We investigate electronic transport properties of as-grown and annealed n-type modulationdoped Al 0.15 Ga 0.85 As/GaAs 1−x Bi x (x=0 and 0.04) quantum well (QW) structures using magnetotransport measurements in the temperature range 4.2 K and 60 K and at magnetic fields up to 18 T. Thermal annealing process was applied at two different temperatures, 700 °C and 350 °C during 60 s and 180 s, respectively. We find that electron effective mass and 2D electron density in as-grown Bi-containing sample are slightly lower than that in Bi-free one. Furthermore, quantum electron mobility and quantum scattering time are observed to be decreased in Bi-containing samples. The annealing process at 700 °C causes a slight increase in electron effective mass and 2D electron density. A negligible decrease in electron effective mass and an increase in 2D electron density are determined following annealing at 350 °C. The observed change in electron effective mass following thermal annealing process is attributed to changing 2D electron density in the samples. No improvement on quantum electron mobility and quantum scattering time are observed following thermal annealing at both process temperatures. We determine that one electron subband (e1) for as-grown and annealed (at 700 °C for 60 s) Bicontaining QWs and two electron subbands (e1 and e2) for the annealed (at 350 °C for 180 s) GaAsBi QW sample and the Bi-free QW sample contribute to electronic transport. Our results reveal that there is no significant direct effect of Bi on effective electron mass, but an indirect effect, in which Bi can provoke changes in 2D electron density and hence causes not to observe actual band-edge electron mass but a deviation from its band-edge value. Therefore, it can be concluded that dispersion curve of conduction band does not change as an effect of Bi incorporation in GaAs.

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We demonstrate a new semiconductor quantum system based on GaSb quantum dots (QDs) embedded in single-crystalline AlGaSb matrix by filling droplet-etched nanoholes. The dropletmediated growth mechanism allows formation of low QD densities required for non-classical singe-QD light sources. The photoluminescence (PL) experiments reveal that the GaSb QDs have an indirect-direct bandgap cross-over at telecom wavelengths. This is due to the alignment of the Γ and L valleys in the conduction band as a result of quantum confinement controlled by dimensions of the nanostructure. We show that in the direct bandgap regime close to 1.5 µm wavelength, the GaSb QDs have a type I band alignment and exhibit excitonic emission with narrow spectral lines and very low inhomogeneous broadening of PL emission owing to the high material quality and dimensional uniformity. These properties are extremely promising in terms of applications in infrared quantum optics and quantum photonic integration.

In this work, we have investigated the structural and optical properties of GaAs (1x) Bi x /GaAs single quantum wells (QW) grown by molecular beam epitaxy (MBE) on GaAs (311)B substrates using x-ray diffraction (XRD), atomic force microscopy (AFM), Fourier-transform Raman (FT-Raman) and photoluminescence (PL) spectroscopy techniques. The FT-Raman results revealed a decrease of the relative intensity ratio of transverse (TO) and longitudinal (LO) optical modes with the increase of Bi concentration which indicates reduction of the structural disorder with increasing Bi incorporation. In addition, the PL results show an enhancement of the optical efficiency of the structures as the Bi concentration is increased due to important effects of exciton localization related to Bi defects, non-radiative centers and alloy disorder. These results provide evidence that Bi is incorporated effectively in the QW region. Finally, the temperature dependence of PL spectra has evidenced two distinct types of defects related to the Bi incorporation, namely Bi clusters and pairs, and alloy disorder and potential fluctuation.

We report on the power loss mechanisms of hot electrons in as-grown and annealed n-type modulation-doped Al 0.15 Ga 0.85 As/GaAs 1-x Bi x (x = 0 and 0.04) quantum well structures considering acoustic phonon interactions via the deformation potential (non-polar) and piezoelectric (polar) scatterings. The two-dimensional (2D) electron gas is heated by applying various electric fields under a steady-state magnetic field, and the effect of the applied electric field on the Shubnikov de Haas (SdH) oscillations is analyzed to investigate the power loss mechanism. The temperature of hot electrons (T e ) has been obtained by comparing the lattice temperature and applied electric field dependencies of the SdH oscillation amplitude. The hot electron temperature is almost the same for both Bi-free and Bi-containing samples except for the sample annealed at a higher temperature (700 • C) than the growth temperature of GaAsBi. The electron temperature dependence of power loss is analyzed using current theoretical analytic models derived for 2D semiconductors. We find that energy relaxation occurs in the intermediate temperature regime, including mixing of piezoelectric and deformation potential scattering. The power loss of hot electrons is found to be proportional to (T γ e − T γ L ) with γ in the range from 2.4 to 4.2, which indicates that the hot electron relaxation is due to acoustic phonon scatterings via unscreened deformation potential and piezoelectric scattering. It is found that deformation potential scattering is dominant over piezoelectric scattering in the Bi-free sample, while the incorporation of Bi into the GaAs lattice makes these processes comparable. After thermal annealing at lower than growth temperature (350 • C), the scattering mechanism switches from deformation potential to piezoelectric scattering. After thermal annealing at higher than growth temperature (700 • C), the theoretical model does not fit to the experimental results due to degradation of the sample.