| 摘要 |
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 Pb1-xSnxTe 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 103V/watt at 77 DEG K and a detectivity peak value which may be as high as up to about 1.5 x 1010cm-Hz1/2/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 14cm-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 DEG and about 350 DEG 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.
|
