Positron-lifetime and infrared-absorption spectroscopies have been used to investigate the compensation defects that render undoped n-type liquid encapsulated Czochralski-grown InP semi-insulating under high-temperature annealing. 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 3- In or related hydrogen complexes. The shallow donor complex V InH 4, responsible for much 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 its neutral state is present at too low a concentration. After annealing at 950°C, in conjunction with the disappearance of the V InH 4 infrared-absorption signal, trapping into V In-related centers is observed to increase slightly, and an additional positron trapping defect having a lifetime of 330 ps appears at a concentration of ∼10 16 cm -3, indicating divacancy trapping. These results support the recent suggestion that the V InH 4 complex present in as-grown InP dissociates during annealing, forming V InH (3-n)- n (0≤n≤3) complexes and that the recombination of V In with a phosphorus atom results in the formation of EL2-like deep donor P In antisite defect, which compensates the material. It is suggested that the divacancy formed on annealing is V InV P, and that this defect is probably a by-product of the P In antisite formation.
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