Point defects in GaAs studied by correlated positron lifetime, optical, and electrical measurements

Abstract

Positron lifetime measurements are used in combination with optical (infrared absorption, photo‐luminescence, and photoreflexion) and electrical (Hall and resistivity) investigations to study native point defects and their complexes in as‐grown GaAs crystals. In undoped n‐type GaAs which contains 2 × 1016 cm−3 EL2° centres strong positron trapping by a vacancy‐type defect is detected. The point defect is discussed as a vacancy in the As sublattice appearing in a neutral or negative charge state, V As0,−. In heavily doped GaAs dopant‐vacancy complexes of the type AV As+ and DV Ga− are identified from optical measurements in p‐type and n‐type crystals, respectively. Positrons which are repelled by AV As+ are evidently trapped by acceptor‐type donor‐Ga vacancy complexes in n‐type GaAs. The decomposition of the lifetime spectra provides characteristic positron lifetimes of 295 ps and 260 ps for the V As0,− and DV Ga− defects, respectively. A specific positron trapping rate of 6 × 10−8 cm3 s−1 (3 × 1014 s−1) is estimated from the comparison of electrical and positron lifetime parameters and by identifying the compensating centres in heavily doped n‐type GaAs with DV Ga− defects. The number of grown‐in vacancies is discussed. Temperature dependent studies indicate a change in the nature of the dominating positron trap at low temperatures. Annealing experiments are discussed as a compensation of vacancies around 500 °C probably by in‐diffusion of acceptor‐type impurities.

Semi-insulating GaAs: A possible substrate for a field-assisted positron moderator

“…In summary then, we view the positrons as drifting towards the contact, where they are trapped into some long-lived interface state. This picture is quite consistent with the observation that in SI-GaAs bulk, positrons are normally not observed to trap into any vacancy defect states [26].…”