Material properties and growth mechanism of CuInSe2 prepared by H2Se treatment of metallic alloys

A fundamental understanding of the mechanism of growth of CuInSe2 is essent ial for the production of device quality material. In this contribution, th e growth kinetics of thin film CuInSe2 are investigated in the special case of H2Se/Ar treated copper-indium metallic alloys. A systematic study was c onducted in which the evolution of surface morphologies by scanning electro n microscopy (SEM), formation of crystalline X-ray diffraction (XRD) and va riation in film composition, energy dispersive spectrometry (EDS) were eval uated during various stages of selenization. SEM and XRD studies revealed a dramatic improvement in crystalline quality with increasing selenization t emperature. SEM studies indicated a substantial increase in grain size (0.2 mu m --> 1 mu m) when the reaction temperature was increased from 150 degr ees C to 450 degrees C. XRD studies revealed the presence of mostly binary phases (i.e. Cu11In9, InSe, In6Se7 and CuSe) at selenization temperatures u p to 250 degrees C. CuInSe2 was found to be the dominant phase at 350 degre es C and the film was almost completely converted to single phase material at 450 degrees C. The composition of the selenized films remained virtually unchanged in the temperature range between 150 degrees C and 350 degrees C . However, reaction of the metallic alloys to H2Se/Ar at temperatures aroun d 450 degrees C resulted in a significant loss of indium from the films and subsequently to an increase in the Cu/In atomic ratio. The variation in cr ystalline quality of the films during various stages of selenization was al so clearly reflected by low temperature photoluminescence (PL) studies. Vir tually no PL response was detected from samples selenized at low temperatur es below 350 degrees C, compared to rather strong emissions from samples se lenized at higher temperatures around 450 degrees C. Furthermore, a signifi cant difference in PL response was detected from samples selenized at 350 d egrees C and 450 degrees C, respectively. Comparative studies indicated the presence of a free-to-bound transition (at 0.992 eV) only in the case of s amples selenized at 450 degrees C, which indicated that these specific poin t defects (V-ln) are created at high selenization temperatures. This observ ation is consistent with EDS results, indicating a substantial loss of In f rom samples selenized in this high temperature range. PL spectra from sampl es selenized at 350 degrees C were also characterized by a broad peak close to the band gap value, which was attributed to the presence of point defec ts associated with In-rich secondary phases. The improvement in crystalline quality with increased selenization temperatures and reaction periods was also clearly reflected by the reduction in the FWHM values of the PL peaks. The information gained from this study played an important role in the pro duction of high quality films in our laboratories.