Recombination Pathways in Green InGaN/GaN Multiple Quantum Wells (original) (raw)
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Two-Component Photoluminescence Decay in InGaN/GaN Multiple Quantum Well Structures
Physica Status Solidi B-basic Solid State Physics, 2001
Two-component decay of time-resolved photoluminescence (TRPL) intensity in three InGaN/GaN multiple quantum well samples were observed. The first-decay component was attributed to exciton relaxation of free-carrier and localized states; the second-decay one was dominated by the relaxation of localized excitons. The second-decay lifetime was related to the extent of carrier localization or indium aggregation and phase separation. The lifetime of free-carrier states was connected with the defect density. Based on the temperature-dependent data of PL and stimulated emission (SE), the localization energies of the three samples were calibrated to show the consistent trend with the second-decay lifetime and previous material analyses.
Optics Express, 2012
Excitation power and temperature dependences of the photoluminescence (PL) spectra are studied in InGaN/GaN multiple quantum wells (MQWs). The excitation power dependences of the PL peak energy and linewidth indicate that the emission process of the MQWs is dominated first by the Coulomb screening effect and then by the localized states filling at low temperature, and that the nonradiative centers are thermally activated in low excitation range at room temperature. The anomalous temperature dependences of the peak energy and linewidth are well explained by the localized carrier hopping and thermalization process, and by the exponentially increased density of states with energy in the band tail. Moreover, it is also found that internal quantum efficiency is related to the mechanism conversion from nonradiative to radiative mechanism, and up to the carriers escaping from localized states.
Journal of Microscopy, 2017
In this work, we analyse the microstructure and local chemical composition of green-emitting In x Ga 1-x N/GaN quantum well (QW) heterostructures in correlation with their emission properties. Two samples of high structural quality grown by metalorganic vapour phase epitaxy (MOVPE) with a nominal composition of x = 0.15 and 0.18 indium are discussed. The local indium composition is quantitatively evaluated by comparing scanning transmission electron microscopy (STEM) images to simulations and the local indium concentration is extracted from intensity measurements. The calculations point out that the measured indium fluctuations may be correlated to the large width and intensity decrease of the PL emission peak.
Applied Physics Letters, 2002
Based on wavelength-dependent and temperature-varying time-resolved photoluminescence ͑PL͒ measurements, the mechanism of carrier transport among different levels of localized states ͑spatially distributed͒ in an InGaN/GaN quantum well structure was proposed for interpreting the early-stage fast decay, delayed slow rise, and extended slow decay of PL intensity. The process of carrier transport was enhanced with a certain amount of thermal energy for overcoming potential barriers between spatially distributed potential minimums. With carrier supply in the carrier transport process, the extended PL decay time at wavelengths corresponding to deeply localized states can be as large as 80 ns.
By means of time-resolved photoluminescence (PL) and confocal PL measurements, temporally and spatially resolved optical properties have been investigated on a number of In x Ga 1Àx N/GaN multiple-quantum-well (MQW) structures with a wide range of indium content alloys from 13% to 35% on ð11 22Þ semi-polar GaN with high crystal quality, obtained through overgrowth on nanorod templates. With increasing indium content, the radiative recombination lifetime initially increases as expected, but decreases if the indium content further increases to 35%, corresponding to emission in the green spectral region. The reduced radiative recombination lifetime leads to enhanced optical performance for the high indium content MQWs as a result of strong exciton localization, which is different from the behaviour of c-plane InGaN/GaN MQWs, where quantum confined Stark effect plays a dominating role in emission process. V
Journal of Applied Physics, 2004
We have examined in detail the optical properties of InGaN quantum wells ͑QWs͒ grown on pyramidal GaN mesas prepared by lateral epitaxial overgrowth ͑LEO͒ in a metalorganic chemical vapor deposition system that resulted in QWs on ͕1-101͖ facets. The effects of In migration during growth on the resulting QW thickness and composition were examined with transmission electron microscopy ͑TEM͒ and various cathodoluminescence ͑CL͒ imaging techniques, including CL wavelength imaging and activation energy imaging. Spatial variations in the luminescence efficiency, QW interband transition energy, thermal activation energy, and exciton binding energy were probed at various temperatures. Cross-sectional TEM was used to examine thickness variations of the InGaN/GaN QW grown on a pyramidal mesa. CL imaging revealed a marked improvement in the homogeneity of CL emission of the LEO sample relative to a reference sample for a conventionally grown In 0.15 Ga 0.85 N/GaN QW. The characteristic phase separation that resulted in a spotty CL image profile and attendant carrier localization in the reference sample is significantly reduced in the LEO QW sample. Spatial variations in the QW transition energy, piezoelectric field, and thermal activation energy were modeled using excitonic binding and transition energy calculations based on a single-band, effective-mass theory using Airy function solutions. Band-edge and effective-mass parameters were first obtained from a strain-and In-composition-dependent k"p calculation for wurtzite In x Ga 1Ϫx N, using a 6ϫ6 k"p Hamiltonian in the ͕1-101͖ representations. The calculations and experiments confirm a facet-induced migration of In during growth, which results in a smooth compositional variation from xϷ0.10 at the bottom of the pyramid to x Ϸ0.19 at the top. We demonstrate the existence of a strong correlation between the observed thermal activation behavior of QW luminescence intensity and the associated exciton binding energy for various positions along the pyramidal InGaN/GaN QWs, suggesting exciton dissociation is responsible for the observed temperature dependence of the QW luminescence in the ϳ150 to 300 K range.
Characterization of high-quality InGaN/GaN multiquantum wells with time-resolved photoluminescence
Applied Physics Letters, 1998
Recombination in single quantum well and multiquantum well InGaN/GaN structures is studied using time-resolved photoluminescence and pulsed photoluminescence measurements. Room-temperature measurements show a rapid lifetime ͑0.06 ns͒ for a single quantum well structure, while an increasingly long decay lifetime is measured for multiquantum wells as more quantum wells are incorporated into the structure. Temperature-dependent lifetime measurements show that a nonradiative recombination mechanism activates above 45 K in the single quantum well but is less important in the multiquantum wells.
Solid State Communications, 2001
The effects of Si doping on the optical properties and recombination dynamics of InGaN/GaN multiple quantum wells (MQWs) has been investigated by means of photoluminescence (PL) and time-resolved PL (TRPL) measurements. The peak energies and the full width at half maximum (FWHM) values of both the stimulated emission and spontaneous emission increase with increasing Si doping concentration. The PL spectrum consisting of three (or two) Gaussian peaks was interpreted by the results of the TRPL. These PL emission peaks have three (or two) different origins (i.e., different decay times) of the ®rst (t 1 ), the second (t 2 ), and the third (t 3 ) PL emission. The redshift of the emission peak with delay time and the increase of the emission peak energies and the FWHMs with increasing Si doping concentration are attributed to the band ®lling of localized states. q