Alloy disorder scattering contribution to low-temperature electron mobility in semiconductor quantum well structures

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Abstract
We present calculations of the alloy disorder effect on the low-temperature mobility of quasi-two-dimensionally-confined electrons in thin square quantum wells involving a ternary III-V semiconductor alloy as either the barrier layer (e.g., GaAs/AlxGa1−xAs) or the well layer itself (e.g., InxGa1−xAs/InP). It is shown that in the former case the alloy disorder at and near the interface arising due to chemical intermixing gives a significant contribution to the electron scattering. Even for structurally and chemically ideal interfaces, the alloy disorder scattering from the barrier layer is found to be comparable to that calculated previously on the basis of fluctuations in the width of the potential well. For well layers made of a ternary alloy, the alloy disorder scattering in the well is shown to yield a dominant contribution to electron scattering. Results are presented for the low-temperature mobility as a function of areal electron density and well thickness for the lattice matched systems In0.53Ga0.47As/InP and GaAs/AlxGa1−xAs. Specifically, it is estimated that for the In0.53Ga0.47As/InP system, the mobility is limited by the alloy disorder scattering once the ionized donors in the barrier layer are separated by an undoped spacer layer of thickness exceeding about 100 Å. It is also shown that the alloy disorder limited mobility in a quantum well made of an alloy can exceed that in the corresponding bulk alloy. Results are also included for the alloy composition dependence of the mobility. Wherever possible, these results are compared with the available relevant experimental mobility values and the implications discussed.