Jih-Yuan Chang

Advantages of blue InGaN multiple-quantum well light-emitting diodes with InGaN barriers

The advantages of blue InGaN light-emitting diodes (LEDs) with InGaN barriers are studied. The L-I curves, carrier concentrations in the quantum wells, energy band diagrams, and internal quantum efficiency are investigated. The simulation results show that the InGaN/InGaN LED has better performance over its conventional InGaN/GaN counterpart due to the enhancement of electron confinement, the reduced polarization effect between the barrier and well, and the lower potential barrier height for the holes to transport in the active region. The simulation results also suggest that the efficiency droop is markedly improved when the traditional GaN barriers are replaced by InGaN barriers.

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. The simulation results also suggest that the efficiency droop is markedly improved when the traditional GaN barriers are replaced by AlGaN barriers.

Advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers

The advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers are studied. The energy band diagrams, carrier concentrations in the quantum wells, radiative recombination rate in the active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results show that the InGaN/GaN-InGaN-GaN light-emitting diode has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams which are favorable for the injection of electrons and holes and uniform distribution of these carriers in the quantum wells.

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

Efficiency enhancement of the blue InGaN light-emitting diodes (LEDs) with InGaN-AlGaN-InGaN barriers is studied numerically. The energy band diagrams, carrier concentrations in quantum wells, radiative recombination rate in active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results suggest that the blue InGaN/InGaN-AlGaN-InGaN LED has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams, which are caused mainly by the reduced polarization charges at the interface between the well and barrier.

Simulation of blue InGaN quantum-well lasers

For InGaN laser diodes with emission wavelengths longer than 435 nm, the threshold current density usually increases with the number of InGaN well layers. This phenomenon could be attributed to the dissociation of the high indium content InGaN well layer at a high growth temperature of 750 °C due to a high InGaN dissociation pressure. In this article, the laser performance of the blue InGaN laser diode structures have been numerically investigated with a laser technology integrated program simulation program. The simulation results suggest that the inhomogeneous hole distribution in the quantum wells also plays an important role in the laser performance as a function of the number of InGaN well layers. In addition to the inhomogeneous hole distribution in the quantum wells, the phenomenon and resolution of the electronic current overflow problem in the blue InGaN quantum-well lasers are also investigated.

Numerical Study on the Influence of Piezoelectric Polarization on the Performance of p-on-n (0001)-Face GaN/InGaN p-i-n Solar Cells

The influence of piezoelectric polarization on the performance of p-on-n (0001)-face GaN/InGaN p-i-n solar cells is investigated. Simulation results show that the energy band is tilted into the direction detrimental for carrier collection due to the polarization-induced electric field. When the indium composition of InGaN layer increases, this unfavorable effect becomes more serious which, in turn, deteriorates the device performance. This discovery demonstrates that, besides the issue of crystal quality, the problem caused by the polarization effect needs to be overcome for the development of GaN-based solar cells.

Improvement in Electron Overflow of Near-Ultraviolet InGaN LEDs by Specific Design on Last Barrier

Specific designs on the last barrier of near-ultraviolet InGaN light-emitting diodes are investigated numerically in order to diminish the electron leakage current without sacrificing the injection efficiency of holes. Due to the reduction of electron leakage current, the recombination of electrons and holes in the p-layers is decreased and, thus, more holes can be injected into the active region. The simulation results show that the optical performance and internal quantum efficiency are markedly improved when the last GaN barrier near the p-layers is partially replaced by In0.01Ga0.99N layer and intentionally p-doped.

Investigation of green InGaN light-emitting diodes with asymmetric AlGaN composition-graded barriers and without an electron blocking layer

In this study, a green InGaN light-emitting diode with asymmetric AlGaN composition-graded barriers and without the use of an AlGaN electron blocking layer is presented to possess markedly enhanced optical and electrical performance. The simulation results show that the output power is increased by 10.0% and 33.2%, which corresponds to an increment of 7% and 29.4% in internal quantum efficiency, at 100 mA when the conventional GaN barriers are replaced by the asymmetric AlGaN composition-graded barriers and the commonly used AlGaN electron blocking layer is removed. The simulation results suggest that the improved device performance is due mainly to the markedly enhanced injection of holes into the active region.

Numerical analysis on the effects of bandgap energy and polarization of electron blocking layer in near-ultraviolet light-emitting diodes

The influences of bandgap energy and polarization of the electron blocking layer (EBL) in near-ultraviolet light-emitting diodes (NUV LEDs) are systematically investigated. Design curves for the output power of NUV LEDs as a function of bandgap energy and polarization of EBL are provided. The simulation results show that, when the bandgap of the EBL increases, the polarization and polarization-induced charge increase accordingly. Both mechanisms have opposite effects for the EBL in confining electrons. The NUV LEDs with an EBL of large bandgap or small polarization have improved performance due to the enhanced efficiency of electron confining and hole injection.