Positron-lifetime study of compensation defects in undoped semi-insulating InP

Abstract

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 $282\ifmmode\pm\else\textpm\fi{}5 \mathrm{ps}$ which we associate with either the isolated indium vacancy ${V}_{\mathrm{In}}^{3\ensuremath{-}}$ or related hydrogen complexes. The shallow donor complex ${V}_{\mathrm{In}}{\mathrm{H}}_{4},$ 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 $950\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ in conjunction with the disappearance of the ${V}_{\mathrm{In}}{\mathrm{H}}_{4}$ infrared-absorption signal, trapping into ${V}_{\mathrm{In}}$-related centers is observed to increase slightly, and an additional positron trapping defect having a lifetime of 330 ps appears at a concentration of $\ensuremath{\sim}{10}^{16} {\mathrm{cm}}^{\ensuremath{-}3},$ indicating divacancy trapping. These results support the recent suggestion that the ${V}_{\mathrm{In}}{\mathrm{H}}_{4}$ complex present in as-grown InP dissociates during annealing, forming ${V}_{\mathrm{In}}{\mathrm{H}}_{n}^{(3\ensuremath{-}n)\ensuremath{-}}(0l~nl~3)$ complexes and that the recombination of ${V}_{\mathrm{In}}$ with a phosphorus atom results in the formation of EL2-like deep donor ${\mathrm{P}}_{\mathrm{In}}$ antisite defect, which compensates the material. It is suggested that the divacancy formed on annealing is ${V}_{\mathrm{In}}{V}_{\mathrm{P}},$ and that this defect is probably a by-product of the ${\mathrm{P}}_{\mathrm{In}}$ antisite formation.