The Development of Infrared Photosensitive Material Based on Polycrystalline PbS Films

Abstract

Polycrystalline thin films of lead sulphide were deposited on glass substrates by the hot wall technique. The grain size varied from 100 to 500 A by varying the growth rate and the substrate temperature. The grain boundaries are assumed to influence the optoelectronic properties of polycrystalline films by generating potential energy relieves, estimated to reach 0.1 eV. We investigated the influence of the barrier height by introducing impurity atmospheres into the grain boundaries. Oxygen and indium were introduced into the films by diffusion from a gas phase. Conductivity was measured in the 80-300 K range. It rises with increasing temperature in oxygen doped films, indicating that conductivity is a thermal activation process. In the same time the conductivity of In doped PbS films decreases with temperature like in PbS single crystals. Photoconductivity was observed in films annealed in oxygen, which was significant up to room temperature. Carrier lifetime was found to decrease with rising temperature and be larger in films annealed in oxygen.A model is proposed to explain the optoelectronic behavior of the polycrystalline films. It is proposed that charge accumulation near grain boundaries set up potential barriers for free carriers. The barriers increase by oxygen and decreases by indium doping. The charge carriers generated by an illumination become spatially separated at grain boundaries. This separation retards their recombination and increases their lifetime, giving rise to persistent photoconductivity and potential high photosensitivity.

Effect of GaAs Substrate Micropatterning on Threading Dislocation Density in Solution-Deposited Lead Sulfide Thin Films

“…Lead sulfide (PbS) thin films are technologically significant due to their importance as infrared radiation detectors and emitters. − GaAs is a direct band gap semiconductor ( E g = 1.42 eV, at 300 K) with excellent optical properties that have been widely exploited in LEDs, lasers, and optical detectors. Deposition of thin PbS films on GaAs opens the path for integration of PbS IR optoelectronics with GaAs-based technology and photothermal conversion applications. , Commonly used techniques for PbS films growth include reactive evaporation, spray pyrolysis, hot wall techniques, and vapor phase epitaxy, − however all these techniques are complicated and costly, while chemical solution deposition (CD) is a straightforward and low-cost technique for PbS film growth. Chemical epitaxy of PbS on GaAs has been shown to result in twin-like orientation relationship later shown to depend upon the crystallographic orientation of the substrate microfacet .…”

The Influence of Oxygen on the Electrical Properties of Bulk and Thin Films of PbTe Semiconductors

“…Recently, interest in the lead chalcogenides has been stimulated by theoretical predictions [1] and subsequent experimental observations [2] of the enhancement in the thermoelectric figure of merit ZT in superlattices based on IV-VI semiconductor compounds. The surface absorption of oxygen, acting as an acceptor, significantly affects the properties of lead chalcogenides and, therefore, of the devices based on these compounds [3][4][5][6]. High temperature annealing (T an = 500-600 o C) in an oxygen-containing atmosphere led to high photosensitivity of vacuum-evaporated polycrystalline PbS films ("physical" films) that appeared in parallel to the formation of various oxygen containing surface phases e.g., PbO, PbO 2 , PbSO 3 [3,4].…”