Synthesis of Ultrapure Superstructural Compounds CdS-PbS as a Phenomenon of Absolute Ordering of Phases of Solid Solution of CdxPb1−xS: Development of IR Photodetectors for Space
摘要
During the development of high-speed photoresistors (PR) based on thin films, a stabilization of the composition near x = 0.06 was detected in the region of the existence of a solid CdxPb1-xS solution (x ≤ 0.24). The band gap is Eg (295 K) = 0.524 eV, and the Hall mobility of the p-type is µH = 10 − 15 cm2/ (V·s) at a thin films thickness of h = 1.5 μm. When cooled to 160 K, the conductivity of the films decreases by 30 000 times. This indicates a transition to dielectric behavior. For Cd0.06Pb0.94S film, the temperature coefficient dE/dT (160–323 K) = + 1.25 · 10− 4 eV·K-1, which is 4 times less than dE/dT for PbS. During the film growth process, the red photoconductivity boundary at 10% of the maximum undergoes sharp shifts, from 1.55 μm to 2.36 μm. The combination of these anomalous parameters for the CdxPb1-xS film (x = 0.18–0.06, x decreases during growth) is interpreted as the formation of a sandwich of ultrapure super structured semiconductor chemical compounds such as Cd3Pb13S16, Cd5Pb27S32, Cd1Pb7S8 and Cd1Pb15S16 in each microcrystal of this thin film. These stoichiometric compounds are structurally completely ordered phases of a solid substitution solution. This represents the first observation of this kind of ultra-purification effect of a photoconductive film achieved in one stage of crystallization. Cd1Pb15S16 PR for the 0.25–2.4 μm range have a time constant τ = 8 − 35 µs and D*(1000; 1; 1.8) = (6 − 15) · 1010 cm · W⁻¹ · Hz1/2. PR are characterized by a low level of 1/f noise and can also operate in relay-like mode (10 MOhm / 100 kOhm) at irradiation up to 100 mW/cm2 up to T = + 80 ℃. The matrices on these PR can be used as opto-isolators to control op-amp matrices with a speed increase of 10 thousand times compared to CdS-CdSe PR.