Full-band polar optical phonon scattering analysis and negative differential conductivity in wurtzite GaN

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Abstract
GaN has promising features for high-field electronics applications. To scrutinize these transport-related properties, primarily the dominant scattering mechanism in this material needs to be well characterized. In the quest for Bloch oscillations in bulk GaN, our aim is to conduct a full-band scattering analysis requiring very high energies where parabolic approximation is far from applicable. For this purpose, we first obtain an accurate band structure for the conduction band of wurtzite GaN based on the empirical pseudopotential method, using the most recent experimental data as the input. We compute the scattering rate, relevant up to room temperatures, due to longitudinal-optical-like and transverse-optical-like polar phonon modes along several (high-symmetry) directions, from the conduction band minimum at the zone center to the half of the reciprocal lattice vector in each direction. We observe that the location and the symmetry of the neighboring valleys to the route play a decisive role on the scattering rates. The observation of Bloch oscillations in bulk wurtzite GaN is doomed by the very large value of the polar scattering rate. However, there exists the possibility of a negative differential conductivity driven by the negative effective mass part of the band structure for fields above 2.3 MV/cm for wurtzite GaN.

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