Mobility in epitaxial GaN: Limitations of free-electron concentration due to dislocations and compensation

Abstract

A detailed numerical description of the free-electron concentration and mobility due to charged dislocation lines is presented. The scattering at dislocations is numerically analyzed in addition to the other scattering mechanisms and the transverse mobility is calculated by the energy averaging technique. Furthermore, the effect on mobility from an unintentional bulk acceptor concentration is calculated at room temperature. Specifically the calculated mobility is presented as a function of the combined effect from free electrons ${(10}^{15}--{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}),$ dislocations $(5\ifmmode\times\else\texttimes\fi{}{10}^{8}--{10}^{12}{\mathrm{cm}}^{\ensuremath{-}2}),$ and bulk acceptors ${(10}^{15}--{10}^{19}{\mathrm{cm}}^{\ensuremath{-}3}).$ Also compensation from 0 to 100% is considered. Results are compared with experimental mobility data. Most mobility results in epitaxially grown GaN layers intended for optical and electronic device structures are limited by $\ensuremath{\sim}{10}^{10}{\mathrm{cm}}^{\ensuremath{-}2}$ dislocations and a compensation which is typically 30%--60%.