Electron Mobility in Polarization-doped Al${}_{0-0.2}$GaN with a Low Concentration Near 10${}^{17}$ cm${}^{-3}$

Abstract

In this letter, carrier transport in graded Al${}_{\mathrm{x}}$Ga${}_{1-\mathrm{x}}$N with a polarization-induced n-type doping as low as ~ 10${}^{17}$ cm${}^{-3}$ is reported. The graded Al${}_{\mathrm{x}}$Ga${}_{1-\mathrm{x}}$N is grown by metal organic chemical vapor deposition on a sapphire substrate and a uniform n-type doping without any intentional doping is realized by linearly varying the Al composition from 0% to 20% over a thickness of 600 nm. A compensating center concentration of ~10${}^{17}$ cm${}^{-3}$ was also estimated. A peak mobility of 900 cm${}^2$/V$\cdot$s at room temperature is extracted at an Al composition of ~ 7%, which represents the highest mobility achieved in n-Al${}_{0.07}$GaN with a carrier concentration ~10${}^{17}$ cm${}^{-3}$. Comparison between experimental data and theoretical models shows that, at this low doping concentration, both dislocation scattering and alloy scattering are significant in limiting electron mobility; and that a dislocation density of <10${}^7$ cm${}^{-2}$ is necessary to optimize mobility near 10${}^{16}$ cm${}^{-3}$. The findings in this study provide insight in key elements for achieving high mobility at low doping levels in GaN, a critical parameter in design of novel power electronics taking advantage of polarization doping.

6 figures. Submitted to Applied Physics Letters