Single-and multi-quantum well (QW) structures of Ga(AsBi)/GaAs with up to 10% Bi were grown by molecular beam epitaxy (MBE) at 300-330°C substrate temperature. The photoluminesce measurements of QW structures demonstrated room temperature emission up to wavelengths of ∼1.43 μm. In the structures obtained using a combined growth approach -an active layer with three QWs with ∼6% Bi was grown by MBE, whereas (AlGa)As claddings were grown by the metal organic vapour phase epitaxy technique -room temperature lasing at 1060 nm was documented.Introduction: It is expected that the introduction of novel dilute bismide alloys will lead to the achievement of efficient laser diodes at telecom and longer wavelengths with reduced power consumption, thus providing the benefits of a wide range of applications. For Ga(AsBi) alloys with Bi content larger than 10% grown on GaAs substrates, e.g. very large valence band spin-orbit-splitting exceeding the energy band gap E g can be achieved [1], which should help to suppress inter-valence-band absorption and dominant Auger recombination processes in telecom lasers. Optically pumped Ga(AsBi) lasers have already demonstrated promising device characteristics such as reduced temperature dependence of the lasing wavelength [2]. The first Ga (AsBi)/(AlGa)As single-quantum well (SQW) electrical injection laser was presented in [3]. The laser structure with 2.2% Bi in the well layer was grown by metal organic vapour phase epitaxy (MOVPE), and a room temperature emission wavelength of ∼947 nm was achieved. In this Letter, we present investigations of Ga(AsBi)/GaAs QWs and laser diode structures grown by molecular beam epitaxy (MBE). Strong photoluminescence (PL) signals have been observed in QWs with up to 10% Bi in the well region; room temperature lasing at the wavelength of 1060 nm was documented from the diode with three QWs with ∼6% Bi.

Article:Cechavicius, B., Kavaliauskas, J., Krivaite, G. et We present an optical study of beryllium ␦-doped GaAs/ AlAs multiple quantum well ͑QW͒ structures designed for sensing terahertz ͑THz͒ radiation. Photoreflectance ͑PR͒, surface photovoltage ͑SPV͒, and wavelength-modulated differential surface photovoltage ͑DSPV͒ spectra were measured in the structures with QW widths ranging from 3 to 20 nm and doping densities from 2 ϫ 10 10 to 5 ϫ 10 12 cm −2 at room temperature. The PR spectra displayed Franz-Keldysh oscillations which enabled an estimation of the electric-field strength of ϳ20 kV/ cm at the sample surface. By analyzing the SPV spectra we have determined that a buried interface rather than the sample surface mainly governs the SPV effect. The DSPV spectra revealed sharp features associated with excitonic interband transitions which energies were found to be in a good agreement with those calculated including the nonparabolicity of the energy bands. The dependence of the exciton linewidth broadening on the well width and the quantum index has shown that an average half monolayer well width fluctuations is mostly predominant broadening mechanism for QWs thinner than 10 nm. The line broadening in lightly doped QWs, thicker than 10 nm, was found to arise from thermal broadening with the contribution from Stark broadening due to random electric fields of the ionized impurities in the structures. We finally consider the possible influence of strong internal electric fields, QW imperfections, and doping level on the operation of THz sensors fabricated using the studied structures.

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Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, the Bi nanoparticles experience a transition to the direct-bandgap semiconducting state.

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