Effects of phonon coupling and free carriers on band-edge emission at room temperature in n-type ZnO crystals

Abstract

Room-temperature photoluminescence has been studied in n-type bulk ZnO crystals representing three different growth methods and having free-carrier concentrations (n) ranging from 1013to1018cm−3. The near-band-edge emission has both free-exciton and free-exciton-phonon contributions, with the strength of the phonon coupling dependent on sample defect concentrations. Band-gap shrinkage effects are used to explain a decrease in emission energy for the higher n values. Band filling and band nonparabolicity are predicted to be important for n>1019cm−3. At 300K, in the absence of free carriers, the free-exciton energy is 3.312±0.004eV.