Kinetic roughening in low-temperature MBE growth of III-As heterostructures on InP(111)B

(In,Ga)As/(In,Al)As superlattices (SLs) grown on InP(111)B are among the most challenging systems to realize by molecular beam epitaxy (MBE), particularly under low-temperature (LT) conditions. To investigate the impact of the low substrate temperature Ts, 50 periods of (In,Ga)As/(In,Al)As were grown on 2° misoriented InP(111)B substrates. Ts was decreased stepwise every 10 SL periods, from 450 to 250 °C, while all other growth parameters were kept constant. The microstructure was investigated using (scanning) transmission electron microscopy. While growth at Ts = 450 °C results in regular and well-defined SL periods, a dramatic degradation of the microstructure is observed as Ts decreases. The first significant change appears upon lowering Ts from 450 to 400 °C, and the resulting periods display a high density of in-plane microtwins and stacking faults. A further reduction in Ts promotes the formation of increasingly defective layers, which in turn give rise to hillocks, cone-like defects, pores, and localized amorphous regions. As discussed here, the observed microstructure is consistent with the breakdown of epitaxy associated with LT-MBE. We show that the distinctive morphology of (In,Ga)As/(In,Al)As SLs and its dependence on Ts can be explained in terms of the critical role of the step-flow growth mode and the influence of Ehrlich–Schwoebel barriers at the step edges. Specifically, the observed microstructure arises from kinetic roughening caused by the progressive inability to sustain step-flow growth as Ts decreases. Given the critical role of surface kinetics, we propose several strategies to improve the overall structural quality.