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We use a low-energy positron beam to study the influence of doping and stoichiometry on the native defects in GaAs grown by molecular-beam epitaxy at 250 °C. Ga vacancies are identified in all samples by measuring the momentum distribution of annihilating core electrons. The charge of VGa is negative in Si-doped samples but neutral in undoped and Be-doped material. We propose that the Ga vacancies are complexed with As antisites in undoped and Be-doped samples and with Si impurities in n-type material. The concentration of Ga vacancies depends on the doping and stoichiometry of growth conditions. It follows generally the trends in the VGa formation energy as a function of the Fermi level position and stoichiometry. The strong loss of free carriers in the As-rich Si-doped samples is attributed to the formation of Ga vacancy complexes, negative ion defects and inactive clusters of Si atoms.

Ion-implantation is a widely used doping technique in II–VI semiconductors. Nevertheless, ion-implantation damage has to be better understood to properly control this process. In order to investigate the implantation-induced defects in such compounds, room-temperature implantations of 320 keV Al ions have been performed on crystalline samples of [111] Hg1−xCdxTe (x≈20%) for doses ranging from 1013 to 1015 cm−2. We report the first measurements of x-ray diffuse scattering close to different Bragg reflections on such as-implanted samples. The evolution of the diffuse intensity as a function of the dose has been observed. The defect-induced diffuse intensity arises mainly from interstitial dislocation loops. Nevertheless, vacancy loops are observed above 3×1014 Al/cm2. The mean radius of the dislocation loops increases in size by three to four times when the dose rises from 1013 to 1015 cm−2. Finally, the saturation of point defects has been observed independently of their clustering at about 5×1013 Al/cm2, that is in the same range as the saturation dose of the sheet electron concentration.

We have used pulsed-slow-positron-beam-based positron lifetime spectroscopy to investigate the nature of acceptors and charge states of vacancy-type defects in low-energy proton-implanted 6H-SiC(H). We can infer from the temperature dependence of the lifetime spectra that neutral and negatively charged vacancy clusters exist in the track region. Depending on annealing, they give rise to positron lifetimes of 257±2, 281±4, and 345±2 ps, respectively. The 281 ps cluster likely has an ionization level near the middle of the band gap. By comparison with theory, the 257 and 280 ps are identified as (VC–VSi)2 and (VC–VSi)3 clusters, respectively. In addition, other acceptors of ionic type act as strong trapping centers at low temperature (T

Positron annihilation experiments have been performed to investigate the compensating defects in silicon δ-doping superlattices in (001) GaAs. The results reveal vacancies and ion-type defects, which are located between the delta planes in undoped GaAs. The vacancy defect is identified as the Ga vacancy and the negative ion is attributed to the Ga antisite. The concentrations of these defects increase strongly, when the areal concentrations of free carriers are reduced at the delta planes.

We used a slow positron beam to investigate the depth dependence of the positron–electron pair momentum distribution in ZnSe layers grown on a GaAs substrate. We report evidence that positrons annihilate in lattice in undoped ZnSe and at vacancies in heavily n-type ZnSe. It is also demonstrated that positrons in semi-insulating ZnSe are drifted to GaAs by fields of 1–3 kV/cm.

We show that two different types of photoquenching effect take place under low temperature illumination of lightly n‐type bulk GaAs. Both phenomena result in an increase in positron trapping at vacancies. The first associated with a decrease in EL2 absorption, is produced with light of 1.1 μm wavelength and recovers near 100 K. While little photoquenching related to EL2 is observed after illumination close to the band edge (0.83 μm), persistent increases in Hall voltage and positron lifetime accompanied by a decrease in near band‐edge absorption are observed. These latter phenomena recover at 50 K.

We show that positron trapping at negative As vacancies revealed under illumination in bulk semi‐insulating GaAs correlates with a form of near‐band‐edge absorption known as reverse contrast (RC). We conclude that it is the ionization of As vacancies to their negative charge state that gives rise to RC absorption.

We have performed positron annihilation experiments on CdTe films grown by vacuum evaporation at 220 °C on both plain glass and indium‐tin‐oxide‐coated glass substrates. By checking the linearity of the valence annihilation parameter S versus the core annihilation parameter W we introduce a method to analyze the data which directly shows that the same vacancy defect can be present in all the films. By comparing the core annihilation parameter at the defect to that at the VCd vacancy we can identify this defect as the divacancy VCd‐VTe. Its concentration in the films decreases from about 1018 to less than 1016 cm−3 after annealing in air at 400 °C for about 30 min. Chlorine doping seems to stabilize the divacancies.

Positron lifetime measurements have been used to study the recovery of electron irradiated GaAs between 77 and 800 K. Below room temperature positrons are trapped by vacancies in Ga sublattices. The Ga vacancies recover between 200 and 350 K.