Coincidence measurements of secondary ions and scattered ions in collision between slow Ar 6+ and a GaN(0001) surface (original) (raw)
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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.
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.
Ion Sputter Induced Interfacial Reaction in Prototypical Metal-GaN System
Scientific reports, 2018
Contact property is now becoming to be a key factor for achieving high performance and high reliability in GaN-based III-V semiconductor devices. Energetic ion sputter, as an effective interface probe, is widely used to profile the metal/GaN contacts for interfacial analysis and process optimization. However, the details of ion-induced interfacial reaction, as well as the formation of sputter by-products at the interfaces are still unclear. Here by combining state-of-the-art Ar ion sputter with in-situ X-ray photoelectron spectroscopy (XPS) and ex-situ high resolution transmission electron microscopy (HRTEM), we have observed clearly not only the ion-induced chemical state changes at interface, but also the by-products at the prototypical Ti/GaN system. For the first time, we identified the formation of a metallic Ga layer at the GaO/GaN interface. At the Ti/GaO interface, TiC components were also detected due to the reaction between metal Ti and surface-adsorbed C species. Our stud...
Electron emission from the interaction of multiply charged ions with a Au(110) surface
Surface Science, 1986
We have measured energy distributions of electrons produced during slow glancing collisions of H-like and He-like N and O projectiles with a clean Au(llO) surface. For the case of the H-like incident projectiles, two peaks, at 250 and 350 eV, and 250 and 490 eV for incident N +6 and O +7 , respectively, are observed. Both peaks are associated with Auger transitions to the K-shell vacancy brought into the collision by the incident H-like multicharged ions: from the higher lying shells of the projectile in the case of the high energy peaks, and from the target inner shells in the case of the low energy peaks.
Molecular effect on surface topography of GaN bombarded with PF 4 ions
We study surface topography and thickness of GaN layers implanted at room temperature with 1.3 keV/amu F, P, and PF 4 cluster ions. Results show that the density of collision cascades has a dramatic effect on the surface roughness and the thickness of implanted layers. Surface roughness increases with increasing cascade density. For very dense cascades produced by PF 4 ions, the evolution of layer thickness is dominated by ion-induced sputtering. In contrast, for the case of P ions producing less dense cascades, ion-induced swelling is observed.
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.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
Experimental and simulated energy distributions of Ga þ and In þ secondary ions produced by 4 keV Ne þ , Ar þ and Kr þ bombardment of the A III B V semiconductors (GaP, GaAs, GaSb, InP, InAs and InSb) are reported. The measurements were carried out for a wide range of initial energy (up to 1000 eV) in a small solid angle along the surface normal, without applying electric field to extract the ions into the mass-energy analyser. It is shown that the energy spectra are complex, with evident high-energy hump, whose relative intensity increases with the mass of the second component (P, As, Sb) of the compound. The Sigmund-Thompson distribution cannot fit reliably these data, and a satisfactory approximation of the measured spectra was obtained with a sum of two decaying exponential functions to describe the contribution of both, the isotropic linear collision cascades and the outward knock-on atoms. The experimental results are compared with simulations based on the MARLOWE computer code.
Dissociation of GaN2+ and AlN2+ in APT: Analysis of experimental measurements
The Journal of Chemical Physics, 2018
The use of a tip-shaped sample for the atom probe tomography technique offers the unique opportunity to analyze the dynamics of molecular ions in strong DC fields. We investigate here the stability of AlN2+ and GaN2+ dications emitted from an Al0.25Ga0.75N sample in a joint theoretical and experimental study. Despite the strong chemical resemblance of these two molecules, we observe only stable AlN2+, while GaN2+ can only be observed as a transient species. We simulate the emission dynamics of these ions on field-perturbed potential energy surfaces obtained from quantum chemical calculations. We show that the dissociation is governed by two independent processes. For all bound states, a mechanical dissociation is induced by the distortion of the potential energy surface in the close vicinity of the emitting tip. In the specific case of GaN2+, the relatively small electric dipole of the dication in its ground 13Σ− and excited 11Δ states induces a weak coupling with the electric field...
GaN evaporation and enhanced diffusion of Ar during high-temperature ion implantation
Journal of Applied Physics, 2003
GaN films were implanted with 150 keV Ar ϩ at temperatures up to 1100°C to a dose of 3 ϫ10 15 cm Ϫ2 . Concentration profiles of Ar were measured by secondary ion mass spectroscopy and depth distributions of ion-induced damage were estimated from Rutherford backscattering/ channeling spectra. No redistribution of Ar atoms was detected up to 700°C. At 1000°C a deep penetrating diffusion tail and a shift of the Ar peak to the surface were observed. At temperatures higher than 800°C shift of the damage peak to the surface was also observed. We attributed the shift of the Ar peak and the damage peaks to evaporation of thin layer of GaN during high-temperature implantation and estimated its temperature dependence.