KEYWORDS: Quantum wells, Luminescence, Heterojunctions, Optical properties, Temperature metrology, Indium, Aluminum, Nanostructures, Crystals, Chemical species
The anomalous Berthelot-type optical properties of quaternary AlInGaN heterostructure with different quantum well pairs have been systematically investigated in this study. The Berthelot-type model refers to the temperature dependence of emission intensity with blue then red shift behavior in disorder material system. The photoluminescence of the AlInGaN heterostructures is also found to exhibit such unique luminescence features as S-shaped emission peak energy similar to Berthelot-type properties over temperature. We ascribed the phenomenon to the spinodal decompositions, which will lead to the appearance of the Berthelot-type behavior. The increase of quantum well pairs will cause the incorporation of indium and/or aluminum atoms in the AlInGaN nanostructures more obviously, resulting in augmentation of the degree of crystalline randomization. In other words, the higher degree of disorder in AlInGaN heterostructures is observed to manifest not only the extension of static microbarrier width, but also the enhancement of carrier localization effects.
Nitride-based light-emitting diodes (LEDs) have recently attracted to understand the emission mechanisms in
novel multiple quantum well (MQW) heterosturctures. To understand substantially the unique spectral response, it is
necessary to examine the carrier transport behavior. In this work, we studied the unique correlations between the carrier
dynamics and optical characteristics of the quaternary AlInGaN MQW heterostructures with different barrier widths. It
has been found that the photoluminescence peak energy of quaternary AlInGaN MQW blueshifts when decreasing the
barrier width. This is attributed to the redistribution among the well and barrier of the strong electrostatic fields induced
by polarization effect. It resulted in not only the diminutions of the charge density induced by piezoelectric field, but also
the increments of the interface-state charge distribution from the collective influence of alloy disorder and interface
roughness. We resort the Arrhenius plots to demonstrate the localized effect originated from indium fluctuation. Our
results show the exciton-localization effect can be enhanced monotonically by increasing the barrier widths. On the other
hand, we corroborated the surface charge density increased while increasing barrier widths between the epitaxial layers
in this investigation.
Major developments in group-III nitride semiconductors have led to the commercial production of InGaN-based blue/green multiple quantum well (MQW) laser diodes (LDs) and light-emitting diodes (LEDs) for use in varied applications. The main approaches have been adopted to meet the increasing demands for improved efficiency in modern optoelectronic devices; enhancing the light extraction and the quantum efficiency. In this work, the improvement of carrier localization confinement in InGaN/GaN multiple quantum well structures has been achieved by introducing hydrogen-flow treatment into the growth procedures. To characterize the radiative recombination mechanisms in the active layers, the temperature-dependent photoluminescence (PL) of InGaN/GaN MQW structures have been measured.
It has been found the strong temperature-dependent blueshift of the emission peak energy for the conventional MQW sample due to band filling effect. As the temperature increased, for the MQW sample with hydrogen-flow treatment, it has been found the emission peak of PL spectra exhibited an obvious red-blue-red shift, i.e., S-shaped shift. By introduction of hydrogen flow during the growth procedures, it has been expected not only to encourage atom coherence motions tend to three-dimension cluster formations but also to provide a stronger localization confinement ability to enhance exciton radiative recombinations in the band tail of the density of states. From the Arrhenius plot of PL intensity, compared with the value of 120 meV achieved for the conventional MQW sample, the higher activation energy value of 300 meV for the MQW sample with hydrogen-flow treatment implies that there was better confinement ability for the excess charge carriers.
In this work, thermal effects on the optoelectrical characteristics of green InGaN/GaN multiple quantum well
(MQW) light-emitting diodes (LEDs) have been investigated in detail for a broad temperature range, from 30oC to 100oC. The current-dependent electroluminescence (EL) spectra, current-voltage (I-V) curves and luminescence-current (L-I)
curve have been measured to characterize the thermal-related effects on the optoelectrical properties of the InGaN/GaN
MQW heterostructures. Experimentally, both the forward voltages decreased with slope of -2.6 mV/K and the emission
peak wavelength increased with slope of +4.5 nm/K with increasing temperature, indicating a change in the contact
resistance between the metal and GaN layers and the band gap shrinkage effect. With increasing injection current, it has
been found the strong current-dependent blueshift of -0.048 nm/mA in EL spectra. It was attributed to not only the
stronger band-filling effect but also the enhanced quantum confinement effect, resulted from the piezoelectric
polarization and the spontaneous polarization in InGaN/GaN heterostructures. The junction temperature calculated by
forward voltage was from 25.6 to 14.5oC and by emission peak shift was from 22.4 to 35.6oC.
In this article, we investigate the anomalous temperature characteristics of InGaN/GaN multiple quantum-well (MQW) blue light emitting diodes (LEDs), with multiquantum barriers (MQBs) and GaN barriers, in depth via an examination of the luminescence intensity and carrier transport temperature evolution. The experimental evidences for electrical properties of two diodes exhibited the ideality factor extremely departure from unity, and the anomalies were characterized by pseudo-temperature To and carrier tunneling behavior. With respect to conventional GaN barrier devices, devices with MQBs inherently exhibit a small pseudo-temperature To with a small characteristic energy and charge population of the multilayer interface, over a variety of temperature and voltage ranges. Due to the less interface state distribution and the more effective density of state (DOS), the excitons formed in the MQB sample augment the spectral radiations at the temperature higher than 180 K. Furthermore, the carrier tunneling processes via the extent of the charge population consequently cause anomaly more To and further characteristic energy, result in the abnormal deterioration of the EL intensities with small DOS for these two LEDs below 180 K. These results also demonstrate that an introduction of well-designed barriers within a heterojunction configuration can be used to perform device improvements by governing the coupling of dynamical transports to spontaneous emissions. All observed correlations suggest that the carrier transport process is essentially responsible for the improvement of the luminescence characteristic. Accordingly, the MQW with the well-designed MQB structures not only exhibited the thermal-insensitive luminescence, but also inhibited the energetic carrier overflow.
Temperature-dependent electroluminescence (EL) of blue InGaN/GaN multiquantum-well light-emitting diodes (LEDs) has been systematically investigated to illustrate the role of multiquantum barrier (MQB) in carrier capture and recombination. With recent advances in nitride-based light-emitting diodes (LEDs), the importance for the development of high brightness as well as high temperature devices is profound. It is found that, when temperature is slightly decreased to 200 K, the EL intensity of the active region efficiently increases in both devices, as usually seen due to the improved quantum efficiency. However, with further decrease of temperature down to 20 K, unusual reduction of the integrated EL intensity of the active region is commonly observed for both of the two diodes, accompany with the appearance of the high energy band which can be assigned as Mg-related transition at relative low temperature. It also clear noted the the diode without MQB shows a faster reduction tendency of the EL intensity than the one with MQB. Based on a rate equation analysis, we found that not only the radiative recombination zone of the quantum well region less shift to the p-type GaN region for device with MQB, but also the intensity of Mg-related transition in the LED with MQB are more than one order of magnitude less than the one without MQB. These results further verify the effective carrier confinement in active region, less carrier leakage over the barrier, and improvement of the luminescence efficiency by MQBs. All the calculations are agreement with the experimental observations.
We present results concerning the influence of organometrallic vapro phase epitaxy (OMVPE) grwoth paramters under ultra low V/III ratio on the surface morphology and temperature-dependent photoluminescence. Due to Indium segregation inteh 2D InAs wetting layers and accumulation from multi-atomic step edge on (001) 2° off toward (111) n-type GaAs substrate, self-assembled InAs quatnum dot formation takes pace aroudn or above 2D InAs islands while ~ one monolayer of InAs is regularly grown on GaAs substrate. It is attributed that the desorbed Indium Recaptured and nucleated effect on edge along (110)-orientation of GaAs substrate.
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