Formation Of ZnTe: Cu/Ti Contacts at High Temperature for CdS/CdTe Devices

We study the performance of CdS/CdTe thin-film devices contacted with ZnTe:Cu/Ti of various thickness at a higher-than-optimum temperature of ~360degC. At this temperature, optimum device performance requires the same thickness of ZnTe:Cu as for similar contacts formed at a lower temperature of 320degC. C-V analysis indicates that a ZnTe:Cu layer thickness of <~0.5 mum does not yield the degree of CdTe net acceptor concentration necessary to reduce space charge width to its optimum value for n-p device operation. The thickest ZnTe:Cu layer investigated (1mum) yields the highest CdTe net acceptor concentration, lowest value of J_o, and highest V_oc. However, performance is limited for this device by poor fill factor. We suggest poor fill factor is due to Cu-related acceptors compensating donors in CdS