Radiation Defects in Heavily Irradiated GaAs

TEM and HAADF STEM Imaging of Dislocation Loops in Irradiated GaAs

“…and co-workers concluded that the loop-like defects on {110} planes present in 300 keV proton bombarded (10 15 to 10 16 H + cm −2 ) n-type Si-doped GaAs annealed in the range 500 • C to 900 • C were hydrogen filled vacancy loops (called hydrogen platelets) [3][4][5] which, due to the gas pressure inside the loops, would appear to be of interstitial nature [3]. This conclusion was supported by still earlier reports of vacancy loops on {110} planes observed in Si-and Te-doped GaAs annealed at high temperatures [6][7][8] and the fact that for low dose electron irradiated n-type GaAs, pointdefect annealing already occurs in the temperature range 200 to 300 • C, which is evidence for point defect mobility in this temperature range [9]. The new data presented in this paper allows for a reinterpretation of the older defect models in proton bombarded n-type GaAs, i.e.…”

“…Since the annealing stages of the electrical properties of irradiated n-type GaAs were found to be dependent on the radiation induced point defect concentrations [9], annealing stages of electrical properties reported for electron and neutron irradiated n-type GaAs differed [14,15]. For electron irradiated n-type GaAs, it was proposed that the annealing stages of electrical properties comprise firstly of point defect annealing and clustering that takes place at about 200-300 • C, and secondly the annealing of clusters which take place in the 400-600 • C temperature range [9].…”

“…Since the annealing stages of the electrical properties of irradiated n-type GaAs were found to be dependent on the radiation induced point defect concentrations [9], annealing stages of electrical properties reported for electron and neutron irradiated n-type GaAs differed [14,15]. For electron irradiated n-type GaAs, it was proposed that the annealing stages of electrical properties comprise firstly of point defect annealing and clustering that takes place at about 200-300 • C, and secondly the annealing of clusters which take place in the 400-600 • C temperature range [9]. Although the authors of the current paper associate the formation of dislocation loops observed by TEM at 500 • C and above, with the final annealing stage of 400-600 • C for the electrical conductivity of electron irradiated n-type GaAs [9], it should be noted that the recovery of electrical conductivity would largely be related to the annealing of point defects (interstitial vacancy recombination) and dopants while the nucleation and growth of small interstitial dislocation loops would mostly involve the diffusion and coalescence of Ga and As interstitials to sinks acting as nucleation centers for dislocation loops.…”

“…For electron irradiated n-type GaAs, it was proposed that the annealing stages of electrical properties comprise firstly of point defect annealing and clustering that takes place at about 200-300 • C, and secondly the annealing of clusters which take place in the 400-600 • C temperature range [9]. Although the authors of the current paper associate the formation of dislocation loops observed by TEM at 500 • C and above, with the final annealing stage of 400-600 • C for the electrical conductivity of electron irradiated n-type GaAs [9], it should be noted that the recovery of electrical conductivity would largely be related to the annealing of point defects (interstitial vacancy recombination) and dopants while the nucleation and growth of small interstitial dislocation loops would mostly involve the diffusion and coalescence of Ga and As interstitials to sinks acting as nucleation centers for dislocation loops. The results of this paper indicate that this latter process (as observed by TEM) is what other workers [9] referred to as "disordered-region annealing" (from electrical conductivity measurements).…”

“…The current paper compares earlier TEM results of dislocation loops generated in n-type GaAs by 1 MeV electron and fast neutron irradiation with recent Cs-corrected (245) HAADF STEM imaging of {110} and {111} dislocation loops in neutron irradiated and annealed n-type GaAs. The annealing stage where radiation induced interstitial atoms coalesce to form dislocation loops visible in TEM, is correlated qualitatively with the final annealing stage of the electrical conductivity of electron irradiated n-type GaAs [9].…”