Performance Of Blue Light-emitting Diodes Research Articles

Size effect on optical performance of blue light-emitting diodes

In this paper, size effects on optical performance of blue light-emitting diodes (LEDs) are investigated. The essential physical mechanism is studied by fabricating LEDs with various sizes of the active area and testing optical characteristics. It is found that micro-LEDs have better light extracting efficiency and thermal dissipation compared with broad-area LEDs, which is likely due to the small ratio of perimeter and active area. Furthermore, micro-LEDs are more beneficial for displays due to the stable wavelength under the low pulse width modulation (PWM) current density.

Performance of Blue LEDs With N-AlGaN/N-GaN Superlattice as Electron-Blocking Layer

The characteristics of InGaN-based blue light-emitting diodes (LEDs) with an AlGaN/GaN superlattice (SL) electron-blocking layer (EBL) of gradual Al molar fraction below the active region are analyzed numerically. The output power, internal quantum efficiency, electrostatic fields, energy band diagrams, carrier concentrations, radiative recombination, and electron leakage current are investigated. The results indicate that the LED with n-type AlGaN/GaN SL EBL of gradual Al molar fraction has smaller electrostatic fields and lower electron leakage in its active region than the LED with a rectangular p-AlGaN EBL or n-AlGaN EBL. These result in a markedly reduced efficiency droop.

Effects of the p-AlInGaN/GaN superlattices' structure on the performance of blue LEDs

The advantages of the p-AlInGaN/GaN superlattices' (SLs) structure as an electron blocking layer (EBL) for InGaN blue light-emitting diodes (LEDs) were studied by experiment and APSYS simulation. Electroluminescence (EL) measurement results show that the LEDs with the p-AlInGaN/GaN SLs' structure EBL exhibited better optical performance compared with the conventional AlGaN EBL due to the enhancement of hole concentration and hole carrier transport efficiency, and the confinement of electrons' overflow between multiple quantum-wells (MQWs) and EBL.

Enhanced Performance of Blue Light-Emitting Diodes With InGaN/GaN Superlattice as Hole Gathering Layer

An InGaN/GaN superlattice (SL) with Mg-doped barriers was designed and inserted into the InGaN-based blue light-emitting diodes (LEDs) as a hole gathering layer (HGL) to promote hole injection into the active region. The fabricated LEDs with the SL HGL show 36.4% increase in light output power at an injection current of 200 mA. Meanwhile, the efficiency droop is also mitigated effectively, as compared to the traditional LEDs. The improved performance is attributed to increased hole injection efficiency and decreased electron leakage into the p-type region.

Effects of extreme dc-ageing and electron-beam irradiation in InGaN/AlGaN/GaN light-emitting diodes

Changes in the optical performances of blue light-emitting diodes based on InGaN/AlGaN/GaN heterostructures were studied after ageing stages consisting of electrical stress at a dc forward current of 100 mA and high-energy electron-beam irradiation. The structural modifications induced by ageing were investigated and a physical description of the nature of the damage was defined by means of complementary techniques such as electroluminescence, cathodoluminescence and current–voltage characterization at different temperatures. The onset of a broad optical band at about 3.08 eV and a consistent reduction of the quantum well optical efficiency revealed a substantial degradation of the heterostructure after ageing. The new band, ascribed to the formation of Mg-related complexes acting as shallow acceptors, occurred together with a dramatic change in the current–voltage curves. Its quenching after electron-beam irradiation and its recurrence after further electrical stress suggested the metastable nature of Mg-related complexes.

Influence of a GaN interfacial layer between n+-GaN and active layer on the characteristics of blue light-emitting diodes

Influence of a GaN interfacial layer with graded growth rate and modulated Si-doping between n+-GaN and InGaN/GaN multiquantum well on device performance of blue light-emitting diodes (LEDs) was investigated. It was found that the introduction of a GaN interfacial layer leads to an improvement of current–voltage characteristics and also an enhancement of output power compared to a conventional LED. These could result from the removal of spiral growth hillocks and smoothened morphology at the interface, as confirmed by atomic force microscopy measurements, which might cause the leakage current to decrease and the current injection into the active layer to enhance.