Atomic force microscopy study of ZnSeGaAs heteroepitaxy processes by metalorganic vapour phase epitaxy

We investigate the initial growth of ZnSe on (001) GaAs in metalorganic vapour phase epitaxy using atomic force microscopy, X-ray diffraction, and photoluminescence. GaAs surfaces become atomically flat after thermal cleaning at a temperature of 620–750°C. The property of ZnSe films is critically dependent on the GaAs surface preparation and the flow rate ratio of Se to Zn. The simultaneous As flow during thermal cleaning is effective to grow high-quality ZnSe films. The growth processes at the initial stages of heteroepitaxy of ZnSe on GaAs are dominated by the two-dimensional growth mode for Zn-rich growth conditions, while those are dominated by the three-dimensional growth mode as the Se flow rate increased. The optimum condition for the ZnSe optical quality is different from that for the initial two-dimensional growth. We demonstrate that the 2-step growth is effective to grow atomically flat ZnSe films with better optical quality.