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

The optical properties of bulk crystals of gallium nitride grown by chlorid e vapor-phase epitaxy are investigated. It is shown that these crystals exh ibit exciton luminescence bands. Analysis of the energy positions of the ba nd maxima imply certain conclusions about the presence or absence of mechan ical stresses in the bulk crystals of GaN obtained. Analysis of the lumines cence 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 b y the expression E-g(T)=3.51-7.4x10(-4) T-2(T+600)(-1) eV. It is estimated that values of the free electron concentration in these crystals do not exc eed 10(18) 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. (C) 1999 American Institute of Phys ics. [S1063-7826(99)00510-4].