Abstract
A comparative study of laser and thermal annealing of Zn and Cd ion implanted GaAs is presented in this thesis. The techniques used were Rutherford backscattering, transmission electron microscopy, Hall effect and sheet resistivity measurements. The variation in the properties of the implanted GaAs with implantation temperature, ion dose, ion energy and annealing temperature were investigated. For laser annealing they were studied as a function of laser pulse length, laser energy density and multiple irradiations. For the thermal annealing process, the results indicated that an annealing temperature of 900°C was needed for perfect recrystallization and maximum electrical (~86%) activation. In the temperature range 650 to 800°C the sheet hole concentration increased with increasing dose up to a dose of about 1x10[14] Zn[+] /cm[2] and above this dose it saturated between (1-2)x10[14] holes/cm[2] when implanted at room temperature. Results were similar for implant energies of 60 to 450 keV. For samples implanted at 200°C, the sheet hole concentration increased with increasing dose and the maximum value observed was in the range (1-2)x10[19] holes/cm3. Irradiation with a freely generated ruby laser produced electrical activities from about 27% to 50% and peak concentrations from about 1x10[19] to 7x10[19] holes/cm[3]. RBS measurements showed that residual damage still remained in these samples. In contrast a Q-switched ruby laser pulse produced complete recrystallization (X[min] = 4%) with electrical activities up to 100%. The highest peak hole concentration was measured to be about 1x10[20] holes/cm[3]. Profiles of the implanted ions are shown to depend on most of the parameters mentioned above. The possible explanations for the diffusion of Zn and Cd in thermal annealing and laser annealing samples are discussed.