Yun-Yan Zhang

Performance enhancement of blue light-emitting diodes with a special designed AlGaN/GaN superlattice electron-blocking layer

The characteristics of the nitride-based blue light-emitting diode (LED) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al mole fraction are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells, energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with an AlGaN/GaN SL EBL of gradual Al mole fraction has a better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in its active region over the LED with a conventional rectangular AlGaN EBL or with a normal AlGaN/GaN SL EBL. The results also show that the efficiency droop is markedly improved when the SL EBL of gradual Al mole fraction is used.

Performance enhancement of blue light-emitting diodes with AlGaN barriers and a special designed electron-blocking layer

In this study, the characteristics of the nitride-based blue light-emitting diode (LED) with AlGaN barriers are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells (QWs), energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with AlGaN barriers has a better hole-injection efficiency and an enhanced carrier confinement in its active region over the conventional counterpart with GaN barriers. The results also show that the AlGaN electron-blocking layer (EBL) with a gradual variation of Al mole fraction has a significantly enhanced electron blocking capability as well as a greatly improved hole-injection efficiency. When Al0.08Ga0.92N QW barriers and the special designed EBL are used, the electroluminescence emission intensity is increased greatly by 69% at 200 A/cm2 and the efficiency droop is reduced markedly to 8.7% from 85% at 400 A/cm2 compared with those of the conventional LED.

Performance enhancement of blue light-emitting diodes without an electron-blocking layer by using special designed p-type doped InGaN barriers

In this study, the characteristics of the nitride-based blue light-emitting diode (LED) without an electron-blocking layer (EBL) are analyzed numerically. The emission spectra, carrier concentrations in the quantum wells (QWs), energy band diagrams, electrostatic fields, and internal quantum efficiency (IQE) are investigated. The simulation results indicate that the LED without an EBL has a better hole-injection efficiency and smaller electrostatic fields in its active region over the conventional LED with an AlGaN EBL. The simulation results also show that the LED without an EBL has severe efficiency droop. However, when the special designed p-type doped InGaN QW barriers are used, the efficiency droop is markedly improved and the electroluminescence (EL) emission intensity is greatly enhanced which is due to the improvement of the hole uniformity in the active region and small electron leakage.

Improvement of Efficiency Droop in Blue InGaN Light-Emitting Diodes With p-InGaN/GaN Superlattice Last Quantum Barrier

The blue InGaN light-emitting diodes (LEDs) with specific designs of p-InGaN/GaN superlattice (SL) last quantum barrier are investigated numerically and experimentally. The proposed SL with a graded indium mole fraction from 0% to 5% shows improved efficiency droop and superior optical characteristics in comparison with the conventional LEDs. As indicated by the simulation results, the promotion of hole injection and the reduction of electron leakage play important roles in these improvements. Fabricated LEDs with this specific design exhibit stronger emission intensity, smaller forward voltage, and larger light output power compared to its counterparts.

Performance Enhancement of Near-UV Light-Emitting Diodes With an InAlN/GaN Superlattice Electron-Blocking Layer

In this study, the characteristics of the nitride-based near-UV light-emitting diode (LED) with an InAlN/GaN superlattice (SL) electron-blocking layer (EBL) are analyzed numerically and experimentally. The emission spectra, carrier concentrations in the quantum wells, energy-band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The results indicate that the LED with an InAlN/GaN SL EBL has a better hole-injection efficiency and lower electron leakage over the LED with a conventional rectangular AlGaN EBL or with an AlGaN/GaN SL EBL. The results also show that the efficiency droop is markedly improved when the InAlN/GaN SL EBL is used.

Performance Enhancement of Blue Light-Emitting Diodes Without an Electron-Blocking Layer by Using p-Type Doped Barriers and a Hole-Blocking Layer of Low Al Mole Fraction

In this paper, the characteristics of the nitride-based blue light-emitting diode (LED) without an electron-blocking layer (EBL) are analyzed numerically. The emission spectra, carrier concentrations in the quantum wells (QWs), energy band diagrams, electrostatic fields, and internal quantum efficiency are investigated. The simulation results indicate that the LED without an EBL has a better hole-injection efficiency and smaller electrostatic fields in its active region over the conventional LED with an AlGaN EBL. The simulation results also show that the LED without an EBL has severe efficiency droop. However, when the p-type doped QW barriers and a hole-blocking layer are used, the efficiency droop is markedly improved and the electroluminescence emission intensity is greatly enhanced.

Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers

The performance of InGaN blue light-emitting diodes (LEDs) with different kinds of electron-blocking layers is investigated numerically. We compare the simulated emission spectra, electron and hole concentrations, energy band diagrams, electrostatic fields, and internal quantum efficiencies of the LEDs. The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer (EBL) has a strong spectrum intensity, mitigates efficiency droop, and possesses higher output power compared with the LEDs with the other three types of EBLs. These advantages could be because of the lower electron leakage current and more effective hole injection. The optical performance of the specifically designed LED is also improved in the case of large injection current.

Correction to “Performance Enhancement of Blue Light-Emitting Diodes Without an Electron-Blocking Layer by Using p-Type Doped Barriers and a Hole-Blocking Layer of Low Al Mole Fraction” [Feb 12 169-174]

In the above titled paper (ibid., vol.48, no. 2, pp. 169-174, Feb. 2012), the affiliation of Yun-Yan Zhang should have read as follows. Y.Y. Zhang is with the Institute of Optoelectronic Materials and Technology, South China Normal University, Guangzhou 510631, China (e-mail: yunyan_zhang@126.com).