Electrical Conductivity Measurements in Evaporated Cadmium Telluride Thin Films.
Abstract
Available from UMI in association with The British Library. An investigation has been made into the electrical, optical and structural properties of CdTe thin films. Capacitance measurements indicate that the films have a relative permittivity of 9.6 (Merck Patinal) and 10.68 (Balzers). The dark resistivity was found to be of the order of 10^4 Omega-m, with its precise value depending on the deposition conditions. From dc J-V measurements, at low fields hopping conduction has been observed particularly at low temperature, while at high fields space-charge-limited current and, for doped material, the Poole-Frenkel effect have been observed. In the space-charge limited region both a discrete level and an exponential trap distribution have been identified in evaporated CdTe thin films. The ac conductivity of these samples is proportional to omega^{rm s}, where omega is the angular frequency and s is a temperature-dependent quantity; the value of s decreases with increase in temperature. An analysis of the low temperature results indicates that the mechanism of conduction is via hopping. The ac capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature and can be satisfactorily explained in terms of the model of Goswami and Goswami. Optical absorption studies have also been performed on CdTe thin films, and it has been shown that the optical band gap increases with the thickness of the films. X-ray diffraction studies showed that the films are microcrystalline with typical grain size 74 nm and with preferred orientation in the (111) direction. The micro-strain and the grain size of CdTe thin films depend on deposition parameters such as rate of evaporation, thickness and the substrate temperature.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1990
- Bibcode:
- 1990PhDT.......250B
- Keywords:
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- Engineering: Materials Science; Physics: Condensed Matter