Deep-level defects in n-type GaAs1−xBix having 0 ≤ x ≤ 0.023 grown on GaAs by molecular beam epitaxy at substrate temperature of 378 °C have been injvestigated by deep level transient spectroscopy. The optical properties of the layers have been studied by contactless electroreflectance and photoluminescence. We find that incorporating Bi suppresses the formation of GaAs-like electron traps, thus reducing the total trap concentration in dilute GaAsBi layers by over two orders of magnitude compared to GaAs grown under the same conditions. In order to distinguish between Bi- and host-related traps and to identify their possible origin, we used the GaAsBi band gap diagram to correlate their activation energies in samples with different Bi contents. This approach was recently successfully applied for the identification of electron traps in n-type GaAs1−xNx and assumes that the activation energy of electron traps decreases with the Bi (or N)-related downward shift of the conduction band. On the basis of this diagram and under the support of recent theoretical calculations, at least two Bi-related traps were revealed and associated with Bi pair defects, i.e. (VGa+BiGa)−/2− and (AsGa+BiGa)0/1−. In the present work it is shown that these defects also influence the photoluminescence properties of GaAsBi alloys.
Deep level transient spectroscopy (DLTS) has been applied to study electron and hole traps in InPBi alloys with 2.2 and 2.4% Bi grown by molecular beam epitaxy. One donor-like trap with the activation energy of 0.45–0.47 eV and one acceptor-like trap with activation energy of 0.08 eV have been identified in DLTS measurements. For the reference sample (InP grown at the same temperature), the deep donor trap has also been observed, while the acceptor trap was not detected. According to the literature, the deep donor level found in InP(Bi) at 0.45–0.47 eV below the conduction band has been attributed to the isolated PIn defect, while the second trap, which is observed only for Bi containing samples at 0.08 eV above the valence band can be attributed to Bi clusters in InPBi. This acceptor level was proposed to be responsible for the observed partial compensation of native free electron density in InPBi layers. It is also shown that the deep donor traps are active in photoluminescence (PL). A strong radiative recombination between donor traps and the valence band are observed in PL spectra at energy 0.6–0.8 eV, i.e. ~0.47 eV below the energy gap of InPBi, which is determined by contactless electroreflectance.
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