Cranfield University, DCMT – Chemical Bath Deposition Growth of Cadmium Sulphide
Cranfield University, DCMT - Chemical Bath Deposition Growth of Cadmium Sulphide:
"Chemical bath deposition (CBD) is a convenient and low cost technique for growing thin films of many types of materials and is often used to grow the CdS window layer for thin film solar cells. Many different recipes exist for the growth of CdS, and our preferred recipe has evolved over several years. We have recently developed an ultrasonic technique that gives films with a high optical quality. The precursor solution contains cadmium chloride (0.0020 M), ammonium chloride (0.028 M), thiourea (0.057 M) and de-ionized water, with ammonia solution (22%) added to adjust the pH (range of 8.3 to 11.3). Deposition is performed in a double walled water jacket, which is placed in the centre of an ultrasonic bath.
Substrates are mounted on a glass holder and the solution is continuously stirred at a constant speed during deposition, while the bath temperature is increased to a maximum of 70±2 °C from room temperature at a rate of 3 °C min-1. The maximum bath temperature is limited by the rate of homogeneous reaction and the evaporation of ammonia from the chemical bath. This results in a colour change during deposition (see below) and has to be carefully managed to promote deposition on the substrate as opposed to precipitation into the solution. "
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