The energy relaxation of InN thin films has been studied by ultrafast time-resolved photoluminescence technique. The obtained carrier cooling curves can be explained by carriers releasing excessive energy through the carrier–LO-phonon interaction. The extracted effective phonon emission times decrease as the photoexcited carrier concentration reduces and come close to the theoretical prediction of 23fs at small carrier concentration. The reduction of energy loss rate at high photoexcited carrier density is attributed to the hot phonon effect.

Auger recombination is studied in InN thin films using an ultrafast time-resolved photoluminescence apparatus. The decay rates are analyzed with nonlinear dependence of the photoluminescence intensity on the carrier concentration. The fitted radiative recombination coefficients at a temperature of 35K are consistent with the theoretical prediction. The Auger rates are small at low carrier concentrations but increase quadratically with the carrier concentration. The Auger activation energies of 4.3 and 9.0meV obtained from the temperature-dependent Auger coefficient indicate that Auger recombination is weakly dependent on temperature and is a phonon-assisted process.

Time-integrated and time-resolved photoluminescence (PL) of InN thin films of different background carrier concentrations are investigated. The PL formation mechanism is attributed to the “free-to-bound” transition by analyzing the time-integrated PL spectra at different pump fluences. The dependence of the PL decay time with emission energy is investigated using a theoretical model which speculates upon the carrier localization in InN thin films. The radiative lifetime, mobility edge, and carrier localization energy are obtained from the dependence of the PL decay time on emission energy and are studied at different background carrier concentrations. The effect of intervalley scattering between the Γ1 and Γ3 valley on the radiative lifetime, mobility edge, and carrier localization energy is discussed. The longer radiative lifetime and smaller values of the mobility edge and localization energy for 3.06 eV excitation are observed than that for the 1.53 eV excitation due to the intervalley scattering process.

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