Preparation and properties of evaporated CdTe films compared with single-crystal CdTe. Progress report no. 6, February 1, 1982-April 30, 1982

Films of n-type CdTe:In have been deposited by hot-wall vacuum evaporation (HWVE) on 7059 glass substrates, BaF/sub 2/ single crystal substrates, metal (Pt, Cr, Mo, Al) coated glass substrates, and single crystal p-type CdTe substrates. Films deposited on 7059 glass show typically a dark resistivity of 2 x 10/sup 5/ ohm-cm and a light resistivity of 3 x 10/sup 2/ ohm-cm. With increasing In source temperature, the resistivity decreases, but actually increases slightly again if the T/sub In/ is raised above 600/sup 0/C. Photoexcitation increases the electron density but does not affect the electron mobility. It appears that the grains are depleted in the dark. Films deposited on BaF/sup 2/ show dark resistivity of about 5 ohm-cm and light resistivity of about 2 ohm-cm, corresponding to electron densities of about 3 x 10/sup 16/ cm/sup -3/ and electron mobilities of about 30 cm/sup 2//V-sec. For doping levels abpove 10/sup 16/ cm/sup -3/ photoexcitation increases the mobility, but not the electron density; it appears that the grains are not depleted in the dark in this case. Cr coated 7059 glass makes an ohmic contact to n-type CdTe films. A Schottky diode formed with a 100A thick Au layer showed V/sub oc/ = 0.46 V, J/sub sc/ = 9 mA/cm/sup 2/ and a solar efficiency of about 2%. An n/p homojunction device was made by HWVE deposition of a 1.5 ..mu..m thick n-type CdTe layer on a p-type CdTe single crystal substrate. Values of V/sub oc/ = 0.73 V and J/sub sc/ = 0.24 mA/cm/sup 2/ were obtained. Grain boundary investigations showed the additive quality of two independent grain boundaries when measured in series, and tested the effects of passivation by Au, Cu, Li and H/sub 2/ in p-type CdTe grain boundaries, and In in n-type CdTe grain boundaries. Marked decreases in grain boundary resistance were observed after Li diffusion and H/sub 2/ diffusion in p-type CdTe