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 hightemperature annealing. The positron measurements, carried out over the temperature range of 25-300 K, reveal in the as-grown material a positron lifetime of 282Ϯ5 ps which we associate with either the isolated indium vacancy V In 3Ϫ or related hydrogen complexes. The shallow donor complex V In 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°C, in conjunction with the disappearance of the V In H 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 ϳ10 16 cm Ϫ3 , indicating divacancy trapping. These results support the recent suggestion that the V In H 4 complex present in as-grown InP dissociates during annealing, forming V In H n (3Ϫn)Ϫ (0рnр3) 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 In V P , and that this defect is probably a by-product of the P In antisite formation.

Positron-annihilation study of compensation defects in InP

“…A positron lifetime component of 282 ps was observed and the corresponding trapping rate and defect concentration is found to be ϳ3.3ϫ10 8 s Ϫ1 and ϳ1.5ϫ10 16 cm Ϫ3 , respectively. 16 It has been revealed earlier that V In H 4 is the dominant shallow donor complex present in the as-grown InP and, on dissociation, positrons were found to be trapped at either V In defects or hydrogen-V In complexes, with a positron lifetime of 285 ps. 16,21 After a short time annealing, the V In H 4 complex dissociates into V In H n (nϪ3) (nϭ0,1,2,3) deep acceptorlike defects, turning the material into p-type conduction.…”

“…8,9 Studies of defect identification by positron annihilation in InP have been carried out intensively in recent years. [10][11][12][13][14][15][16] It has been found that positron average lifetimes of n-type materials are generally a few ps longer than those of p-type materials, indicating the presence of trapping defects. 11 However, we found in this study that there is a small increase of av after the n-type as-grown sample changes to p-type upon short time annealing at 700°C.…”

Modification of charge compensation in semi-insulating semiconductors by high energy light ion irradiation

“…There are strong absorption peaks between 600 and 700 cm −1 , which are due to two phonon processes, 34 and no change in the absorption peak intensities between 600 and 700 cm −1 indicates that HELI irradiation did not introduce crystal damage, 35 which are also supported by the observation of unchanged background absorption in the irradiated samples as compared to that of the unirradiated sample. 37 The concentration of this defect is estimated by various groups to be 10 16 -10 17 / cm 3 . 12,36 It is supported by the fact that in InP, grown by the LEC method using wet boric oxide as the encapsulant, water vapor dissociates and hydrogen is incorporated into the material.…”

Effects of annealing ambient on the formation of compensation defects in InP

“…24 Under the annealing process in a pure phosphorus ambient, producing one of the semiinsulating states of InP, the V In H 4 complex defect dissociated into V In H n (nϪ3) (nϭ0,1,2,3) deep acceptor-like defects. Since the Frenkel reaction is the major source of native point defects in InP, a large amount of V P vacancy and P In antisite defects form through the thermal diffusion of P atoms into V In vacancies.…”