Electrical properties of CulnSe2-GaAs junctions

CIS-GaAs heteroj unctions were prepared by evaporation in vacuum CIS films onto the n-type GaAs substrate from a single source. The crystal structure, composition and surface morphology on CIS-GaAs heteroj unctions and CIS films were examined by x- ray diffraction, x-ray fluoresence, electron and optic microscopy methods. The lattice parameters of polycrystal CIS films having a chalcopyrite structure are found to be a=b=5.786Â; c=l 1.572 Â and that of (111) GaAs as a=5.66 Â. It was observed that CIS films were grown on the (1 1 1) GaAs substrate in the direction (112). The current-voltage characteristics, photosensitivity spectra and capacitance-voltage characteristics of CIS-GaAs cells were investigated. The photosensitivity of the cells were found to be in the range A,=0.35-1.0 um and the photovoltaic parameters, namely, the open circuit voltage Voc and the short circuit photocurrent density Jsc were calculated respectively as Voc=467 mV and Jsc=8.9 mA/cm2. The diffusion of copper atoms from CIS film into GaAs substrate was examined by x- ray fluoresence method and the diffusion coefficent of copper was observed to be D= 1.2xl0"8 cm2/s (at 520°C). That it was shown by both the thermal electro-motive force method and as a result of the calculation of the distribution of concentration of holes arising from acceptor-type copper atoms in GaAs, that the p-n homoj unction formed at a depth of around x=8 um. The effects of Na diffusion on the electrical characteristics of CIS films and the photovoltaic parameters of CIS-GaAs cells were investigated. As a result of the diffusion of Na atoms into CIS films, a 100-fold increase in the hole concentration and an improvement in the photovoltaic parameters (VOC=370 mV-470 mV, Jsc=0.8 mA/cm2- 5.5 mA/cm2) were observed. The ideal pCIS-pGaAs-nGaAs hetero-homojunction energy band diagram was drawn and some conclusions were interpreted on this diagram.