Published: 1980
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Thin-film InP/CdS structures were prepared by depositing, in sequence, ITO on a low-cost glass substrate, CdS on the ITO by thermal evaporation, and InP on the CdS by planar reactive deposition (PRD). Films of CdS, 15 .mu.m thick, were recrystallized in flowing H2/H2S at 500°C. Lateral dimensions of typical grains were 50.mu.m with values up to 200 .mu.m. The sheet resistance of the recrystallized CdS (RXCdS) was lowered from greater than 105 .cap omega./O = cm2 to values as low as 16 .cap omega./O = cm2 by annealing in either H2 Cd atmospheres. Epitaxy of InP was undertaken on (100) InP at a substrate temperature of 320°C. Room-temperature electron mobilities of about 2000 cm2/V-sec were found. Mobilities and hole concentrations of 60 cm2/V-sec and 1017 cm-3, respectively, were achieved with Be-doped films. P-type films with hole concentrations as high as a few times 1018cm-3 were achieved with increased doping. Be-doped InP was deposited onto the RXCdS/ITO/GLASS substrate to form a thin-film cell. However, p-type InP could not be prepared with CdS as a substrat4e, presumably due to interdiffusion or vapor transport of sulfur. Consequently, blocking action and a photovoltage could only be achieved using a gold Schottky barrier on the InP/RXCdS/ITO/GLASS structure. Plans for the next quarter include determining whether n-type doping from the CdS occurs by either interdiffusion or vapor transport, characterizing InP epitaxy on the RXCdS, and preparing additional thin-film structures.