There is considerable interest in the deposition of compound semiconductors by methods which involve relatively low capital expense and are technically undemanding on the experimentalist. One process to meet these criteria is Chemical Bath Deposition (CBD). Such processing methods are particularly appropriate for the production of devices for which large areas and low cost are essential, such as the BP Solar Ltd “Apollo” cells based on CdS:CdTe heterojunctions.
The electrical and optical properties of these devices have been investigated with respect to impurity profiles of 16-O, 34-S, 35-Cl and 12-C in the CdTe and CdS:CdTe interface. Device characteristics (e.g. Voc and Rs) have been correlated with SIMS data. The distribution of the carbon contaminant appears to influence the chloride-promoted recrystallisation of CdTe. XPS analysis of CdS layers appears to indicate that the annealing process induces the formation of a chloride-rich surface layer, which may promote the n- to p- type thermal conversion of CdTe.