Electron effective mass in unintentionally doped In${}_{0.33}$Ga${}_{0.67}$N determined by mid-infrared optical Hall effect

Abstract

Mid-infrared optical Hall effect measurements are used to determine the free charge carrier parameters of an unintentionally doped wurtzite-structure $c$-plane oriented In${}_{0.33}$Ga${}_{0.67}$N epitaxial layer. Room temperature electron effective mass parameters of $m_{\perp }^{\ast }=(0.205\pm 0.013)m_0$ and $m_{\parallel }^{\ast }=(0.204\pm 0.016)m_0$ for polarization perpendicular and parallel to the $c$-axis, respectively, were determined. The free electron concentration was obtained as $(1.7\pm 0.2)\times 10^{19}$cm${}^{-3}$. Within our uncertainty limits we detect no anisotropy for the electron effective mass parameter and we estimate the upper limit of the possible effective mass anisotropy is 7$\%$. We discuss the influence of band nonparabolicity on the electron effective mass parameter as a function of In content. The effective mass parameter is consistent with a linear interpolation scheme between the conduction band mass parameters in GaN and InN when the strong nonparabolicity in InN is included. The In${}_{0.33}$Ga${}_{0.67}$N electron mobility parameters were found to be anisotropic supporting previous experimental findings for wurtzite-structure GaN, InN, and Al${}_x$Ga${}_{1-x}$N epitaxial layers with $c$-plane growth orientation.

5 pages, 3 figures, 1 table