Transmission Electron Microscopy of Be Implanted Si-Doped GaAs

Abstract

Be ions were implanted into degenerately Si-doped GaAs at 300 keV to a dose of 10 15 cm À2 . The region near the projected range remained crystalline, and subthreshold defects formed at this depth after annealing at 450-500 C. The defects are identified as circular prismatic perfect interstitial loops on the {110} planes, originating after the annealing of defect clusters near 400 C. The Burgers vector of these loops was computed using the comparison of experimental and computed defect intensity profiles. The formation of only interstitial loops is attributed to the dislocation bias effect, whereby interstitials are attracted more strongly to dislocations than vacancies. A high density of small loops with {110} and {111} habit planes were observed to form slightly shallower than the projected range after annealing at 600 C and extend closer to the surface after annealing at 700 C. The density of these loops decreased, and their size increased, after annealing at 800 C. However, they remained small compared to the loops near the projected range. A shift of the loop area per unit volume profile slightly deeper into the material after annealing at 600 C or higher (as compared to annealing at 500 C) resulted from the formation of loops as interstitials diffused deeper into the material, while interstitials diffusing to shallower regions were annihilated by the excess vacancy concentration in this region developed due to knock-on during implantation. The decreased size of the loops found in this study as compared to those reported previously is suggested to be as a result of the use of degenerately Si-doped rather than semi-insulating GaAs.

Parallelogram-Shaped and Triangular Defects in GaAs

“…These typical subthreshold defects have been discussed [1], and of interest here are parallelogram-shaped, triangular and line-like defect images also found occasionally in these samples. These typical subthreshold defects have been discussed [1], and of interest here are parallelogram-shaped, triangular and line-like defect images also found occasionally in these samples.…”

“…A recent study of high dose (10 15 cm À2 ) Be implanted Si-doped GaAs showed that extended defects formed only after annealing at 450-500 C and that most of the defects were circular interstitial prismatic dislocation loops on the {110} planes [1]. These are typical subthreshold implantation defects, which form in implanted material prior to amorphization (usually after annealing).…”