Optical properties of gallium nitride bulk crystals grown by chloride vapor phase epitaxy

Abstract

The optical properties of bulk crystals of gallium nitride grown by chloride vapor-phase epitaxy are investigated. It is shown that these crystals exhibit exciton luminescence bands. Analysis of the energy positions of the band maxima imply certain conclusions about the presence or absence of mechanical stresses in the bulk crystals of GaN obtained. Analysis of the luminescence spectra also reveals that the temperature dependence of the width of the GaN band gap E g in the temperature range T=6–600 K is well described by the expression E g (T)=3.51−7.4×10−4 T 2(T+600)−1 eV. It is estimated that values of the free electron concentration in these crystals do not exceed 1018 cm−3. The optical characteristics of the bulk GaN crystals are compared analytically with literature data on bulk crystals and epitaxial layers of GaN grown by various methods.