Anisotropy in electronic transport of modulation doped structures having strained InGaAs wells

We have investigated electron mobilities of modulation doped structures grown by molecular beam epitaxy having strained InGaAs wells, and have found that there exists a strong anisotropy in <011 > directions. The anisotropy may be conveniently characterized by the ratio of the mobilities in the two orthogonal directions; this ratio varies with well thickness, becoming significantly greater but less predictable as the well thickness exceeds the critical thickness for dislocation formation. Although most of our data are applicable to growths on the (100) crystal face, we also demonstrated that there is no dependence on slight wafer misorientation. We interpret our results as implying that some small number of dislocations is generated at the onset of InGaAs growth with larger numbers as the critical thickness is passed. Our results have obvious implications for device optimization.