Roughness-induced piezoelectric scattering in lattice-mismatched semiconductor quantum wells

We present a theory of the mobility of electrons in real semiconductor quantum wells (QW’s) made from lattice-mismatched epitaxial layers. In the case of zinc-blende structure QW’s, we prove that besides the conventional scattering mechanisms, e.g., impurity doping, surface roughness, and alloy disorder there exists an ad hoc scattering source, which is due to a large fluctuating density of roughness-induced piezoelectric charges. Scattering by their piezoelectric field is found to be a new important scattering mechanism limiting the electron mobility of real strained QW’s, especially those with a well thickness of the order of or greater than 50 Å. By incorporating this scattering into the theory, we are able to provide a perfect explanation for the low-temperature electron mobility measured in lattice-mismatched InGaAs-based QW’s, which has not been understood starting from the so far-known scattering sources. The possibility of applying our theory to other lattice-mismatched systems such as Si/SiGe heterostructures and nitride-based QW’s is outlined.