Miao-Chan Tsai

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.

Effect of P-Type Last Barrier on Efficiency Droop of Blue InGaN Light-Emitting Diodes

P-type doping in the last barrier is proposed to improve the efficiency droop of the blue InGaN light-emitting diodes (LEDs). The light-current curves, energy band diagrams, carrier concentrations, radiative recombination efficiency, and internal quantum efficiency of the blue LEDs under study are investigated. The simulation results show that the efficiency droop is significantly improved when the last undoped GaN barrier in a typical blue LED is replaced by a p-type GaN barrier. The simulation results suggest that the improvement in efficiency droop is mainly due to the decrease of electron current leakage and increase of hole injection efficiency.

Improvement in output power of a 460 nm InGaN light-emitting diode using staggered quantum well

Staggered quantum well structures are studied to eliminate the influence of polarization-induced electrostatic field upon the optical performance of blue InGaN light-emitting diodes (LEDs). Blue InGaN LEDs with various staggered quantum wells which vary in their indium compositions and quantum well width are theoretically studied and compared by using the APSYS simulation program. According to the simulation results, the best optical characteristic is obtained when the staggered quantum well is designed as In0.20Ga0.80N (1.4 nm)–In0.26Ga0.74N (1.6 nm) for blue LEDs. Superiority of this novelty design is on the strength of its enhanced overlap of electron and hole wave functions, uniform distribution of holes, and suppressed electron leakage in the LED device.

Effect of N-Type AlGaN Layer on Carrier Transportation and Efficiency Droop of Blue InGaN Light-Emitting Diodes

The effect of an n-type AlGaN layer on the physical properties of blue InGaN light-emitting diodes (LEDs) is investigated numerically. The p-type AlGaN electron-blocking layer is usually used in blue LEDs to reduce the electron leakage current. However, the p-type AlGaN layer also retards the injection of holes, which leads to the degradation of efficiency at high current. To improve the efficiency droop of blue InGaN LEDs at high current, an n-type AlGaN layer below the active region is proposed to replace the traditional p-type AlGaN layer. The simulation results show that the improvement in efficiency droop is due mainly to the sufficiently reduced electron leakage current and more uniform distribution of holes in the quantum wells.

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.

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.

Numerical Study of Blue InGaN Light-Emitting Diodes With Varied Barrier Thicknesses

This letter demonstrates the outcomes of numerical investigation of the InGaN light-emitting diodes with varied barrier thicknesses. Compared with the original structure with equal barrier thickness, the analyses focus on hole injection efficiency, carrier distribution, electron leakage, and radiative recombination. Simulation approach yields to a result that, when varied barrier thicknesses are used, more than one quantum well contributes to radiative recombination at high injection current which leads to the improvement of efficiency droop. Further analysis indicates that the thinner barrier located close to the p-side layers is beneficial for increasing hole injection, which leads to the reduction of electron leakage; moreover, holes can be confined in more quantum wells in such condition as well.

Enhancement of Light Power for Blue InGaN LEDs by Using Low-Indium-Content InGaN Barriers

The optical properties of blue InGaN LEDs that emit in a spectral range from 410 to 445 nm are theoretically investigated by using the APSYS simulation program. It is found that the light performance can be enhanced effectively when the conventional GaN barrier layers are replaced by In_0.02Ga_0.98N and In_0.05Ga_0.95N barrier layers. The numerical results indicate that the output power of LEDs with In_0.02Ga_0.98 N barrier layers is improved gradually above the emission wavelength of 410 nm. However, when the In_0.05Ga_0.95N barrier layers are used, the emitting power of LEDs varies significantly when the emission wavelength changes. When the emission wavelength is 410 nm, the use of GaN and In_0.02Ga_0.98N barrier layers can lead to higher output power. However, if the emission wavelength is 445 nm, the use of In_0.05Ga_0.95N barrier layers is beneficial for maintaining high output power.