Preparation and characterization of semi-insulating undoped indium phosphide

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 degrees C) is sufficiently slow (around 30 degrees C h(-1)). However, the best semi-insulating properties (p > 10(7) Omega cm; mu approximate to 4000 cm(2) V-1 s(-1)) are achieved with a double anneal under vacuum of InP with residual carrier concentration less than 4 x 10(15) cm(-3). It is also shown that InP specimens with n approximate to 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'' accepters. It was also observed that annealed semi-insulating samples resumed the semiconducting 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.