Dipole scattering in highly polar semiconductor alloys

Abstract

The wide gap polar semiconductors III-V nitrides, II-VI oxides, and ferroelectrics exhibit large spontaneous and piezoelectric polarization due to their nonsymmetric crystal structures. Electrical conductivity in alloys of such crystals is degraded by scattering from the varying polarization coupled to alloy disorder. We have modeled this effect by dipole scattering. We have calculated dipole scattering limited mobility in the relaxation time approximation of the Boltzmann equation. The results are applied to AlxGa1−xN layers coherently strained on GaN. For a typical carrier concentration of 1018(cm−3) in Al0.3Ga0.7N, dipole scattering limited mobilities are 2535 and 3420(cm2∕Vs) at 300 and 77K, respectively. Applying our results to ferroelectric alloys, we reach the interesting conclusion that dipole scattering in such alloys will lead to extremely low mobilities (1–10cm2∕Vs), since it degrades as the square of average dipole moment. This leads us to suggest that digital alloy growth might be necessary to achieve high conductivities in highly polar wide gap alloy semiconductors and ferroelectrics for device applications.