RESUMEN
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. The injection current density is also an important factor regarding the impact of the number of QWs. When operated at low current density, for the DUV LED with poor crystalline quality, light output power may decrease with an increasing number of QWs.
RESUMEN
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. This high operation voltage can be attributed to the non-optimal tunneling junction in stacked LEDs. In addition to the analyses of experimental results, theoretical analysis of different schemes of tunnel junctions, including diagrams of energy bands, diagrams of electric fields, and current-voltage relation curves, are investigated using numerical simulation. The results shown in this paper demonstrate the feasibility in developing cost-effective and highly efficient tunnel-junction LEDs.
RESUMEN
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. The purpose of the strain-compensation AlGaN barriers is to mitigate the strain accumulation in a multiquantum well (MQW) active region in this thin-barrier structure. With the proposed LED structure, the hole injection and transportation of the MQW active region are largely improved. The carriers can thus distribute/disperse much more uniformly in QWs, and the Auger recombination is suppressed accordingly. The internal quantum efficiency and the efficiency droop are therefore efficiently improved.
RESUMEN
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. To resolve this issue, LED structures with thick InGaN wells and polarization-matched AlGaInN barriers are proposed theoretically. Furthermore, the number of QWs is reduced for the purpose of mitigating the additional compressive strain in AlGaInN barriers. Simulation results reveal that, in the proposed structures, the quantum-confined Stark effect in strained wells is nearly eliminated through the utilization of polarization-matched barriers, which efficiently promotes internal quantum efficiency. Furthermore, the phenomenon of efficiency droop is also markedly improved because of the uniformly distributed or dispersed carriers, and accordingly the suppressed Auger recombination.
RESUMEN
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. Comparing with conventional active structure design of green LEDs, which is using uniform MQWs, the output power is increased by 27% at 20 mA, and by 15% at 100 mA current injections. This improvement is mainly attributed to the enhanced efficiency of carrier injection into QWs and the improved capability of carrier transport.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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. The simulation results also suggest that the efficiency droop is markedly improved when the traditional GaN barriers are replaced by AlGaN barriers.