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InN films with electron concentration ranging from n∼1017 to 1020 cm−3 grown by metal–organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated by variable-temperature photoluminescence and absorption measurements. The energy positions of absorption edge as well as photoluminescence peak of these InN samples with electron concentration above 1018 cm−3 show a distinct S-shape temperature dependence. With a model of potential fluctuations caused by electron-impurity interactions, the behavior can be quantitatively explained in terms of exciton freeze-out in local potential minima at sufficiently low temperatures, followed by thermal redistribution of the localized excitons when the band gap shrinks with increasing temperature. The exciton localization energy σloc is found to follow the n5/12 power relation, which testifies to the observed strong localization effects in InN with high electron concentrations. [ABSTRACT FROM AUTHOR]

We investigated the polarization and temperature dependence of photoluminescence (PL) of m-plane GaN grown on γ-LiAlO2 (100) substrate. The calculated electronic band structure with k•p Hamiltonian points out the energy splitting as well as polarization selection originate from the m-plane GaN epilayer under anisotropic strain. The polarization-angle dependence PL spectra are found to be selected from in-plane x- and z-polarized emission, corresponding to T1 and T2 transition. And the intensity distribution of the fitting peaks satisfies the Malus’ law. An S-shape energy evolution of near band edge peak on temperatures is observed, which originates from the transition between the localized holes and electrons in triangular potentials induced by basal stacking faults. [ABSTRACT FROM AUTHOR]

The effects of anisotropic strain on wurtzite GaN valence subbands are investigated both theoretically and experimentally. k•p perturbation theory reveals that the in-plane asymmetric strain not only affects the transition energies, but also determines the polarization properties, which is analyzed to be the essential cause of the optical anisotropy. Considerable in-plane anisotropy of strained C-plane GaN in polarized photoluminescence is reported. The experimental result in good agreement with theoretical study directly proves the strain effects on the transitions polarization states. The fine accordance of observed and simulated photoluminescence dependences on strain asymmetry degree demonstrates a primary realization of strain controlled optical anisotropy, and such modulation indicates the great potential of utilizing GaN-based semiconductors in polarization-sensitive optoelectronics. [ABSTRACT FROM AUTHOR]