EFFECTS OF SURFACE PREPARATION ON THE PROPERTIES OF SINGLE CRYSTAL CADMIUM-TELLURIUM JUNCTIONS

The effects of surface preparation on the properties of single crystal CdTe junctions have been investigated through characterization of metal/CdTe junctions and heterojunctions. Oriented surfaces include air-cleaved (110) surfaces, etched (110) and (111) surfaces, and etched surfaces subjected to a hydrogen heat treatment.; Metal/CdTe junctions formed on cleaved surfaces exhibit diode characteristics that obey the thermionic emission model modified by the effects of a thin interfacial oxide layer. The measured barrier height depends on metal work function and reached 0.99 V in an Al/CdTe junction.; Etched surfaces result in metal/CdTe junctions with a barrier height of 0.7 V. No dependence of the barrier height on the metal work function is observed, suggesting the presence of an etch-induced layer on the etched surface partially governing its properties. Heat treatment of a polished and etched surface results in metal/CdTe junctions with characteristics similar to those of junctions formed on cleaved surfaces. Dependence of barrier height on metal work function is observed, suggesting the removal of an etch-induced suface layer by the heat treatment.; Auger analysis indicated the presence of excess Te and detectable concentrations of Br on the etched surfaces, whereas no excess Te or Br was detected on the heat treated surface.; ITO/CdTe heterojunctions were prepared on three different surfaces. An air heat treatment necessary for ITO transparency results in serious degradation of the diode characteristics for junctions formed on both cleaved and heat treated surfaces. Junctions on etched surfaces are relatively unaltered, supporting the presence of an etch-induced layer on the etched surface governing its properties. Resulting solar efficiencies as high as 10.5% were observed for ITO/CdTe heterojunctions formed on etched surfaces. These heterojunctions, which have been stable for over 9 months, have photovoltaic properties ultimately governed by the interface region.