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

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. In heavily doped GaAs dopant-vacancy complexes of the type AV and DV are identified from optical measurements in p-type and n-type crystals, respectively. Positrons which are repelled by AV 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 and DV 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 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.