Low-energy Electron-beam Irradiation Treatment Research Articles

Microcathodoluminescence spectra evolution for planar and nanopillar multiquantum-well GaN-based structures as a function of electron irradiation dose

Effects of low energy electron beam irradiation (LEEBI) of planar and nanopillar InGaN/GaN multiquantum well light emitting diode structures are discussed. The bands observed in microcathodoluminescence (MCL) spectra were attributed to recombination involving two types of InGaN quantum dots with lower (2.92 eV MCL band) and higher (2.75 eV) indium concentration. During the LEEBI treatment, the intensity of both MCL lines first decreased, presumably due to the introduction of radiation defects, then, after the dose of 0.2 C/cm2 increased, reached a maximum and then again decreased. At the same time, the peak energy showed a red shift at low irradiation doses and a blue shift at high doses. The results are explained by an interplay between the increasing density of nonradiative recombination defects and quantum dots during irradiation. The difference between the nanopillar and planar structures is attributed to a stronger impact of surface defects in nanopillars.

A method to improve the light emission efficiency of Mg-doped GaN

Scanning cathodoluminescence (CL) spectroscopy and imaging were used to study the effect of post-growth processing on the CL efficiency of metal–organic vapour phase epitaxy-grown Mg-doped GaN. In this work, two treatments, thermal annealing in high-purity gaseous atmospheres (N2, O2 and H2(5%)/N2) and low-energy electron beam irradiation (LEEBI), have been investigated. Post-growth annealing in a H2/N2 atmosphere followed by LEEBI leads to a significant enhancement of the free electron-to-bound Mg-acceptor (e, Mg) CL emission and a reduction of nonradiative centres involving native defects. The presented results demonstrate that the combination of post-growth annealing in a H2/N2 atmosphere and LEEBI dissociation of Mg–H complex acceptors significantly improves the light emitting efficiency of Mg-doped p-type GaN. Conversely, the samples annealed in a N2 or O2 atmosphere exhibit a reduced (e, Mg) emission after both annealing and LEEBI treatment.

Low-energy electron-beam irradiation and yellow luminescence in activated Mg-doped GaN

The effect of low-energy electron-beam irradiation (LEEBI) on native defects and residual impurities in metalorganic-vapor-phase-epitaxy-grown, lightly Mg-doped, p-type GaN was studied by temperature-resolved and excitation power density-resolved cathodoluminescence spectroscopy. Following the LEEBI treatment, the ubiquitous shallow donor–acceptor-pair emission at 3.27 eV decreased, while a deeper DAP emission at ∼3.1 eV dramatically increased in intensity, and a broad yellow luminescence band centered at 2.2 eV evolved. The results clearly indicate that the centers involved in the 3.27 eV transition are not stable during irradiation by low-energy electrons. Further, we report that the LEEBI-treatment not only dissociates neutral Mg-H complexes as intended, but simultaneously dissociates other hydrogenated defect complexes, giving rise to additional radiative recombination channels.

Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN

The effect of low-energy electron beam irradiation (LEEBI) on residual hydrogen impurities and native defects in activated metalorganic vapor phase epitaxy-grown Mg-doped (p-type) GaN layers was studied by cathodoluminescence (CL) microanalysis and spectroscopy at temperatures between 80 and 300 K. The LEEBI treatment dissociates (Mg–H)0 complexes producing (i) at 300 K, a significant increase in a free-to-bound transition (e,Mg0) centered at 3.26 eV and (ii) at 80 K, a substantial decrease in a H–Mg donor–acceptor pair emission at 3.27 eV. In-plane and depth-resolved CL imaging reveals a direct correlation between the spatial distribution of the injected carriers and the depth and lateral distribution of activated Mg acceptors. This finding strongly suggests that hydrogen dissociation results from electron-hole recombination at hydrogen defect complexes rather than heating by the electron beam. The results at 80 K indicate that the process of dissociation of hydrogen from (Mg–H)0 complexes is accompanied by a generation of additional defect centers. It is proposed that following LEEBI hydrogen does not leave the specimen, but instead associates with nitrogen vacancies, generating additional recombination channels.

Direct Patterning of the Current Confinement Structure for p-Type Column-III Nitrides by Low-Energy Electron Beam Irradiation Treatment

Partial low-energy electron beam irradiation (LEEBI) treatment was used to fabricate UV/blue light-emitting devices based on column-III nitrides having a directly patterned current confinement structure. The newly developed devices show very low leakage reverse current, stable operation at high pulsed current injection, and strong and narrow violet emission at room temperature.

Conductivity control of GaN and fabrication of UV/blue GaN light emitting devices

The development of the technology for heteroepitaxial growth of high-crystalline-quality GaN films on sapphire substrates using AlN buffer layers, the establishment of a technique for control of conductivity for n-type GaN by Si-doping, and the realization of p-type Mg-doped GaN using low-energy electron-beam irradiation treatment have enabled us to fabricate a high performance, short wavelength LED based on GaN. In this paper, we review the recent developments of AlGaN/GaN multi-layered structures showing quantum-size effects, and of LEDs with AlGaN/GaN double heterostructures which emit light in the blue to UV region with output power of more than a few milliwatts at room temperature.