Growth rate of hexagonal SiGe multi-quantum wells

Abstract

Direct-band-gap light sources from group IV materials are highly desired for photonic integration. Among the possible candidates is the hex-Si1−xGex system, which has been demonstrated to have a direct band gap at least for x > 65%. Recently, Ge-rich heterostructures of hex-Si1−xGex/Si1−yGey (x < y) have been demonstrated to have a type-I alignment. This unlocks opportunities for devices utilizing low-dimensional structures, such as quantum wells (QWs), based on group IV materials. Multi-quantum-well (MQW) structures can significantly reduce lasing thresholds, and a full understanding of the growth kinetics is necessary to grow MQWs with identical well thicknesses. Here, we report a study of hex-Si1−xGex multishells, of which the growth rate increases by a factor 4 over a shell thickness of 500 nm, indicating nucleation-limited growth. We present a model that hints that the increasing growth rate is due to the accumulation of cubic stacking faults at the growth front. This proposed mechanism is generic for the hex-SiGe system, and it has to be considered for any multilayer structure of hex-SiGe.