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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]

Abstract: GaN-based light-emitting devices (LEDs) with and without a rear distributed Bragg reflector (DBR) were grown by metal–organic chemical vapor deposition. The integrated electroluminescence (EL) intensity of LED with a rear nitride DBR showed a super-linear increase up to a current density of 135A/cm2 and the relative external quantum efficiency (EQE) kept monotonously increasing with increase in injection current density. For the LED without a rear DBR, however, the emission efficiency reached the maximum at a very low current density of 10A/cm2. The improvement is mainly attributed to reflection of light from the DBR to the “top side” and decrease in light absorption in the active region with increase in injection current density. Moreover, the improvement in relative EQE was attributed to the resonant cavity enhancing spontaneous emission at its resonant wavelength too. [ABSTRACT FROM AUTHOR]

In diffusion to blue light-emitting diode (LED) wafers is performed by the inductive coupled plasma (ICP) treatment of a covering layer of indium tin oxide (ITO) on the wafer surface. The electrical property of the p-type contact is improved and the redshift of photoluminescence (PL) from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy (XPS) demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20 mA, LEDs with ICP-induced In doping show a decrease of 0.3V in the forward voltage and an increase of 23% in the light output, respectively. [ABSTRACT FROM AUTHOR]

Optical and electrical properties of InGaN/GaN multiple quantum wells (MQWs) light emitting diodes (LEDs) annealed in pure O2 ambient (500°C) and pure N2 ambient (800°C) were systematically investigated. The temperature-dependent photoluminescence measurements showed that high-temperature thermal annealing in N2 ambient can induce indium clusters in InGaN MQWs. Although the deep traps induced by indium clusters can act as localized centers for carriers, there are many more dislocations out of the trap centers due to high-temperature annealing. As a result, the radiative efficiency of the sample annealed in N2 ambient was lower than that annealed in O2 ambient at room temperature. Electrical measurements demonstrated that the LEDs annealed in O2 ambient were featured by a lower forward voltage and there was an increase of ~41% in wall-plug efficiency at 20mA in comparison with the LEDs annealed in N2 ambient. It is thus concluded that activation of the Mg-doped p-GaN layer should be carried out at a low-temperature O2 ambient so as to obtain LEDs with better performance. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature Sn fusion bonding technique was proposed to fabricate GaN-based blue vertical light-emitting diodes (LEDs) on Si substrate. First, by studying photoluminescence (PL) spectra of GaN LED epilayers/Ag-based mirror/Si structures fabricated at different bonding temperatures, it was confirmed that the quality of Ag-based mirror was not degraded when the bonding temperature was 250°C. Then GaN-based blue vertical LEDs were fabricated at this bonding temperature. As compared with conventional GaN-based LEDs, the vertical LEDs revealed improved forward current–voltage characteristic, especially, the reverse current of the vertical LEDs was as low as 39nA at the reverse bias of −10V. In the mean time, vertical LEDs showed an increase in light output of about 127% at 200mA, and no saturation was observed as the driving current increased to 500mA. Further measurement revealed that vertical LEDs had a much lower junction temperature. These results indicate that the Sn fusion bonding technique is an effective way for fabrication of high-power GaN-based LEDs. [Copyright &y& Elsevier]

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]