Carrier localization of as-grown n-type gallium nitride under large hydrostatic pressure.

Abstract

A quantitative study of the carrier localization in GaN under large hydrostatic pressure is presented using infrared reflection and Raman spectroscopy. The free-carrier concentration in as-grown n-type GaN crystals is determined optically from the phonon-plasmon--coupled mode and an analysis of the dielectric function. A strong decrease from 1\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at ambient pressure to only 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ at a pressure of 27 GPa is observed. This free-carrier reduction is attributed to a strongly localized donor present at a concentration of 1\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and it is in agreement with previous qualitative results. From our quantitative data we determine the position of the neutral-donor level to be ${126}_{\mathrm{\ensuremath{-}}5}^{+20}$ meV below the conduction band at 27 GPa. We present a model for the pressure dependence of the localized defect and predict its neutral level at 0.40\ifmmode\pm\else\textpm\fi{}0.10 eV above the conduction-band edge at ambient pressure. \textcopyright{} 1996 The American Physical Society.