Research of surface morphology in Ga(In)As epilayers on Ge grown by MOVPE for multi-junction solar cells

Abstract

The surface morphology of Ga(In)As films grown on offcut Ge substrates was characterized with atomic force microscopy (AFM) and scanning electron microscopy (SEM). We have investigated the effect of growth parameters on the Ga(In)As films by metal-organic vapor-phase epitaxy (MOVPE). The interface properties strongly depended on the growth conditions. We found that two-step growth temperatures can obtain good morphology and suppress the antiphase domains (APDs). Under optimized growth conditions APD-free Ga(In)As film on Ge was obtained. Our results indicate that the 6° offcut Ge substrate with two-step temperatures growth 770 and 650 °C, are the optimum set of growth conditions for the buffer layer growth of Ga(In)As/Ge heterostructure solar cells. The root mean square (rms) roughness was approximately 4.58 nm over a 10×10 μm 2 area. The buffer Ga(In)As films on Ge substrate were developed in preparation for growing multi-junction solar cells and obtained high performance with good morphology.