Interfacial properties of (Al,Ga)As/GaAs structures: Effect of substrate temperature during growth by molecular beam epitaxy

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Abstract
Selectively doped (Al,Ga)As/GaAs heterostructures exhibit extremely high electron mobilities, particularly at low temperatures, as a result of electron transfer from doped (Al,Ga)As layer(s) into adjoining GaAs layers. These transferred electrons are confined to within about 100 Å of the interface and the electron mobility is extremely dependent on the structural quality of the heterointerface. By studying low-field mobility of single period (Al,Ga)As/GaAs and inverted GaAs/(Al,Ga)As structures, the quality of each interface can be ascertained. Such single period structures have been prepared by molecular beam epitaxy in a substrate growth temperature range of 600–770 °C to investigate heterointerfaces with GaAs on top of (Al,Ga)As and (Al,Ga)As on top of GaAs. While very good interfaces with (Al,Ga)As on top have been obtained in the growth temperature range of 600–750 °C, the interface quality of the inverted structure has shown a very strong dependence on the substrate temperature. The best interface has been obtained at 700 °C, which is inferior to those with (Al,Ga)As on top. This is attributed to the interface roughness when the binary is grown on top of the ’’rough’’ ternary and perhaps to impurity buildup caused by the Al source. The important impact of this study is that quantum well structures are expected to show the best performance when grown at 700 °C.