Effects of intrinsic and extrinsic point defects on epitaxial single crystal copper-indium(1-x)-gallium(x)-diselenide

From the results presented here a number of conclusions regarding the effects of point defects on the properties of epitaxial single crystal CuIn{dollar}rmsb{lcub}1-x{rcub}Gasb{lcub}x{rcub}Sesb2{dollar} (CIGS) may be drawn. These conclusions may be divided into three categories: the effects of point defects on Ga diffusion and diffusivity, the influence of impurities and alloying elements on doping and mobility, and the effects of impurities on minority carrier recombination kinetics.; The diffusivity of Ga into CIGS during growth was found to be strongly dependent of the Cu/In ratio of the growing layer. Diffusivity ranged from a minimum of {dollar}rm2.7times10sp{lcub}-13{rcub} cmsp2{dollar}/s at Cu/In = 0.94 to {dollar}5 times 10sp{lcub}-11{rcub}{dollar} cm{dollar}sp2{dollar}/s at Cu/In = 1.41 and {dollar}7times10sp{lcub}-12{rcub}{dollar} cm{dollar}sp2{dollar}/s at Cu/In = 0.43. The diffusion occurred by a vacancy mechanism with Ga, apparently, diffusing through either Cu or In vacancies. The sharp change in diffusivity with changing Cu/In ratio helps to explain the difficulty in maintaining a desired Ga profile in polycrystalline CIGS device absorber layers.; Increasing Ga content was found to increase both acceptor and donor density. The decrease in J{dollar}sb{lcub}rm sc{rcub}{dollar} found in Ga-containing polycrystalline devices, is likely caused by a large increase in acceptor density, which may cause less inversion of the surface of the p-type CIGS making the junction more sensitive to surface states.; The effect of adding Na by diffusion from either NaOH or Na{dollar}sp2{dollar}Se was to reduce the donor density. These results help to explain results in polycrystalline CIGS devices where Na increased hole concentrations, V{dollar}sb{lcub}rm oc{rcub},{dollar} and device efficiency.; Unlike Ga and Na, Cr and Se were not found to have any strong effect when added in concentrations {dollar}le{dollar}10{dollar}sp{lcub}19{rcub}{dollar} cm{dollar}sp{lcub}-3{rcub}{dollar} using ion implantation. The lack of an effect of Se on doping conclusively determines that Na has an effect beyond simply introducing either O or Se into the bulk of the CIGS. While both implanted Se and Cr created large numbers of donors and acceptors before being annealed, both caused a decrease in acceptor concentration after annealing with the effect of Cr being larger than that of Se. Both Se and Cr reduced hole mobility over the entire temperature range investigated. These results imply that CIGS-based devices should be insensitive to accidental transition metal contamination.; The steady state photoconductivity of samples which had been ion implanted with Se and Cr, as well as samples which were contaminated with Na by diffusion, was measured. These measurements were made to determine whether contamination by these elements or severe radiation damage affects minority carrier recombination kinetics. In all cases the photoconductivity was found to be unaffected other than by changes in mobility. (Abstract shortened by UMI.)...