Investigation of defects in gallium arsenide using positron annihilation

Abstract

Grown-in defects in undoped GaAs, silicon-doped GaAs, and cadmium-doped GaAs have been investigated by positron-lifetime measurements. Trapping by vacancylike defects is observed in both undoped and silicon-doped GaAs, while no trapping occurs in cadmium-doped samples. The positron lifetime in these samples is 220 ps. The lifetime of trapped positrons in undoped GaAs is 290 ps, while in silicon-doped GaAs it is 260 ps. The 290-ps lifetime component is interpreted to arise from a monovacancy-impurity complex and the 260-ps component from annihilation at a substitutional silicon site. Room-temperature measurements on samples isochronally annealed up to 750°C show removal of defects in undoped GaAs at approximately 500°C. At higher annealing temperatures a new defect is created which yields a lifetime of only 225 ps. Similar observations pertain to silicon-doped GaAs except that no annealing stage is evident at 500°C. It is proposed that the thermally created defect is a gallium antisite defect. Measurements in the (20-300)-K temperature range show that the trapping rate of the positrons increases roughly exponentially with increasing temperature in contrast to the case of silicon. A thermally activated trapping mechanism is proposed with activation energies appropriate to the defect in question. For the gallium antisite defect the activation energy is approximately 200 meV, about 60 meV for the substitutional silicon site, and 40 meV for the monovacancy-impurity complex.