Effects of number of quantum wells and Shockley-Read-Hall recombination in deep-ultraviolet light-emitting diodes.

Effects of the number of quantum wells (QWs) and Shockley-Read-Hall (SRH) recombination in deep-ultraviolet (DUV) light-emitting diodes (LEDs) are investigated theoretically. Simulation results show that, for DUV LEDs with high crystalline quality, light output power increases with an increasing number of QWs. As for the DUV LEDs with poor crystalline quality, light output power may decrease with an increasing number of QWs due to the deteriorated SRH recombination.

Monolithic stacked blue light-emitting diodes with polarization-enhanced tunnel junctions.

Monolithic stacked InGaN light-emitting diode (LED) connected by a polarization-enhanced GaN/AlN-based tunnel junction is demonstrated experimentally in this study. The typical stacked LEDs exhibit 80% enhancement in output power compared with conventional single LEDs because of the repeated use of electrons and holes for photon generation. The typical operation voltage of stacked LEDs is higher than twice the operation voltage of single LEDs.

Reduced efficiency droop in blue InGaN light-emitting diodes by thin AlGaN barriers.

The phenomenon of efficiency droop in blue InGaN light-emitting diodes (LEDs) is studied numerically. Simulation results indicate that the severe Auger recombination is one critical mechanism corresponding to the degraded efficiency under high current injection. To solve this issue, LED structure with thin AlGaN barriers and without the use of an AlGaN EBL is proposed.

Numerical study of the suppressed efficiency droop in blue InGaN LEDs with polarization-matched configuration.

In blue InGaN light-emitting diodes (LEDs), the intuitive approaches to suppress Auger recombination by reducing carrier density, e.g., increasing the number of quantum wells (QWs) and thickening the width of wells, suffer from nonuniform carrier distribution and more severe spatial separation of electron and hole wave functions.

Investigation of InGaN green light-emitting diodes with chirped multiple quantum well structures.

The effect of using chirped multiple quantum-well (MQW) structures in InGaN green light-emitting diodes (LEDs) is numerically investigated. An active structure, which is with both thick QWs with low indium composition on the p-side and thin QWs with high indium composition next to the n-region, is presented in this study. The thickness and indium composition in each single QW is specifically tuned to emit the same green emission spectrum.

Influence of polarization-matched AlGaInN barriers in blue InGaN light-emitting diodes.

The advantages of blue InGaN light-emitting diodes with low bandgap energy and polarization-matched AlGaInN barriers are demonstrated numerically. Simulation results show that, besides the common benefit of enhanced electron-hole spatial overlap in the quantum well from the polarization-matched condition, the lower bandgap energy barriers can have additional advantages of more uniform carrier distribution among quantum wells while maintaining sufficient electron confinement. The internal quantum efficiencies of all the polarization-matched structures under study exhibit less severe efficiency droop, which is presumably attributed to the suppression of Auger recombination.

Numerical investigation on the enhanced carrier collection efficiency of Ga-face GaN/InGaN p-i-n solar cells with polarization compensation interlayers.

The impact of the polarization compensation InGaN interlayer between the heterolayers of Ga-face GaN/InGaN p-i-n solar cells is investigated numerically. Because of the enhancement of carrier collection efficiency, the conversion efficiency is improved markedly, which can be ascribed to both the reduction of the polarization-induced electric field in the InGaN absorption layer and the mitigation of potential barriers at heterojunctions. This beneficial effect is more remarkable in situations with higher polarization, such as devices with a lower degree of relaxation or devices with a higher indium composition in the InGaN absorption layer.

Enhancement in hole-injection efficiency of blue InGaN light-emitting diodes from reduced polarization by some specific designs for the electron blocking layer.

Some specific designs on the electron blocking layer (EBL) of blue InGaN LEDs are investigated numerically in order to improve the hole injection efficiency without losing the blocking capability of electrons. Simulation results show that polarization-induced downward band bending is mitigated in these redesigned EBLs and, hence, the hole injection efficiency increases markedly. The optical performance and efficiency droop are also improved, especially under the situation of high current injection.

Advantages of blue InGaN light-emitting diodes with AlGaN barriers.

The advantages of blue InGaN light-emitting diodes (LEDs) with AlGaN barriers are studied numerically. The performance curves, energy band diagrams, electrostatic fields, and carrier concentrations are investigated. The simulation results show that the InGaNAlGaN LED has better performance than its conventional InGaNGaN counterpart owing to the increase of hole injection and the enhancement of electron confinement.