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In this work, we present the characterization of red InGaN/GaN multiple-quantum-well (MQW) light-emitting diode structures. The optical properties of two MQW structures with different n-GaN underlayer thicknesses (4 and 8 μm) are studied and compared. The results of photoluminescence studies show that a thicker n-GaN layer is beneficial for obtaining higher In content for red MQWs. However, the sample with a thicker n-GaN layer has a poorer internal quantum efficiency, a larger full width at half maximum, and a shorter nonradiative recombination time, implying that there are stronger In-content fluctuations and more defects. Furthermore, red MQWs with higher In content are shown to exhibit more deep localized states. Our findings imply that in order to achieve high-efficiency InGaN MQWs for red emission, enhancing the uniformity of In-content distribution in the active region and decreasing nonradiative recombination centers are critical challenges. [ABSTRACT FROM AUTHOR]

GaN/GaInN asymmetric multiple quantum well light-emitting diodes with varying potential barrier thicknesses (5 and 15 nm) are grown by using metal organic chemical vapor deposition. The narrow barrier structure improves the performance of the device, including the super-linear increase of electroluminescence integral intensity, the mitigation of efficiency droop at high current density, the reduction of wavelength drift, the reduction of forward voltage, and the improvement of wall-plug efficiency. This is due to the narrowing of the thickness of the quantum barrier, which results in the smaller electric field among the quantum well, the weakening of the quantum confinement Stark effect, the more uniform distribution of carriers across the active region of the device, and the suppression of electron leakage. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) characteristics of the structure consisting of green InGaN/GaN multiple quantum wells (MQWs) and low indium content InGaN/GaN pre-wells are investigated. Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed. The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature. In addition, the differences in the carrier localization effect, defect density, and phonon–exciton interaction between the pre-wells and green InGaN/GaN MQWs, and the internal quantum efficiency of the sample are studied. The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells. [ABSTRACT FROM AUTHOR]

Ultralow lasing threshold of $413~\mu \text{J}$ /cm2 in GaN-based vertical-cavity surface-emitting lasers (VCSELs) was observed by reducing the cavity lengths between double-side dielectric distributed Bragg reflectors to $6\lambda $. To the best of our knowledge, the threshold is the lowest value ever reported in nitride optically pumped VCSEL. The spontaneous emission factor ( $\beta $ ) was 0.1, and the degree of polarization was 91%. Effects of short cavity on spontaneous emission factors, gain coefficient enhancement, and absorption reduction were analyzed. In addition, effects of coupled quantum wells on the confinement factor were also discussed. We believe that our results would be meaningful for refining nitride VCSEL structure in the future. [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum wells (MQWs) are grown on (0001) sapphire substrates by metal organic chemical vapor deposition (MOCVD) with special growth parameters to form V-shaped pits simultaneously. Measurements by atomic force microscopy (AFM) and transmission electron microscopy (TEM) demonstrate the formation of MQWs on both (0001) and ( $$ 1\overline{1}01 $$) side surface of the V-shaped pits. The latter is known to be a semi-polar surface. Optical characterizations together with theoretical calculation enable us to identify the optical transitions from these MQWs. The layer thickness on ( $$ 1\overline{1}01 $$) surface is smaller than that on (0001) surface, and the energy level in the ( $$ 1\overline{1}01 $$) semi-polar quantum well (QW) is higher than in the (0001) QW. As the sample temperature is increased from 15 K, the integrated cathodoluminescence (CL) intensity of (0001) MQWs increases first and then decreases while that of the ( $$ 1\overline{1}01 $$) MQWs decreases monotonically. The integrated photoluminescence (PL) intensity of (0001) MQWs increases significantly from 15 to 70 K. These results are explained by carrier injection from ( $$ 1\overline{1}01 $$) to (0001) MQWs due to thermal excitation. It is therefore concluded that the emission efficiency of (0001) MQWs at high temperatures can be greatly improved due to the formation of semi-polar MQWs. [ABSTRACT FROM AUTHOR]

We fabricated GaN-based blue resonant-cavity light-emitting diodes (RCLEDs) by inserting InGaN quantum well (QW) active region between two dielectric distributed Bragg reflectors (DBRs). Due to the different gain enhancement factors in a single device, multi-longitudinal modes were observed and tuned with changing the injection current density: pure-blue (PB) at low current density, violet-blue (VB) at intermediate current density, and PB again at high current density. The variation of emission spectra is explained by the competition between band-filling effect and self-heating effect. • By using a resonant cavity design, the carrier localization in QWs is enhanced. • A localization model is proposed to describe the carrier transport. • The different gain enhancement factors cause the mode enhancement or suppression. • The emission spectrum is tuned due to the band-filling effect and heating effect. [ABSTRACT FROM AUTHOR]