We report on the study of plasma edge absorption of InN epilayers with free electron concentration ranging from 3.5×1017to5×1019cm−3. Together with the previously reported data, the wide range variation of effective mass cannot be explained by Kane’s two band k∙p model alone. We show that the combination of Kane’s two band k∙p model, band renormalized effect due to electron–electron interaction, and electron–ionized impurity interaction can provide an excellent description. The effective mass of the free electron at the bottom of the conduction band was found to be m*=0.05m0, which is in good agreement with the very recent theoretical calculation.

We report a detailed investigation of the photoluminescent properties of InN epifilms with free-electron concentrations ranging from 3.5 × 10 17 cm −3 to 5 × 10 19 cm −3 . It is found that the photoluminescence (PL) peak energy strongly depends on the electron concentration. We show that the broadening of the PL spectra with increasing free-electron concentration arises from the breaking of the k = 0 selection rule. The large asymmetric line shape of the photoluminescence spectra can be well described by the free-electron recombination band model. We establish an empirical relation between the full-width at half-maximum (FWHM) value of the PL spectra and the free-electron concentration, which provides a convenient formula to determine the free-electron concentration in InN epifilms by PL measurement. We point out that the peak energy of the PL spectra does not reflect the real band gap of InN epifilms. Calculations based on the effects of Burstein-Moss absorption, band tail and band renormalization were used to analyse the PL spectra, and the fundamental band gap of the intrinsic InN film was obtained. The corresponding expression for the band gap narrowing effect of the InN film is found to be E BGN = 1 × 10 −8 n 1/3 + 3.6 × 10 −7 n 1/4 + 2.3 × 10 −11 n 1/2 eV. The temperature-dependent band gap of the intrinsic InN was fitted by the Pässler equation. The Pässler parameters of the intrinsic InN are α = 0.55 meV K −1 , = 576 K and p = 2.2. It is found that the band gap energies at T = 0 K and room temperature are close to 0.68 eV and 0.62 eV, respectively. In addition, we show that the band gap obtained from the PL spectra is in excellent agreement with that obtained from infrared absorption.

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A novel phenomenon called the photoelastic effect had been observed in ZnO nanorods, along with a number of intriguing anomalies. With increasing excitation power, it was found that the A 1 (LO) phonon exhibited a red-shift in frequency, on top of a blue-shift in the photoluminescence (PL) peak energy. In addition, the temperature-dependent photoluminescence spectra behaved quite differently under high and low excitation power. All our results can be accounted for by the photoelastic effect, in which the built-in surface electric field was screened by photoexcited electrons and holes. Through the converse piezoelectric effect, the internal strain was therefore altered. Our results make possible a new thrust for manipulating the physical properties of ZnO nanorods, and should prove very useful in the application of optoelectric devices.