Transmission electron microscopy study on defects in arsenic-implanted mercury cadmium tellulide

Transmission electron microscopy (TEM) was used to study extended defects in arsenic-implanted HgCdTe (MCT). Implantation causes defects produced from ion bombardment. Annealing process is used for electrical activation and removing implantation damage. MCT was grown on (211) CdZnTe substrate by MBE method. Arsenic-doped MCT was implanted at room temperature with dual energies to the doses between 1x1010 to 1x1018 As + cm-3. Post isothermal annealing was performed at 436°C for 20 minutes and 250°C for 24 hr. Perfect and Frank dislocation loops were predominantly formed as the primary defects. The amount of the defects depended on a dosage. Extended defects were observed and the damage depth was beyond the ion projected range of implanted ions. No amorphous phase was found in implanted as-implanted MCT even at very high dose. The high degree of bond ionicity was responsible for defect combination to prevent amorphitization. Inside-outside contrast analysis was used for dislocation-loop nature analysis. The result shows that interstitial and vacancy loops were both found.; Thus, mercury vacancies, VHg and interstitials, Hgi which are knocked off by implantation are believed that the number of V Hg and Hgi could condense into form vacancies loops and interstitial loops. Arsenic dopant ions, As"i, could also coalesce into interstitial loops. Further annealing caused a change in the dislocation structure to edge dislocation half loops with Burgers vector of ½<110> inclined to the surface. The defects in the 250 °C annealed samples showed dislocation half loops, dislocation networks and remaining dislocation loops. By increasing temperature to 436 °C or increasing dose the half loops become more widespread. An explanation for the origin of dislocation formed during annealing could be referred to as ⅓<111> loops transform to ½<110> loops. The loops were continued to climb by absorption of point defects. The climb towards the surface would be expected since climb to the surface would remove the dislocation and this will decrease the energy which has extra half planes climb and then form half loops.