EFFECT OF GA INCORPORATION IN POLYCRYSTALLINE CUINSE2 FILMS

CuIn1-xGaxSe2 (0 less than or equal to x less than or equal to 0.25) f ilms were deposited (on glass substrates at similar to 770 K) by four source coevaporation technique. The thickness and average grain size o f the films varied within 3-3.5 mu m and 0.2-0.5 mu m, respectively, w ith small variation of surface roughness (18-24 nm). The films were ch aracterized by measuring the microstructural, optical and mechanical p roperties. A new optical technique was used to estimate the strain/str ess in the polycrystalline films from the broadening of the optical ab sorption band tail. Addition of Ga increased the stress from 1.37 x 10 (8) to 2.78 x 10(8) dynes/cm(2) while the density of trap states (Q(t) ) at the grain boundaries varied from 7.2 x 10(9) to 1.3 x 10(11) cm(- 2). The corresponding variation in the average built electric field (F -av) at the grain-surfaces of the polycrystalline films was estimated to be 0.15-2.95 x 10(4) V/cm. Surface photovoltage (SPV) measurements of CuIn1-xGaxSe2/CdS devices indicated minority carrier diffusion leng ths (L(n)) to be similar to 1 mu m and 0.7 mu m, respectively, for x = 0 and x = 0.25. Copyright (C) 1996 Elsevier Science Ltd