ELECTRICAL CHARACTERIZATION OF VACUUM-DEPOSITED N-CDS P-CDTE HETEROJUNCTION DEVICES/

The effects of post-deposition processes such as CdCl2 dip and/or anne aling in air on the material and device properties of vacuum-evaporate d Au-CdTe/CdS-TO heterojunction solar cells have been investigated. Th e CdCl2 dip followed by air annealing at 300 degrees C for 5 min impro ved the device efficiency significantly, resulting in decreased CdTe r esistivity and enhanced grain size. The temperature-dependent current- voltage analysis indicated that above 280 K interface recombination do minates the current transport mechanism for the as-grown samples, whil e depletion region recombination starts to be dominant after annealing the samples with CdCl2. Below 280 K multistep tunnelling is identifie d to be the dominant transport mechanism. Frequency-dependent capacita nce-voltage studies revealed that after annealing with CdCl2 the densi ty of interface states decreases and the quality of the heterointerfac e improves. The capacitance of the CdS/CdTe heterojunctions has been a nalysed using a model based on the existence of a single dominant trap level, identified at 0.40 eV above the valence band with a concentrat ion of 5.1 x 10(15) Cm-3.