EFFECT OF COPPER DIFFUSION ON PHOTOVOLTAIC CHARACTERISTICS OF CUGASE2-GAAS CELLS

CuGaSe2-GaAs heterojunctions were fabricated by fast evaporation of po lycrystalline CuGaSe2 from a single source on n-type GaAs substrates. The best CuGaSe2-GaAs photocell (without an antireflective coating) ex hibited an efficiency of 11.5%, J(sc) = 32mA/cm(2), V-oc = 610 mV and FF = 0.60. The spectral distribution of photosensitivity of CuGaSe2-Ga As junctions extends from 400 to 900 nm. The CuGaSe2 films were charac terized by X-ray diffraction (XRD) and scanning electron microscope (S EM) techniques. XRD analysis indicated that the thin films were strong ly oriented along the (112) plane. SEM studies of CuGaSe2 films showed nearly stoichiometric composition with grain size about 1-2 mu m. The energy dispersive X-ray spectroscopy (EDX) analysis of Cu concentrati on distribution in n-type GaAs showed that Cu diffused from the film i nto n-type GaAs during the growth process resulting in formation of th e latent pn homojunction in substrate. The diffusion coefficient of Cu in GaAs at growth temperature (520 degrees C) estimated from EDX meas urements was 6 x 10(-8) cm(2)/s. (C) 1998 Elsevier Science B.V. All ri ghts reserved.