Defect identification in GaAs grown at low temperatures by positron annihilation

Abstract

We use positron annihilation to study vacancy defects in GaAs grown at low temperatures ͑LT-GaAs͒. The vacancies in as-grown LT-GaAs can be identified to be Ga monovacancies, V Ga , according to their positron lifetime and annihilation momentum distribution. The charge state of the vacancies is neutral. This is ascribed to the presence of positively charged As Ga ϩ antisite defects in vicinity to the vacancies. Theoretical calculations of the annihilation parameters show that this assignment is consistent with the data. The density of V Ga is related to the growth stoichiometry in LT-GaAs, i.e., it increases with the As/Ga beam equivalent pressure ͑BEP͒ and saturates at 2ϫ10 18 cm Ϫ3 for a BEPу20 and a low growth temperature of 200°C. Annealing at 600°C removes V Ga . Instead, larger vacancy agglomerates with a size of approximately four vacancies are found. It will be shown that these vacancy clusters are associated with the As precipitates formed during annealing.

Direct identification of As vacancies in GaAs using positron annihilation calibrated by scanning tunneling microscopy

“…7 In a recent study, we measured the annihilation momentum distribution for pure metallic As and As precipitates in nonstoichiometric GaAs layers. 27 The shape of the momentum distribution was in agreement with that for V Ga -Si Ga as shown in Fig. 3, supporting our conclusions.…”

Ga Sublattice Defects in (Ga,Mn)As: Thermodynamical and Kinetic Trends

“…The slope of the line is a fingerprint of a specific vacancy. Figure 3 shows the line connecting the bulk and the S; W parameters [1.021(3), 0.73(1)] specific to V Ga [6,9]. The measured points fall on the line, thus giving evidence that the observed vacancy defect is the Ga vacancy.…”

Defects in the GaAs and InGaAs layers grown by low-temperature molecular-beam epitaxy

“…If in accordance with [25], we assume V Ga 3-to be a dominating acceptor defect in LT-GaAs, the V Ga concentration should be no lower than 3·10 18 cm -3 to compensate the Si donors with a concentration of 1·10 19 cm -3 observed for a high concentration of excess arsenic. Much the same concentrations of gallium vacancies in LTGaAs are found in [27,28] by the method of positron annihilation. Thus, the experimental data show that the electrophysical and optical properties of LT-GaAs containing excess arsenic are mainly determined by As Ga and V Ga defects.…”

“…It can be assumed that the 0.95-1.0 eV band is related to the complexes including antisite arsenic, for example, As Ga -V Ga . Such complexes were earlier revealed in LT-GaAs by positron annihilation [27,28].…”