 2
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 2
- 150000003346 selenoethers Chemical class 0.000 description 2
- 238000009834 vaporization Methods 0.000 description 2
- 239000011364 vaporized material Substances 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/88—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
Definitions
- the present invention relates to photosensitive compounds of thetype that increase in electrical conductivity when subjected to light rays and comprises a novel method for preparing photosensitive compounds of cadmium or the like that is adapted for practice on a commercial scale and results in a product of substantially uniform electrical characteristics and of relatively high photosensitivity.
- the process' is applicable to starting compounds which have little or no initial photosensitivity.
- suitable starting materials are suliides, selenides and tellurides of cadmium, indium, thallium, tin, lead, antimony and bismuth and combinations thereof, such as sullides and tellurides of silver and thallium combined with silver, bismuth, tin or thallium. It is not necessary that the starting material be chemically pure. In fact superior results have been obtained when the starting material contains traces of impurities such as are to be expected in commercial products.
- the invention is directed primarily to the process whereby photosensitivity is enhanced in materials of the above type and not to any new chemical compound.
- cadmium selenide is specified as the starting material. It will ⁇ be understood that the process is equally applicable to other materials such as above indicated.
- the process of the invention comprises vaporization of the starting material under vacuum and condensation upon a metal wall in which, or on the surface of which, is the activator for enhancement of the photosensitivity of the deposited crystalline material.
- the activator preferably oxygen
- the metal may contain occluded oxygen, or the metal may be oxidized or may be coated with an oxide of another material.
- the activated crystalline material deposited upon the metal wall is readily removable by mechanical means and is suitable for use in manufacture of photoelectric cells.
- the starting material 2 for example, commercial cadmium selenide containing traces of impurities, is placed in a quartz container 4 having a loose fitting lid 6 of tantalum, kmolybdenum or other metal of high melting point containing or carrying an activator for the material to be deposited thereon.
- a lid of oxidized molybdenum has been found particularly satisfactory in the process.
- the container 4 with its contents andthe lid 6 is placed 2 within a platinum cylinder 8 about the lower end of which is a coil 10 to which radio frequency current is delivered through leads 12.
- a cooling coil 14' is positioned about the lid 6 and temperature-responsive means as, for example, a thermocouple indicated diagrammatically at 16 is provided for control of the temperature of the lid.
- a chamber 18 adapted to be evacuated as by a connection, diagrammatically indicated at 20, to a vacuum system.
- the chamber 18 is maintained at a pressure of about l06 mm. and the temperature of the starting material raised by radio frequency induction heating to about 900 C.
- the coil surrounds the lower portion only of the platinum cylinder and as the lid 6 is maintained at a lower temperature by means of the cooling coil 14 there will be a temperature differential maintained between the starting material in theV bottom of the yquartz container and the metal-lid 6.
- Heating is maintained for about thirty minutes after which time the inside surface of the lid 6 will be found covered with a coating of crystals which sticks to the metal lid and may, after cooling, be removed mechanically.
- a quartz cylinder of about 1/2" diameter and a height of 1" one run will form suicient deposit from which up to fty small photosensitive cells can be made.
- the metal lid 6, instead of being oxidized, may be coated with a thin layer of barium peroxide or with a thin layer containing an activator other than oxygen.
- Photosensitivity of crystals of cadmium selenide deposited on oxidized molybdenum with 22.5 volts across an electrode spacing of about l mm. and illumination of 270 microwatts per square centimeter in the region of maximum spectral response ( ⁇ .750;i) averaged over amperes per watt for four samples.
- the method of enhancing photoconductivity in crystalline material which comprises vaporizing the material under vacuumand depositing the vaporized material on a metal: plate carrying oxygen as an activator, said material being selected from the group consisting of suldes, selenides and tellurides of cadmium, indium, thallium, tin, silver, lead, antimony and bismuth and combinations thereof.
- the method of enhancing the photoconductivity of cadmium selenide which comprises vaporizing crystals of cadmium selenide under vacuum and depositing the vaporized cadmium selenide on an oxide coated plate of tantalum.
- the method of enhancing photoconductivity of cadmium selenide which comprises vaporizing crystals of cadmium selenide under vacuum and depositing the vaporized cadmium selenide on a plate of molybdenum carrying occluded oxygen.
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- General Physics & Mathematics (AREA)
- Manufacturing & Machinery (AREA)
- Computer Hardware Design (AREA)
- Physics & Mathematics (AREA)
- Power Engineering (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
- Light Receiving Elements (AREA)
Description
Jan. 13, 1959 v QwElNRl-:ICH 2,868,736
PREPARATIQN oF PHoToYsENsITIvE CRYSTALS Fild oct. l18. 1955 AT TO R N EY 2,868,736 Patented Jan. 13,v 1959 2,s6s,1s6 PREPARATION oF PHoTosENsmvE CRYSTALS Otto Weinreich, East Orange, N. J., assignor to Tung-Sol Electric Inc., a corporation of Delaware Application October 18, 1955, Serial No. 541,147
Claims. c (Cl. 252-501) The present invention relates to photosensitive compounds of thetype that increase in electrical conductivity when subjected to light rays and comprises a novel method for preparing photosensitive compounds of cadmium or the like that is adapted for practice on a commercial scale and results in a product of substantially uniform electrical characteristics and of relatively high photosensitivity.
The process' is applicable to starting compounds which have little or no initial photosensitivity. Examples of suitable starting materials are suliides, selenides and tellurides of cadmium, indium, thallium, tin, lead, antimony and bismuth and combinations thereof, such as sullides and tellurides of silver and thallium combined with silver, bismuth, tin or thallium. It is not necessary that the starting material be chemically pure. In fact superior results have been obtained when the starting material contains traces of impurities such as are to be expected in commercial products. The invention is directed primarily to the process whereby photosensitivity is enhanced in materials of the above type and not to any new chemical compound.
For convenience in the following description of the process of the invention, cadmium selenide is specified as the starting material. It will `be understood that the process is equally applicable to other materials such as above indicated.
In general the process of the invention comprises vaporization of the starting material under vacuum and condensation upon a metal wall in which, or on the surface of which, is the activator for enhancement of the photosensitivity of the deposited crystalline material. The activator, preferably oxygen, may be adsorbed by the metal wall or it may comprise part of a coating on the wall. For example, the metal may contain occluded oxygen, or the metal may be oxidized or may be coated with an oxide of another material. vBy control of the amount of oxygen or other activator combined with the metal wall upon which the material is to be deposited and of the temperature difference between the wall and that applied for vaporization of the starting material, the quantity of activating material for combination with the compound may be controlled to yield optimum photosensitivity.
The activated crystalline material deposited upon the metal wall is readily removable by mechanical means and is suitable for use in manufacture of photoelectric cells.
For a better understanding of the invention reference may be had to the accompanying drawing of which the single gure is a diagrammatical representation of apparatus suitable for use in practicing the new process.
The starting material 2, for example, commercial cadmium selenide containing traces of impurities, is placed in a quartz container 4 having a loose fitting lid 6 of tantalum, kmolybdenum or other metal of high melting point containing or carrying an activator for the material to be deposited thereon. A lid of oxidized molybdenum has been found particularly satisfactory in the process. The container 4 with its contents andthe lid 6 is placed 2 within a platinum cylinder 8 about the lower end of which is a coil 10 to which radio frequency current is delivered through leads 12. A cooling coil 14' is positioned about the lid 6 and temperature-responsive means as, for example, a thermocouple indicated diagrammatically at 16 is provided for control of the temperature of the lid. The
entire asesmbly of quartz container 4, platinum cylinder 8, high frequency heating coil10 and cooling coil 14 is enclosed within a chamber 18 adapted to be evacuated as by a connection, diagrammatically indicated at 20, to a vacuum system. The chamber 18 is maintained at a pressure of about l06 mm. and the temperature of the starting material raised by radio frequency induction heating to about 900 C. As the coil surrounds the lower portion only of the platinum cylinder and as the lid 6 is maintained at a lower temperature by means of the cooling coil 14 there will be a temperature differential maintained between the starting material in theV bottom of the yquartz container and the metal-lid 6. Heating is maintained for about thirty minutes after which time the inside surface of the lid 6 will be found covered with a coating of crystals which sticks to the metal lid and may, after cooling, be removed mechanically. With a quartz cylinder of about 1/2" diameter and a height of 1" one run will form suicient deposit from which up to fty small photosensitive cells can be made.
The metal lid 6, instead of being oxidized, may be coated with a thin layer of barium peroxide or with a thin layer containing an activator other than oxygen.
The following gives an indication of the results obtaina'ble by practice of the invention and of the importance of the condition of the metal plate upon which the crystals are deposited. Crystals of commercial grade cadmium selenide were deposited on a molybdenum plate or lid that had ben hydrogen fired to remove all occluded oxygen and to clean the surface and also on a plate of oxidized molybdenum. The deposits on the plates were then removed and the increase in current with equal illumination and equal voltage applied across equally spaced silver paste electrodes on the crystals from each deposit was measured. The dark currents of both deposits were of the same order of magnitude but the currents of illuminated crystals removed from the oxidized molybdenum plate were over one hundred times as large as the currents of illuminated crystals removed from the cleaned plate. When commercial cadmium selenide was deposited on a molybdenum plate coated with barium peroxide, photocurrents over one thousand times greater than those of the deposit on cleaned molybdenum were obtained. The dark currents of the deposit from the barium peroxide coated molybdenum were however substantially larger than the dark currents of the deposits on either the oxidized or cleaned molybdenum plates.v
Photosensitivity of crystals of cadmium selenide deposited on oxidized molybdenum with 22.5 volts across an electrode spacing of about l mm. and illumination of 270 microwatts per square centimeter in the region of maximum spectral response (}\=.750;i) averaged over amperes per watt for four samples.
The above described results obtained when commercial cadmium selenide was deposited under vacuum on oxide coated molybdenum plates are typical of those obtainable by the process of the invention irrespective of the particular starting material and of the particular metal and activator employed. Suitable starting materials have heretofore been indicated. Metals suitable for use as the plate upon which the vaporized starting material deposits are molybdenum, tantalum and platinum.
The following is claimed:
l. The method of enhancing photoconductivity in crystalline material which comprises vaporizing the material under vacuumand depositing the vaporized material on a metal: plate carrying oxygen as an activator, said material being selected from the group consisting of suldes, selenides and tellurides of cadmium, indium, thallium, tin, silver, lead, antimony and bismuth and combinations thereof. v
2'. The method `according to claim 1 wherein the vaporized material is deposited on a metal plate carrying oxygen in the form of an oxide.
3. The method according to claim l wherein the plate is of a metal of the group consisting of molybdenum, tantalum and platinum.
4. The method according to claim 1 wherein the activator is oxygen occluded in the metal plate.
5. The further step in the process of claim 1 which comprises mechanically removing from vthe plate the photoconductive crystals deposited'thereon.
6. The method according to claim 2 wherein the oxide is an oxide of the metal comprising the plate.
7. The method according to claim 2 wherein the oxide is barium peroxide and the plate is of a metal of the group consisting ofmolybednum, tantalum and platinum.
8. The method of enhancing the photoconductivity of cadmium selenide which comprises vaporizing crystals of cadmium selenide under vacuum and depositing the vaporized cadmium selenide on an oxide coated plate of molybdenum.
9. The method of enhancing the photoconductivity of cadmium selenide which comprises vaporizing crystals of cadmium selenide under vacuum and depositing the vaporized cadmium selenide on an oxide coated plate of tantalum.
10. The method of enhancing photoconductivity of cadmium selenide which comprises vaporizing crystals of cadmium selenide under vacuum and depositing the vaporized cadmium selenide on a plate of molybdenum carrying occluded oxygen.
References Cited in the le of this patent UNTTED STATES PATENTS 2,448,517 Cashman Sept. 7, 1948 2,600,579 Ruedy June 17, 1952 2,659,678 Cusano Nov. 17, 1953 2,732,313 Cusano Jan. 24, 1956 2,810,087 Forgue Oct. 15, 1957
Claims (1)
10. THE METHOD OF ENHANCING PHOTOCONDUCTIVITY OF CADMIUM SELENIDE WHICH COMPRISES VAPORIZING CRYSTALS OF CADMIUM SELENIDE UNDER VACUUM AND DEPOSITING THE VAPORIZED CADMIUM SELENIDE ON A PLATE OF MOLYBDENUM CARRYING OCCLUDED OXYGEN.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US541147A US2868736A (en) | 1955-10-18 | 1955-10-18 | Preparation of photosensitive crystals |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US541147A US2868736A (en) | 1955-10-18 | 1955-10-18 | Preparation of photosensitive crystals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| US2868736A true US2868736A (en) | 1959-01-13 |
Family
ID=24158360
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| US541147A Expired - Lifetime US2868736A (en) | 1955-10-18 | 1955-10-18 | Preparation of photosensitive crystals |
Country Status (1)
| Country | Link |
|---|---|
| US (1) | US2868736A (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2997408A (en) * | 1958-05-21 | 1961-08-22 | Itt | Process for producing photoconductive cadmium sulfide |
| US3065112A (en) * | 1958-06-24 | 1962-11-20 | Union Carbide Corp | Process for the production of large semiconductor crystals |
| US3161542A (en) * | 1961-12-29 | 1964-12-15 | Ibm | Peltier heating and cooling of substrates and masks |
| US3188594A (en) * | 1962-01-25 | 1965-06-08 | Gen Electric | Thermally sensitive resistances |
| US3265532A (en) * | 1962-06-06 | 1966-08-09 | American Cyanamid Co | Process of preparing gallium sulfide flakes and photoconductive device using same |
| US3884688A (en) * | 1966-05-16 | 1975-05-20 | Xerox Corp | Photosensitive element employing a vitreous bismuth-selenium film |
| US4101452A (en) * | 1952-09-27 | 1978-07-18 | Electronics Corporation Of America | Lead sulfide activation process |
| US4196257A (en) * | 1978-07-20 | 1980-04-01 | Rca Corporation | Bi-alkali telluride photocathode |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2448517A (en) * | 1944-02-09 | 1948-09-07 | Univ Northwestern | Photocell |
| US2600579A (en) * | 1946-06-05 | 1952-06-17 | Rca Corp | Method of making phosphor screens |
| US2659678A (en) * | 1951-08-23 | 1953-11-17 | Gen Electric | Transparent luminescent screen and method for preparing same |
| US2732313A (en) * | 1956-01-24 | Titanium | ||
| US2810087A (en) * | 1950-11-29 | 1957-10-15 | Rca Corp | Photoconductive orthicon |
-
1955
- 1955-10-18 US US541147A patent/US2868736A/en not_active Expired - Lifetime
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2732313A (en) * | 1956-01-24 | Titanium | ||
| US2448517A (en) * | 1944-02-09 | 1948-09-07 | Univ Northwestern | Photocell |
| US2600579A (en) * | 1946-06-05 | 1952-06-17 | Rca Corp | Method of making phosphor screens |
| US2810087A (en) * | 1950-11-29 | 1957-10-15 | Rca Corp | Photoconductive orthicon |
| US2659678A (en) * | 1951-08-23 | 1953-11-17 | Gen Electric | Transparent luminescent screen and method for preparing same |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4101452A (en) * | 1952-09-27 | 1978-07-18 | Electronics Corporation Of America | Lead sulfide activation process |
| US2997408A (en) * | 1958-05-21 | 1961-08-22 | Itt | Process for producing photoconductive cadmium sulfide |
| US3065112A (en) * | 1958-06-24 | 1962-11-20 | Union Carbide Corp | Process for the production of large semiconductor crystals |
| US3161542A (en) * | 1961-12-29 | 1964-12-15 | Ibm | Peltier heating and cooling of substrates and masks |
| US3188594A (en) * | 1962-01-25 | 1965-06-08 | Gen Electric | Thermally sensitive resistances |
| US3265532A (en) * | 1962-06-06 | 1966-08-09 | American Cyanamid Co | Process of preparing gallium sulfide flakes and photoconductive device using same |
| US3884688A (en) * | 1966-05-16 | 1975-05-20 | Xerox Corp | Photosensitive element employing a vitreous bismuth-selenium film |
| US4196257A (en) * | 1978-07-20 | 1980-04-01 | Rca Corporation | Bi-alkali telluride photocathode |
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