Collision cascade density is one of the most important parameters that determine radiation damage accumulation in semiconductors under ion bombardment. We perform calculation of collision cascade parameters formed in β-Ga2O3 by irradiation with 1.3 keV/amu atomic F, P, and molecular PF4 ions using two different methods: the method considering sub-cascade formation, and by calculation an average number of vacancies in spheres of fixed radius. The calculated results are compared with experimental data on damage accumulation in β-Ga2O3 under irradiation with aforementioned ions. It is shown that both methods qualitatively predict the effect of collision cascade density on radiation damage accumulation in gallium oxide. Fractal nature of cascades formed in β-Ga2O3 is established, corresponding fractal dimension is calculated.

In the paper, the distributions of structure damage created in alpha-phase of gallium oxide by keV fluorine, phosphorus and xenon ion irradiation, have been obtained at room temperature. A noticeable effect of the average individual collision cascade density on the stable damage production efficiency at the surface was established. In contrast to many other semiconductors, an intermediate damage peak appeared in the alpha-Ga2O3 between the surface and bulk maxima. This intermediate peak visible in the RBS/C spectra at low damage levels was discovered for the first time. Characteristic peculiarities of the discovered maximum were investigated.

We study radiation damage accumulation in alpha polymorph of gallium oxide (α-Ga2O3) epitaxial layers under irradiation with 40 keV monatomic P and 140 keV molecular PF4 ions. The distribution of stable structural damage is bimodal in both cases. The growth rate of the surface disordered layer under PF4 ion irradiation is significantly higher than that under monatomic P ion bombardment. At the same time, monatomic ion irradiation is more efficient in the bulk defect peak formation. Thus, the density of displacement cascades strongly affects the formation of stable damage in α-gallium oxide. The doses required to create the same level of disorder in the metastable α-polymorph are higher than that in the thermodynamically stable α-. Mechanisms of damage formation in these polymorphs are different. Keywords: gallium oxide, α-Ga2O3, ion bombardment, collision cascades, radiation damage, collision cascade density, defect engineering, radiation resistance.

We study radiation damage accumulation in alphapolymorph of gallium oxide (α-Ga2O3) epitaxial layers under irradiation with 40 keV monatomic P and 140 keV molecular PF4 ions. The distribution of stable structural damage is bimodal in both cases. The growth rate of the surface disordered layer under PF4 ion irradiation is significantly higher than that under monatomic P ion bombardment. At the same time, monatomic ion irradiation is more efficient in the bulk defect peak formation. Thus, the density of displacement cascades strongly affects the formation of stable damage in α-gallium oxide. The doses required to create the same level of disorder in the metastable α-polymorph are higher than that in the thermodynamically stable β-Ga2O3. Mechanisms of damage formation in these polymorphs are different.

The mechanisms of ion-induced defect formation and physical characteristics promoting radiation tolerance of wide and ultra-wide bandgap semiconductors are not well-studied and understood. In contrast to gallium nitride (GaN), gallium oxide (Ga2O3) can be crystallized in several polymorphs having different crystal structures and physical properties. In the preset paper, the damage buildup in wurtzite GaN as well as in corundum (alpha-) and monoclinic (beta-) Ga2O3 polymorphs bombarded at room temperature with 40 keV P+ ions is studied by Rutherford backscattering/channeling spectrometry. We demonstrate that ion-beam-induced damage formation in Ga2O3 is different from that observed in GaN and dramatically depends on the polymorph type. Both Ga2O3 polymorphs cannot be rendered amorphous and exhibit considerably higher damage saturation at similar to 90% of the full amorphization as compared to that of GaN. Intriguing enough the metastable alpha-Ga2O3 demonstrates considerably higher radiation resistance as compared to the most thermodynamically stable beta-Ga2O3 polymorph. Furthermore, our results indicate that the sample surface and dynamic annealing play a significant role in the ion-induced damage formation processes in all Ga-based compounds studied.

The formation of nanoparticles under the irradiation of a thin metallic gold film by accelerated atomic and molecular ions is demonstrated. The obtained structures are used to form porous silicon by the metal-assisted chemical etching. The size of the gold nanoparticles and structure of porous silicon greatly depend on the type of incident particles and their fluence. A local increase in the density of energy released at the target surface under molecular ion bombardment significantly reduces the doses required to form the desired film morphologies and spread of nanoparticles over the surface and simultaneously makes a weaker radiative impact on the substrate. The shape of the fluorescence and fluorescence-excitation spectra of porous silicon obtained from the irradiated structures is independent of the irradiation parameters, but changes with the etching-solution concentration.

Silicon light-emitting diodes with luminescence associated with (113) defects have been fabricated using implantation of 350 keV oxygen ions at the dose of 3.7∙1014 cm-2 and subsequent annealing at 700ᵒC for 1 h in a chlorine-containing atmosphere. Electroluminescence was studied in wide ranges of temperature and an excitation power. The line associated with (113) defects dominates in all the spectra. The temperature dependence of the line intensity depends on the excitation power in the range of low temperatures: an increase of the intensity with activation energy of 25 meV is observed at low current density and, with the increasing current density, a rise of the intensity is not observed. At higher temperatures, a decrease of the intensity with activation energy of 59 meV occurs regardless of a current density. With the increasing temperature, the peak of the line shifts by the same energy as the forbidden gap width, while the half width of the line grows linearly.

Silicon light-emitting diodes with luminescence associated with (113) defects are fabricated by the implantation of 350-keV oxygen ions at a dose of 3 . 7 × 10 14 cm –2 and subsequent annealing at 700°C for 1 h in a chlorine-containing atmosphere. The electroluminescence is studied in wide temperature and excitation-power ranges. The line associated with the (113) defects is dominant in all the spectra. The temperature dependence of the line intensity depends on the excitation power at low temperatures: an increase in the intensity with an activation energy of 25 meV is observed at low current densities and no rise in the intensity is observed with increasing current density. At higher temperatures, an intensity with an activation energy of 59 meV is quenched irrespective of the current density. With increasing temperature, the peak of the line of the (113) defect shifts by the same energy as the energy-gap width, whereas the half width of the line grows linearly.

Formation of metal nanoparticles on silicon substrate by thin gold film irradiation with accelerated atomic and molecular ions is shown. Structures obtained were etched by metal-assisted catalytic chemical technique to get porous silicon structure. Size of gold nanoparticles and the structure of porous siliconstrongly depend on kind of incident species and ion dose. A local increase in the energy release density at the target surface that takes place during molecular ion bombardment significantly reduce the doses required for the formation of predetermined film morphology and the distribution of nanoparticles on the surface, while at the same time molecules exhibit lower radiation effect on the substrate. Luminescent properties of porous silicon do not depend on the kind of ion used, and can be tuned by composition of an etching solution

Optical effects induced in silicon-doped wurtzite (0001) GaN epilayers by keV monatomic and molecular ion irradiation were experimentally investigated. Results were analyzed together with data on structure defect formation. In all the cases under consideration, an increase in the collision cascade density (the cases of molecular and heavy atomic ion bombardment) enhances the stable damage accumulation rate and, accordingly, intensifies quenching of luminescence. The processes of PL suppression were theoretically considered as an increase of surface recombination rate of nonequilibrium photo-excited charge carriers due to production of stable damage at the irradiated subsurface layer. It is shown that carrier diffusion determines PL decay time shortening in the shallow implantation cases studied.

The concentration profiles of defects produced in structures upon the implantation of nitrogen ions into GaAs epitaxial layers with an uncovered surface and that covered with an AlN film and subsequent annealing are studied. The ion energies and the implantation doses are chosen so that the nitrogen-atom concentration profiles coincided in structures of both types. Rutherford proton backscattering spectra are measured in the random and channeling modes, and the concentration profiles of point defects formed are calculated for the samples under study. It is found that the implantation of nitrogen ions introduces nearly the same number of point defects into structures of both types, and the formation of an AlN film by ion-plasma sputtering is accompanied by the formation of an additional number of defects. However, the annealing of structures of both types leads to nearly the same concentrations of residual defects.

AbstractThe concentration profiles of defects produced in structures upon the implantation of nitrogen ions into GaAs epitaxial layers with an uncovered surface and that covered with an AlN film and subsequent annealing are studied. The ion energies and the implantation doses are chosen so that the nitrogen-atom concentration profiles coincided in structures of both types. Rutherford proton backscattering spectra are measured in the random and channeling modes, and the concentration profiles of point defects formed are calculated for the samples under study. It is found that the implantation of nitrogen ions introduces nearly the same number of point defects into structures of both types, and the formation of an AlN film by ion-plasma sputtering is accompanied by the formation of an additional number of defects. However, the annealing of structures of both types leads to nearly the same concentrations of residual defects.

The accumulation of structural damage in GaN under irradiation with accelerated F and Ne ions with energies of 1.3 and 3.2 keV/amu is investigated. It is shown that chemical effects during implantation of fluorine ions within the doses under consideration do not noticeably affect the formation of stable structural damage both in the bulk and on the surface of GaN.

Structural damage buildup in GaN under irradiation by 1.3 and 3.2 keV/amu F and Ne ions has been studied. It is shown that chemical effects during irradiation with fluorine ions do not enhance formation of stable structural damage on the surface or in the bulk of GaN at all the doses considered.

We present the results of investigation of radiation damage accumulation in GaN during its sequential co-implantation with fluorine ions of two different energies. This process is proved to be a non-commutative one, i.e. a clear difference in the amount of resulting damage is found, that depends on the sequence of the energy of bombarding ions used. Possible mechanism of the effect revealed is proposed and discussed. This mechanism also explains well experimentally established saturation of the bulk defect peak height in gallium nitride at a level remarkably below the full amorphization.

AbstractStructural defects formed in epitaxial GaAs layers as a result of 250-keV N^+ ion implantation to doses within 5 × 10^14–5 × 10^16 cm^–2 have been studied by the X-ray diffraction (XRD) and transmission electron microscopy techniques. No amorphization of the ion-implanted layer took place in the entire dose range studied. The implantation to doses of 5 × 10^14 and 5 × 10^15 cm^–2 led to the appearance of an additional peak on XRD curves, which was related to the formation of a stressed GaAs layer with positive deformation arising due to the formation of point-defect clusters. The implantation to a dose of 5 × 10^16 cm^–2 led to the formation of a dense structure of extended defects in the implanted layer, which was accompanied by the relaxation of macrostresses to the initial state.

Structural defects formed in epitaxial GaAs layers as a result of 250-keV N+ ion implantation to doses within 5 × 1014–5 × 1016 cm–2 have been studied by the X-ray diffraction (XRD) and transmission electron microscopy techniques. No amorphization of the ion-implanted layer took place in the entire dose range studied. The implantation to doses of 5 × 1014 and 5 × 1015 cm–2 led to the appearance of an additional peak on XRD curves, which was related to the formation of a stressed GaAs layer with positive deformation arising due to the formation of point-defect clusters. The implantation to a dose of 5 × 1016 cm–2 led to the formation of a dense structure of extended defects in the implanted layer, which was accompanied by the relaxation of macrostresses to the initial state.

Secondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N+ ions at doses of 5 × 1014–5 × 1016 cm–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.

AbstractSecondary-ion mass spectrometry and Rutherford proton backscattering have been used to measure the concentration profiles of nitrogen atoms and examine the defect structure of epitaxial GaAs layers implanted with 250-keV N^+ ions at doses of 5 × 10^14–5 × 10^16 cm^–2. It was found that no amorphization of the layers being implanted occurs at doses exceeding the calculated amorphization threshold, a concentration of point defects that is formed is substantially lower than the calculated value, and a characteristic specific feature of the defect concentration profiles is the high defect concentration in the surface layer.

An investigation of mechanisms of enhancement of irradiation-induced damage formation in GaN under molecular in comparison to monatomic ion bombardment is presented. Ion-implantation-induced effects in wurtzite GaN bombarded with 0.6 keV amu(-1) F, P, PF2, PF4, and Ag 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/disordered layer formed at the sample surface. In all the cases studied, a shift to molecular ion irradiation from bombardment by its monatomic constituents enhances the damage accumulation rate. Implantation of a 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 compared to the others. These findings show that the higher probability of formation of large defect clusters is important mechanism of the enhancement of stable damage formation in GaN under molecular, as well as under heavy monatomic ion irradiation.