Positron-annihilation study of compensation defects in InP

Abstract

Positron-annihilation lifetime and positron-annihilation Doppler-broadening (PADB) spectroscopies have been employed to investigate the formation of vacancy-type compensation defects in n-type undoped liquid encapsulated Czochrolski grown InP, which undergoes conduction-type conversions under high temperature annealing. N-type InP becomes p-type semiconducting by short time annealing at 700 °C, and then turns into n-type again after further annealing but with a much higher resistivity. Long time annealing at 950 °C makes the material semi-insulating. Positron lifetime measurements show that the positron average lifetime τav increases from 245 ps to a higher value of 247 ps for the first n-type to p-type conversion and decreases to 240 ps for the ensuing p-type to n-type conversion. The value of τav increases slightly to 242 ps upon further annealing and attains a value of 250 ps under 90 h annealing at 950 °C. These results together with those of PADB measurements are explained by the model proposed in our previous study. The correlation between the characteristics of positron annihilation and the conversions of conduction type indicates that the formation of vacancy-type defects and the progressive variation of their concentrations during annealing are related to the electrical properties of the bulk InP material.