Damage evolution in low-energy ion implanted silicon

Abstract

The annealing of damage generated by low-energy ion implantation in polycrystalline silicon ͑poly-Si͒ and amorphous silicon ͑a-Si͒ is compared. The rate of heat release between implantation temperature and 350-500°C for Si implanted in both materials and for different ions implanted in poly-Si shows a very similar shape, namely, a featureless signal that is characteristic of a series of processes continuously distributed in terms of activation energy. Nanocalorimetry signals differ only by their amplitude, a smaller amount of heat being released after light ion implantation compared to heavier ones for the same nominal number of displaced atoms. This shows the importance of dynamic annealing of the damage generated by light ions. A smaller amount of heat is released by implanted poly-Si compared to a-Si, underlining the effect of the surrounding crystal on the dynamic annealing and the relaxation of the defects. Damage accumulation after 30-keV Si implantation is also characterized by Raman scattering and reflectometry, featuring a similar trend in a-Si, poly-Si, and monocrystalline silicon ͑c-Si͒ with a saturation around 4 Si/ nm 2. Considering these results together with other recent experiments in c-Si and molecular dynamic simulations, it is concluded that the damage generated by low-energy ion implantation that survives dynamic annealing is structurally very similar if not identical in both crystalline and amorphous silicon, giving rise to the same kind of processes during a thermal anneal. However, the damage peak obtained by channeling saturates only above 10 Si/ nm 2. This suggests that between 4 and 10 Si/ nm 2 , further damage occurs by structural transformation without the addition of more stored energy.

Structural relaxation kinetics for first- and second-order processes: Application to pure amorphous silicon

“…Similar thermograms have been measured for other amorphous materials, such as ball milled silicon [3], metallic powders [4] and supercooled alloys [5,6]. The characteristic unstructured signal of structural relaxation is also found in crystalline materials with a high concentration of non-equilibrium point or line defects: cold worked metals [7] and irradiated materials [8]. In these cases the low-temperature transformation is known as recovery.…”

Evolution of the Potential-Energy Surface of Amorphous Silicon

“…Using ART nouveau [8], a saddle-point finding method, we characterize the evolution of the local energy landscape, defined by the distribution of transition states and adjacent energy minima around a local configuration, as a function of relaxation. The resulting theoretical picture can be used to understand and explain recent nano-calorimetric measurements on ion-implanted a-Si samples [5,6].Our a-Si model is relaxed using the Stillinger-Weber potential with parameters adjusted specifically to recover the structural and vibrational properties of the amorphous system [9]. While this potential has a number of shortcomings, its structural evolution as a function of relaxation is in good qualitative agreement with experiment as discussed below.…”

“…In spite of these contributions, many questions remain regarding the evolution of the local structure of the energy landscape itself as a function of relaxation, an evolution that determines the dynamics of disordered materials away from equilibrium [5]. For example, following measurements of heat released during the annealing of damage generated by low-energy ion implantation in amorphous silicon, it was suggested that the activation energy and the amount of heat released are uncorrelated [5,6], microscopic details were still missing, however, as well as a general picture of the phenomenon. Results presented here tie experiments and simulations and provide a clear link between the structure of the energy landscape and experimental observations, supporting the importance of this concept.More precisely, we focus on amorphous silicon, a model system studied extensively, both experimentally and theoretically, over the years [4,5,7].…”

“…For example, following measurements of heat released during the annealing of damage generated by low-energy ion implantation in amorphous silicon, it was suggested that the activation energy and the amount of heat released are uncorrelated [5,6], microscopic details were still missing, however, as well as a general picture of the phenomenon. Results presented here tie experiments and simulations and provide a clear link between the structure of the energy landscape and experimental observations, supporting the importance of this concept.More precisely, we focus on amorphous silicon, a model system studied extensively, both experimentally and theoretically, over the years [4,5,7]. Using ART nouveau [8], a saddle-point finding method, we characterize the evolution of the local energy landscape, defined by the distribution of transition states and adjacent energy minima around a local configuration, as a function of relaxation.…”

Gold nanoparticles resist deformation by swift heavy ion irradiation when embedded in a crystalline matrix

“…It has been reported that damage accumulation reduces the intensity of characteristic peaks [14] and that compressive (tensile) strain shifts phonon modes to higher (lower) frequencies with respect to their bulk values [15,16]. The expected bulk values corresponding to the AlAs and GaAs LO-peaks are 401.5 and 292.1 cm À1 respectively.…”