TEM and HAADF STEM Imaging of Dislocation Loops in Irradiated GaAs

Abstract

This paper compares earlier transmission electron microscopy results of dislocation loops generated in n-type GaAs by 1 MeV electron and fast neutron irradiation with recent Cs-corrected high angle annular dark field scanning transmission electron microscopy imaging of {110} and {111} dislocation loops in neutron irradiated and annealed (600 • C for 20 min) n-type GaAs. High angle annular dark field scanning transmission electron microscopy revealed that the {110} loop plane consists of two layers of Ga and As atoms, which is consistent with the model for a {110} pure-edge interstitial dislocation loop in GaAs. The loop plane of the {111} interstitial loop consists of one layer of Ga and As atoms while the stacking sequence across the loop is consistent with that of an extrinsic stacking fault. The projected positions of the Ga and As atom columns across the extrinsic stacking fault plane of the {111} loop indicate polarity continuation across the loop and the preservation of charge neutrality. The annealing stage at 500 • C found to be the minimum temperature for small dislocation loop formation visible in transmission electron microscopy, agrees with the final annealing stage of 400-600 • C for the electrical conductivity of electron irradiated n-type GaAs. It is proposed that {110} loops in proton bombarded GaAs are the same type of interstitial loops found in neutron irradiated GaAs while hydrogen platelets form on {111} planes in GaAs exposed to a hydrogen plasma at 180 • C or in high-dose proton bombarded GaAs.

Recovery and accumulation of ion irradiation damage leading to dose rate dependence in GaAs

“…56) Long range diffusion of interstitials were evidenced by cross-sectional transmission electron microscopy (TEM) observations combined with RBS/channeling for Si-ion irradiations at temperatures (88 °C-110 °C) higher than RT but definitely lower than 500 K; the ion irradiations at these slightly elevated temperatures brought about dense pileup of dislocations composed of agglomerated interstitials at far deeper regions than the ion range. 57) The defect diffusion at RT was also supported by the recent TEM observation that small defect clusters were formed by an in situ electron irradiation at RT but they did not appear at 50 K and the clusters at RT turned to interstitial-type dislocation loops when heated to 773 K. 58) The long-range migration accounts for the discrepancy in the observed recovery fraction between electrical and lattice-disorder measurements. When the carrier concentration is larger than that of the generated defects, the recovery is suppressed because the dopant atoms capture the moving defects to form immobile defect complexes, which again trap carriers.…”

Gradual degradation in InAs quantum dot lasers on Si and GaAs

“…They have specifically noted the appearance of small dislocation loops, believed to form due to clustering of point defects. 17–21…”

“…They have specifically noted the appearance of small dislocation loops, believed to form due to clustering of point defects. [17][18][19][20][21] In this work, we examine three types of InAs QD lasers epitaxially grown on silicon and GaAs substrates after extended constant-current aging, using electroluminescence (EL) imaging and scanning transmission electron microscopy (STEM) to determine the source of gradual degradation. EL dimming is largely uniform along the laser ridge with no enhanced dimming at the facets.…”