Nonparabolicity of the conduction band of wurtzite GaN

Using cyclotron resonance, we measure the effective mass, m*, of electrons in AlGaN/GaN heterostructures with densities, n2D∼1 to 6×1012 cm−2. From our extensive data, we extrapolate a band edge mass of (0.208±0.002)me. By comparing our m* data with the results of a multiband k⋅p calculation, we infer that the effect of remote bands is essential in explaining the observed conduction-band nonparabolicity (NP). Our calculation of polaron mass corrections—including finite width and two-dimensional (2D) screening—suggests those to be negligible. It implies that the behavior of m*(n2D) can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values.