Characterization of CuInGeSe_4 thin films and Al-Si/p-CulnGeSe_4/Au heterojunction device

摘要

CuInGeSe~(4)thin films of various thicknesses were prepared on a glass substrate by thermal evaporation followed by selenization at 700 K. Energy dispersive X-ray analysis shows that the CuInGeSe~(4)thin films are near stoichiometric. The X-ray diffraction patterns indicate that the as-deposited CuInGeSe~(4)thin films are amorphous, while the CuInGeSe~(4)thin films annealed at 700 K are polycrystalline with the chalcopyrite phase. The structure of the films was further investigated by transmission electron microscopy and diffraction, with the results verifying the X-ray diffraction data. High-resolution scanning electron microscopy images show well-defined grains that are nearly similar in size. The surface roughness increases with film thickness, as confirmed by atomic force microscopy. The optical transmission and reflection spectra of the CuInGeSe~(4)thin films were recorded over the wavelength range of 400–2500 nm. The variation of the optical parameters of the CuInGeSe~(4)thin films, such as the refractive index n and the optical band gap E ~( g ), as a function of the film thickness was determined. The value of E ~( g )decreases with increasing film thickness. For the studied films, n were estimated from the Swanoepl’s method and were found to increase with increasing film thickness as well as follow the two-term Cauchy dispersion relation. A heterojunction with the configuration Al–Si/p–CuInGeSe~(4)/Au was fabricated. The built-in voltage and the carrier concentration of the heterojunction was determined from the capacitance–voltage measurements at 1 MHz and were found to be 0.61 V and 3.72 × 10_(17)cm_(−3), respectively. Under 1000 W/m_(2)solar simulator illumination, the heterojunction achieved a conversion efficiency of 2.83%.