Abstract
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.
Highlights
We find that incorporating Bi suppresses the formation of GaAs-like electron traps, 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 hostrelated 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
The GaAs1−xBix epilayer compositions were determined from X-ray diffraction (XRD) rocking curves of the symmetrical (004) reflection, using the Cu Kα1 line
Summary
These traps manifest the lowest activation energies, in the ranges 0.07–0.1 eV and 0.15–0.19 eV respectively, depending on the Bi concentrations. The predicted defect energy level of (VGa + BiAs)2−/3− is reasonably consistent with recent DLTS experiments which estimated the energy position of the majority-electron trap E3 at about 0.23–0.28 eV below the conduction band in n-type GaAs1−xBix layers with 0.3% Bi, grown by MBE under intense UV illumination[44] Another deep-level defect detected in all of the present samples is called ET3. These measurements indicate that the revealed defects, beside the control of electrical properties, influence the photoluminescence properties of GaAsBi alloys
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