We report temperature-dependent time-integrated and time-resolved photoluminescence (PL) studies of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous emission behavior, specifically an S-shaped (decrease–increase–decrease) temperature dependence of the peak energy (Ep) for InGaN-related PL with increasing temperature: Ep redshifts in the temperature range of 10–70 K, blueshifts for 70–150 K, and redshifts again for 150–300 K with increasing temperature. In addition, when Ep redshifts, the spectral width is observed to narrow, while when Ep blueshifts, it broadens. From a study of the integrated PL intensity as a function of temperature, it is found that thermionic emission of photocarriers out of local potential minima into higher energy states within the wells is the dominant mechanism leading to the thermal quenching of the InGaN-related PL. We demonstrate that the temperature-induced S-shaped PL shift is caused by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the InGaN/GaN MQWs.
We present a comprehensive study of the optical characteristics of Al x Ga 1Ϫx N epilayers (0рxр0.6) by means of photoluminescence ͑PL͒, PL excitation, and time-resolved PL spectroscopy. For Al x Ga 1Ϫx N with large Al content, we observed an anomalous PL temperature dependence: ͑i͒ an ''S-shaped'' PL peak energy shift ͑decrease-increase-decrease͒ and ͑ii͒ an ''inverted S-shaped'' spectral width broadening ͑increasedecrease-increase͒ with increasing temperature. We observed that the thermal decrease in integrated PL intensity was suppressed and the effective lifetime was enhanced in the temperature region showing the anomalous temperature-induced emission behavior, reflecting superior luminescence efficiency by suppressing nonradiative processes. All these features were enhanced as the Al mole fraction was increased. From these results, the anomalous temperature-induced emission shift is attributed to energy tail states due to alloy potential inhomogeneities in the Al x Ga 1Ϫx N epilayers with large Al content.
Articles you may be interested inOptical study of a -plane InGaN/GaN multiple quantum wells with different well widths grown by metal-organic chemical vapor deposition J. Appl. Phys.
Optical absorption measurements were performed on a series of thin GaN epilayers. Sharp spectral features were observed due to the 1s A and B exciton transitions. Using polarization dependent absorption, the C exciton transition was identified. A broad absorption feature was observed at ϳ3.6 eV, which is attributed to indirect exciton-phonon absorption. The excitonic structure was found to persist well above room temperature. A fit to the Varshni formula yielded a temperature dependence of E(T)ϭE(Tϭ0)Ϫ11.8ϫ10 Ϫ4 T 2 (1414ϩT) eV for the A and B excitons. The exciton absorption linewidth was studied as a function of temperature, indicating that GaN exhibits very large exciton-phonon coupling.
Negative differential resistance associated with hot phonons J. Appl. Phys. 112, 063707 (2012) Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method J. Appl. Phys. 112, 063109 (2012) Optical properties of InGaPN epilayer with low nitrogen content grown by molecular beam epitaxy J. Appl. Phys. 112, 063507 (2012) Residual compressive stress induced infrared-absorption frequency shift of hexagonal boron nitride in cubic boron nitride films prepared by plasma-enhanced chemical vapor deposition J. Appl. Phys. 112, 053502 (2012) Spontaneous emission and optical gain characteristics of blue InGaAlN/InGaN quantum well structures with reduced internal fieldWe present the results of optical studies of the properties of In x Ga 1Ϫx N epitaxial layers (0Ͻx Ͻ0.2) grown by metalorganic chemical vapor deposition. The effects of alloying on the fundamental band gap of In x Ga 1Ϫx N were investigated using a variety of spectroscopic techniques. The fundamental band-gap energies of the In x Ga 1Ϫx N alloys were determined using photomodulation spectroscopy measurements and the variation of the fundamental band gap was measured as a function of temperature. The effects of pressure on the band gap for In x Ga 1Ϫx N samples with different alloy concentrations were examined by studying the shift of photoluminescence ͑PL͒ emission lines using the diamond-anvil pressure-cell technique. The results show that PL originates from effective-mass conduction-band states. Anomalous temperature dependence of the PL peak shift and linewidth as well as the Stokes shift between photoreflectance and PL lines is explained by composition fluctuations in as-grown InGaN alloys.
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