Anisotropy of effective electron masses in highly doped nonpolar GaN

摘要

The anisotropic effective electron masses in wurtzite GaN are determined by generalized infrared spectroscopic ellipsometry. Nonpolar (1120) 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 × 10~(20)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 × 10~(20)cm~(-3). For higher electro 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)m_0 and m~*_‖ = (0.216 ± 0.003)m_0 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.