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Anisotropy of effective electron masses in highly doped nonpolar GaN

The anisotropic effective electron masses in wurtzite GaN are determined by generalized infrared spectroscopic ellipsometry. Nonpolar (112¯0) oriented thin films allow accessing both effective masses, m⊥* and m∥*, by determining the screened plasma frequencies. A n-type doping range up to 1.7 × 1020 cm−3 is investigated. The effective mass ratio m⊥*/m∥* is obtained with highest accuracy and is found to be 1.11 independent on electron concentration up to 1.2 × 1020 cm−3. For higher electron concentrations, the conduction band non-parabolicity is mirrored in changes. Absolute values for effective electron masses depend on additional input of carrier concentrations determined by Hall effect measurements. We obtain m⊥*=(0.239±0.004)m0 and m∥*=(0.216±0.003)m0 for the parabolic range of the GaN conduction band. Our data are indication of a parabolic GaN conduction band up to an energy of approximately 400 meV above the conduction band minimum.