Electron effective mass in Al_0.72Ga_0.28N alloys determined by mid-infrared optical Hall effect

The effective electron mass parameter in Si-doped Al_0.72Ga _0.28N is determined to be m = (0.336 ± 0.020) m 0 from mid-infrared optical Hall effect measurements. No significant anisotropy of the effective electron mass parameter is found supporting theoretical predictions. Assuming a linear change of the effective electron mass with the Al content in AlGaN alloys and m = 0.232 m 0 for GaN, an average effective electron mass of m = 0.376 m 0 can be extrapolated for AlN. The analysis of mid-infrared spectroscopic ellipsometry measurements further confirms the two phonon mode behavior of the E₁(TO) and one phonon mode behavior of the A ₁(LO) phonon mode in high-Al-content AlGaN alloys as seen in previous Raman scattering studies.