Photoconductivity of CdS–CdSe granular films: influence of microstructure

Abstract

We study experimentally the photoresistance of CdS-CdSe sintered granular films obtained by the screen printing method. We mostly focus on the dependences of photoresistance on film's microstructure, which varies with changing heat-treatment conditions. The minimum photoresistance is found for samples with compact packing of individual grains, which nevertheless are separated by gaps. Such a microstructure is typical for films heat-treated during an optimal time of 30 min at the temperature of 823 K. In order to understand whether the dominant mechanism of charge transfer is identical with the one in monocrystals, we perform temperature measurements of photoresistance. Corresponding curves have the same nonmonotonic shape as in CdSe monocrystals.Namely, photoresistance first increases with the growth of temperature, and then starts to decrease.Thus we conclude that the basic mechanism is also the same, as in monocrystals, and it is based on two types of centers in the forbidden gap. We suggest that the optimal heat-treatment time depends on two competing mechanisms: improvement of film's connectivity and its oxidation. Photoresistance is also measured in vacuum and in helium atmosphere, which suppress oxygen and water absorption/chemisorption at intergrain boundaries. We demonstrate that this suppression decreases photoresistance, especially at high temperatures.

Physicochemical features of dielectrical nano-barrier layers in CdSe_xS_1-x films formed by screen printing method

“…The second method included the direct synthesis of CdSe x S 1-x films on substrate from the paste consisting of original powders. In detail the process of screen printed film formation is described in [4][5][6]. The photosensitivity thermal activation was carried out in a diffusion furnace SDO 125/4 at the temperature of 525-600 °С during 5-60 min in nitrogen and air atmosphere as well as in the regime of quasi-closed air atmosphere.…”

Tunable p- and n-type Nb:TiO2 and performance optimizing of self-powered Nb:TiO2/CdS photodetectors

“…As a wide bandgap semiconductor, titanium dioxide (TiO 2 ) has attracted great attention for its particular advantages of rich abundance, low-cost, temperature stability and chemical stability [24]. Cadmium sulfide (CdS) is widely used as an n-type photosensitive semiconductor material in optoelectronic devices [25][26][27][28][29][30]. In a TiO 2 /CdS heterojunction structure, TiO 2 can promote the separation of photon-generated electron-hole pairs from CdS [31,32].…”