GROWTH, STRUCTURE AND COMPOSITION OF ELECTRODEPOSITED CDTE THIN-FILMS FOR SOLAR-CELLS

An organic electrolytic deposition process for preparation of stoichiometric CdTe film for solar cell applications is described. Increase in deposition current modifies crystalline growth phase from hexagonal to cubic and surface microstructure from lateral crystallites to nodular grains. Initial surface morphology affects the etched and annealed microstructure of CdTe. Monocrystalline CdTe film growth occurs at low deposition currents < 0.25 mA/cm(2) due to low nucleation rate and surface diffusion of adions on the substrate to growth sites. Morphological and structural changes are caused by differential activity of adions at different facets of crystallites in CdTe during growth. Lesser defect density in CdTe enables insitu doping and p - conversion by phosphorous atoms. An upper limit of 20 at% of dopant in a deposition bath is set by nonstoichiometry of CdTe film due to concurrent high deposition of phosphorous resulting in depletion of Cd. P dopants occupy Te sites at concentration < 1 X 10(-5) Molar as inferred by the disappearing of the Auger Te(NOO) line and analysis of the Te(MNN) line shape. Substitutional location of P during growth results in CdTe films of p-type with resistivities 20-30 ohm . cm in the as-deposited state, without O-2 annealing. Further reduction in resistivity is prevented by formation of P-CD and PiPCD compensating defects in CdTe.