Preparation and characterization of semi-insulating undoped indium phosphide

Abstract We show, for the first time, that undoped InP samples annealed in vacuum turn out to be semi-insulating if the cooling after the high temperature treatment (around 900 °C) is sufficiently slow (around 30 °C h −1 ). However, the best semi-insulating properties ( ϱ > 10 7 Ω cm ; μ ≈ 4000 cm 2 V −1 s −1 ) are achieved with a double anneal under vacuum of InP with residual carrier concentration less than 4 × 10 15 cm −3 . It is also shown that InP specimens with n ≈ 10 16 cm −3 can exhibit high resistivity, but lower mobility, after sequential thermal treatments. The conductivity conversion is ascribed to the overlap of two phenomena: (i) in-diffusion of deep impurities and (ii) generation-incorporation of “shallow” acceptors. It was also observed that annealed semi-insulating samples resumed the semi-conducting behavior after a second thermal treatment and quenching. This suggests that the concentration of both types of annealing-related levels are dependent on the cooling rate.