Positron-lifetime study of compensation defects in undoped semi-insulatingInP

Positron-lifetime and infrared-absorption spectroscopies have been used to investigate the compensation defects that render undoped n-type liquid enca psulated Czochralski-grown InP semi-insulating under high-temperature annea ling. The positron measurements, carried out over the temperature range of 25-300 K, reveal in the as-grown material a positron Lifetime of 282+/-5 ps which we associate with either the isolated indium vacancy V-In(3-) or rel ated hydrogen complexes. The shallow donor complex VInH4, responsible for m uch of the n-type conductivity and the strong infrared absorption signal at 4320 nm, is ruled out as a significant trapping site on the grounds that i ts neutral state is present at too low a concentration. After annealing at 950 degrees C, in conjunction with the disappearance of the VInH4 infrared- absorption signal, trapping into V-In-related centers is observed to increa se slightly, and an additional positron trapping defect having a lifetime o f 330 ps appears at a concentration of similar to 10(16) cm(-3), indicating divacancy trapping. These results support the recent suggestion that the V InH4 complex present in as-grown InP dissociates during annealing, forming VInHn(3-n-) (0 less than or equal to n less than or equal to 3) complexes a nd that the recombination of VI, with a phosphorus atom results in the form ation of EL2-like deep donor P-In antisite defect, which compensates the ma terial. It is suggested that the divacancy formed on annealing is VInVP, an d that this defect is probably a by-product of the P-In antisite formation. [S0163-1829(98)02044-X].