Crystal growth and physical properties of chalcopyrite and related materials

Research on crystal growth and physical properties of chalcopyrite and related compounds is reviewed and recent developments are reported. High quality epitaxial thin films were grown by molecular beam epitaxy (MBE) and halogen transport techniques in order to clarify the intrinsic physical properties and the effect of impurities and defects on optical and transport properties. We find that high quality CuInSe₂ and CuGaSe₂ thin films arc prepared onto quasi-lattice matched InGaAs substrates by MBE, the quality of which is demonstrated by the photoluminescence spectrum dominated by a band-edge emission. The crystal structure and strain-related phenomenon such as relaxation, lattice distortion due to defects, anisotropic morphology and strain-enhanced interdiffusion were investigated by high-resolution X-ray diffraction, TEM and AFM techniques. The results have established the key parameters to grow high-quality thin films, e.g., the optimum (Cu/In) ratio. As a result, carrier control by impurity doping during MBE growth has become feasible. In this report, the research body (Novel Photovoltaic Materials Laboratory) is briefly introduced and the recent research topics are described.