Electrical resistors – Resistance value responsive to a condition – Photoconductive
Patent
1976-05-27
1978-04-25
Albritton, C. L.
Electrical resistors
Resistance value responsive to a condition
Photoconductive
204192P, 357 30, H01L 3108
Patent
active
040865550
ABSTRACT:
An improved photoconductive sensor is provided which includes a substrate of calcium fluoride or barium fluoride in monocrystalline form upon which has been sputtered under controlled conditions a thin unannealed monocrystalline film having the formula Pb.sub.1-x Sn.sub.x Te where x = about 0-0.3. The conditions under which the film is deposited are controlled so that the film exhibits a cutoff wavelength between about 6.mu.m and about 15.mu.m, a photoconductive responsivity which may be as high as up to about 10.sup.3 V/watt at 77.degree. K and a detectivity peak value which may be as high as up to about 1.5 .times. 10.sup.10 cm-Hz.sup.1/2 /watt at frequencies above the 1/f noise frequency. The film also exhibits a fast response time of less than about 100 nanoseconds and is usually present in a thickness, for example about 1-2.mu.m, corresponding to high quantum efficiency and minimal contribution of unexcited film to detector noise. Moreover, the film has a low carrier concentration, a predetermined carrier type, and a high Hall mobility and is stable over long periods of time. The carrier concentration is as low as about 10.sup. 14 cm.sup.-3, the film thickness is usually about 1-2 .mu.m and the film composition is about stoichiometric. In order to provide the sensor with these characteristics, the film is deposited at a selected temperature between about 220.degree. and about 350.degree. C. in argon, preferably also in the presence of a small amount of dopant gas selected from nitrogen and oxygen and utilizing a film growth rate of between about 0.1 and 3.0.mu.m/hr and alternatively also utilizing a voltage bias to the substrate between about +30 volts and about -30 volts and adjacent the critical switching voltage at which the carrier type changes from p to n or n to p. Accordingly, minimal carrier concentration and high mobility as well as desired carrier type are provided. The finished sensor has a noise level approaching Johnson noise and can be easily incorporated into improved infrared photoconductive devices.
REFERENCES:
patent: 3961998 (1976-06-01), Scharnhorst et al.
C. Corsi, Pb.sub.1-x Sn.sub.x Te Layers by R.F. Multicathode Sputtering, Journal of Applied Physics, vol. 45, No. 8, Aug. 1974, pp. 3467-3471.
C. Corsi et al., Pb.sub.x Sn.sub.1-x Te Epitaxial Layers by R.F. Multicathode Sputtering, (p) C.N.R. Laboratorio Elettronica Stato Solido-GNS.M. Rome, Italy (9/73).
C. Corsi et al., Infrared Detector Arrays by R.F. Sputtering, Infrared Physics, 1972, vol. 12, pp. 271-275, Pergamon Press in Great Britain.
I. Melngailis et al., Photovoltaic Effect in Pb.sub.x Sn.sub.1-x Te Diodes, Applied Physics Letters, vol. 9, No. 8, 10/15/66, pp. 304-305.
K. W. Nill et al., Laser Emission from Metal-Semiconductor Barriers on PbTe and Pb.sub..8 Sn.sub..2 Te, Applied Physics Letters, vol. 16, No. 10, 5/15/70, pp. 375-377.
Crisp Michael J.
Krikorian Esther
Albritton C. L.
Bissell Henry M.
General Dynamics Corporation
Johnson Edward B.
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