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, n(2D)similar to1 to 6x10(12) cm(-2). From our extensive data, we extrapolate a band edge mass of (0.208+/-0.002)m(e). 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(*)(n(2D)) 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. (C) 2003 American Institute of Physics.