The Short-period (Si_(14)/Ge_1)_(20) and (Si_(28)/Ge)2)_(10) superlattices as Buffer Layers for the Growth of Si_(0.75)Ge_(0.25) Alloy Layers

摘要

2000 A Si_(0.75)Ge_(0.25) alloy layers were grown at 500°C using (Si_(14)/Ge_1)_(20)) and (Si_(28)/Ge_2)_(10) SSL as buffer layers, where buffer layers were grown at different temperatures from 300-450°C. In the first buffers, Ge was deposited as Ge-1-monolayer mode and in the second buffers, it was Ge-2-monolayer mode. Effects of growth temperature of these two buffer layers on the top alloy layers were characterized. From XRD data it was seen that the residual strain decreases with decrease of growth temperature of Ge-1-monolayer mode deposited SSL layers and reached a lower value of about -0.08%. The samples with these buffers also showed a smooth surface with about a constant rms roughness (～12 A) irrespective of growth temperature of the SSL buffer layers. The samples with Ge-2-monolayer mode SSL buffers showed higher residual strain and higher rms roughness than those of the Ge-1-monolayer mode samples. XTEM image of the sample with Ge-1-monolayer mode SSL buffer showed that the top alloy layer is free from dislocations and all the dislocations are in both SSL buffer and substrate. So, we can say that the short-period (Si_(15)/Ge_1)_(20) SL buffer grown at 300°C is better for the growth of relaxed and smooth Si_(0.75)Ge_(0.25) alloy layers.