A device-oriented study of CdS films deposited by a hot-wall technique

Abstract

A device-oriented study was carried out on thick CdS films (25–30 μm) suitable for solar-cell applications deposited on glass substrates, using a hot-wall technique at a pressure of 1 × 10−6 Torr (1 Torr = 133 Pa). Films were characterized using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The degree of preferred orientation was observed using a simplified version of the Schulz method. Films grown under nominally identical conditions showed two types of growth habit. Type-I films were composed of crystallites having their c axis in a cone with a half angle of 6° about the substrate normal. In Type-11 films, the growth direction was within 11° of the normal to the substrate. Surface grain dimensions varied from 2 to 6 μm, and the room-temperature resistivity varied from 1 to 5 Ω∙cm for the following deposition parameters: substrate temperatures of 230–250 °C, hot-wall temperatures of 370–400 °C, and a deposition rate of 1.2 μm∙min−1. Front-wall CuxS–CdS heterojunctions were made using a hot CuCl dip. Current–voltage characteristics were measured at room temperature. Without optimizing the cell design, open-circuit voltages of 0.45 V and short-circuit currents of 20–30 mA∙cm−2 under AM2 illuminations were observed.