Defect clustering in irradiation of GaN by single and molecular ions (original) (raw)
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Effects of defect clustering on optical properties of GaN by single and molecular ion irradiation
Journal of Applied Physics, 2013
The effects of irradiation by F, P and PF 4 on optical properties of GaN were studied experimentally and by atomistic simulations. Additionally, the effect of Ag was studied by simulation. The irradiation energy was 0.6 keV/amu for all projectiles. The measured photoluminescence (PL) decay time was found to be decreasing faster when irradiation was done by molecular ion compared to light ion irradiation. The PL decay time change is connected with the types of defect produced by different projectiles. Simulation results show that light ions mainly produce isolated point defects while molecular and heavy ions produce clusters of points defects. The total amount of defects produced by the PF 4 projectile was found to be very close to the sum of all defects produced in five individual cascades started by one P and four F single ions. This and the similar depth profiles of damage produced by molecular and light ion irradiation suggest that defect clusters are one of the important reasons for fast PL decay. Moreover, the simulations of irradiation by Ag ions, whose mass is close to the mass of the PF 4 molecule, showed that the produced defects are clustering in even bigger conglomerates compared to PF 4 case. The latter has a tendency to split in the pre-surface region, reducing on average the density of the collision cascade.
Journal of Physics D: Applied Physics, 2017
An investigation of mechanisms of enhancement of irradiation-induced damage formation in GaN under molecular in comparison to monatomic ion bombardment is presented. Ionimplantation-induced effects in wurtzite GaN bombarded with 0.6 keV/amu F, P, PF2, and PF4 ions at room temperature are studied experimentally and by cumulative MD simulation in the correct irradiation conditions. In the low dose regime, damage formation is correlated with a reduction in photoluminescence decay time, whereas in the high dose regime, it is associated with the thickness of the amorphous layer formed at the sample surface. In all the cases studied, a switch to molecular ion irradiation from bombardment by its monatomic constituents enhances the damage accumulation rate. Implantation of heavy Ag ion, having approximately the same mass as the PF4 molecule, is less effective in surface damage formation, but leads to noticeably higher damage accumulation in the bulk.. The cumulative MD simulations do not reveal any significant difference in the total amount of both point defects and small defect clusters produced by light monatomic and molecular ions. On the other hand, increased production of large defect clusters by molecular PF4 ions is clearly seen in the vicinity of the surface. Ag ions produce almost the same number of small, but more large defect clusters compare to the others. This findings show that the enhancement of stable damage formation in GaN under molecular, as well as under heavy monatomic ion irradiation, can be related to the higher formation probabilityof large defect clusters.
Atomistic simulation of damage production by atomic and molecular ion irradiation in GaN
Journal of Applied Physics, 2012
Gallium nitride (GaN) has emerged as one of the most important semiconductors in modern technology. GaN-based device technology was mainly pushed forward by invention of p-type doping and the successful fabrication of light emitting diodes (LEDs) and laser diodes (LDs). Intensive studies in the last 20 years on GaN have significantly advanced the understanding of the properties and have expanded the range of practical applications. Beside basic lighting, current applications of GaN include high-power and high temperature electronics, microwave, optoelectronic devices, and so on. The successful production of optical devices demands efficient tuning of charge carrier lifetime where defect engineering plays a vital role. During growth, varying the level of recombination centers is difficult, whereas ion irradiation can do this job efficiently on a final product. On the other hand, during doping, undesirable defects can also be produced and epitaxial GaN is known to have a highly defective structure. Thus, having both positive and negative aspects, it is very important to have a detailed understanding of irradiation-induced defects. To explain experimental findings, atomic level understanding is necessary, but it is not always possible to have an atomistic view of defect dynamics in experiments. Some damage build-up studies by single ions have been reported in the literature, but not many by molecular ions. In this thesis, the irradiation of GaN by single and molecular ions by the means of atomistic simulations was studied. Detailed analysis mainly of what kind of defects, their distribution, reason of defect formation and time evolution have been studied and compared with experiments.
A novel Photoluminescence (PL) model for the effect of 1 MeV electron irradiation on AlGaN_GaN.pdf
A novel Photoluminescence (PL) model for the effect of 1 MeV electron irradiation on AlGaN/GaN with a variation in Si3N4 passivation layer thickness has been developed by examining the transitions and changes in defect populations and energy levels. The PL results of SixN/AlGaN/GaN gives information on the spatial localization of impurities such as oxygen and silicon, which are precursors to the D 0 X centers, deeper impurities like magnesium, and Vn and VGa donor information. The Si3N4 passivation layer shows a mono-atomic variation with PL intensity prior to 1MeV radiation. The post radiation Pl gives a 50nm peak and a 20 nm minimum in the deep center range, but then reverses to mono-atomic variation in the near band edge range. There is a shift in the main D 0 X center in the rear band edge due to mismatch lattice constants which results from tensile strain. The model that follows seeks to explain the observed changes in the PL due to 1 MeV electron irradiation. The changes with Si3N4 thickness pre-irradiation are explained as due to the attenuation of the PL laser beam going through the material, and corresponded linearly to the thickness of the Si3N4 pre-irradiation, but not post irradiation.
Molecular dynamics study of defect formation in GaN cascades
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
Simulations of irradiation effects in compound semiconductors require interatomic potentials which describe not only the compound phases, but also the pure constituents and defects. We discuss a systematic approach based on the analytic bond-order scheme for constructing such potentials and give an example for GaN. Finally, this potential is employed for simulations of defect formation in GaN by ion irradiation for recoils in the 200 eV to 10 keV energy range. Results on the total damage production are presented and compared with other semiconductors and experiments.
Photoluminescence and Excitation Spectra of Deep Defects in GaN
MRS Proceedings, 2001
ABSTRACTDeep defects responsible for broad bands in the red-to-green range of the photoluminescence (PL) spectrum of undoped and Si-doped GaN grown by molecular beam epitaxy (MBE) and hydride vapor phase epitaxy (HVPE) were studied by employing PL and PL excitation (PLE) methods. In HVPE grown samples, a red luminescence (RL) and a green luminescence (GL) bands were observed, respectively, at about 1.9 and 2.4 eV. Similar in positions but different in properties red and green bands (RL2 and GL2, respectively) dominated in the samples grown in Ga-rich conditions by MBE with radio frequency plasma as a nitrogen source (RF-MBE). A yellow luminescence (YL) with a maximum at about 2.2 eV dominated in the samples with ammonia used as a nitrogen source (NH3-MBE). It has been established from the variation of temperature, excitation intensity and excitation wavelength that the abovementioned five bands are related to different deep-level defects.
Direct evidence of N aggregation and diffusion in Au[sup +] irradiated GaN
Applied Physics Letters, 2006
A surface amorphized layer and a buried disordered structure were created in gallium nitride ͑GaN͒ irradiated using 1.0 MeV Au + ions to fluences of 25 and 70 Au + /nm 2 at room temperature. Bubbles of N 2 gas within both the amorphized and disordered GaN are formed. A gradient profile with a lower N concentration in the amorphized region is observed, which provides direct evidence of N loss by diffusion in the Au + irradiated GaN. These results are important to understanding the amorphization processes in GaN and may have significant implications for the design and fabrication of GaN-based devices.
Physical Review B, 2010
We present a detailed study of the thermal evolution of H ion-induced vacancy related complexes and voids in bulk GaN implanted under ion-cut conditions. By using transmission electron microscopy, we found that the damage band in as-implanted GaN is decorated with a high density of nanobubbles of ϳ1 -2 nm in diameter. Variable energy Doppler broadening spectroscopy showed that this band contains vacancy clusters and voids. In addition to vacancy clusters, the presence of V Ga , V Ga -H 2 , and V Ga V N complexes was evidenced by pulsed low-energy positron lifetime spectroscopy. Subtle changes upon annealing in these vacancy complexes were also investigated. As a general trend, a growth in open-volume defects is detected in parallel to an increase in both size and density of nanobubbles. The observed vacancy complexes appear to be stable during annealing. However, for temperatures above 450°C, unusually large lifetimes were measured. These lifetimes are attributed to the formation of positronium in GaN. Since the formation of positronium is not possible in a dense semiconductor, our finding demonstrates the presence of sufficiently large open-volume defects in this temperature range. Based on the Tao-Eldrup model, the average lattice opening during thermal annealing was quantified. We found that a void diameter of 0.4 nm is induced by annealing at 600°C. The role of these complexes in the subsurface microcracking is discussed.
Optical properties of electron-irradiated GaN
MRS Internet Journal of Nitride Semiconductor Research, 1998
The electronic structure of defects produced by 2.5-MeV electron irradiation and their effect on optical properties of GaN are investigated using photoluminescence (PL) and optically detected magnetic resonance (ODMR) techniques. The electron irradiation is shown to produce, in particular, a deep PL band with a no-phonon line at around 0.88 eV followed by a phonon-assisted sideband. We suggest that this emission is caused by an internal transition between excited and ground state of a deep defect. The excited state is a multiple-level state, as revealed from temperature dependent PL and level anti-crossing experiments. The electronic structure of the 0.88 eV defect is shown to be sensitive to the internal strain in the GaN epilayers. The ODMR studies reveal that the principal axis of the defect coincides with the c-axis of the host lattice and should therefore be either an on-site point defect or an axial complex defect along the c-axis.