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Reflectance anisotropy spectroscopy (RAS) is applied to investigate GaAsBi samples grown by molecular beam epitaxy on (001)‐oriented GaAs substrates with GaAs or InGaAs buffer layers, resulting in nearly lattice‐matched or compressive strain conditions, with Bi concentration in the alloy in the range 2–5%. These new samples allow to bridge the gap in the Bi concentration values of previous RAS experiments (C. Goletti et al., Appl. Phys. Lett. 2022, 120, 031902), confirming the [110]‐polarized Bi‐related anisotropy in optical spectra below 3 eV and the linear dependence of its amplitude on Bi concentration. The characterization of the grown GaAsBi samples by X‐Ray diffraction and transmission electron microscopy clearly demonstrates the presence of CuPt‐like ordering in the bulk. CuPt structure is the primary origin of the optical anisotropy measured by RAS and by polarized photoluminescence, due to the anisotropic strain produced in the bulk crystal lattice. The lineshape of the RAS spectra above 3 eV, with its overall and characteristic positive convexity, confirms this conclusion. [ABSTRACT FROM AUTHOR]

5nm, 10nm and 20nm-thick GaInAsBi quantum wells were grown on the InP:Fe(100) substrates by molecular beam epitaxy. The top and bottom barriers of quantum structures were 50nm and 100nm-thick lattice-matched AlInAs, respectively. Quantum wells were grown at the substrate temperature of about 240°C. The maximum bismuth content in the wells was 5.0%. Transmission electron microscopy images revealed sharp interfaces between the wells and barrier layers as well as homogeneous Bi incorporation. Photoluminescence (PL) measurements demonstrated signals from all QW up to the room temperature. PL intensity was stronger in thinner quantum wells where relaxation and clustering effects were avoided. The longest emission wavelength registered reached 2.4µm. [ABSTRACT FROM AUTHOR]

Abstract: In this work the impact of doped GaAs buffer and cap layers on the bismide photoluminescence (PL) spectra has been studied. For this study three types of heterostructures were grown: a thin GaAsBi layer deposited directly onto the nominally undoped GaAs buffer layer, a GaAsBi layer grown onto the GaAs:Be layer, and a GaAsBi layer deposited onto the GaAs:Be layer and capped with the GaAs:Be layer. It has been demonstrated that p-type doping of the GaAs buffer and cap layers is resulting in a significant increase of the PL intensity. This enhancement was explained by a better photoexcited electron and hole confinement in the GaAsBi layer. [Copyright &y& Elsevier]

• A simple method for a reduction of the optical transition energy in quantum wells is suggested. • Additional GaInAs layers, inserted between GaInAsBi and AlInAs barriers, yield the ~0.4 µm redshift of the emission wavelength. • The experimental photo- and electroluminescence data agree with theoretical modelling. Light emitting diode structures of quaternary GaInAsBi bismide quantum wells with AlInAs barriers were grown on InP substrates by molecular-beam epitaxy. Intermediate additional layers of GaInAs were inserted between the bismide quantum wells and AlInAs barriers to reduce the electron size-quantization energy and, therefore, the energy of optical transitions. It has been demonstrated both theoretically and experimentally that the redshift of emission wavelength in the composite GaInAs 1− x Bi x (x ∼ 0.06) quantum wells with the additional intermediate GaInAs layers can be as large as ∼ 0.4 μ m. [ABSTRACT FROM AUTHOR]

Uni-Travelling-Carrier Photo-Diodes (UTC-PD) with GaAs1-xBix absorber layer have been fabricated and characterized. Two UTC-PD structures with and without a cliff layer between the absorber and collector were investigated. The spectral sensitivity dependences are similar for both UTC-PDs and are reaching the wavelength of 1.3 μm. Photosensitivity of structure with a cliff was one order of magnitude larger than that of the device without it. [ABSTRACT FROM AUTHOR]

The influence of thermal annealing on optical properties and carrier lifetime of dilute GaBixAs1-x layers was investigated. Thick (0.5-1.5 μm) relaxed and thin (30-100 nm) strained bismide layers were grown onto semi-insulating (100)-oriented GaAs substrates by molecular beam epitaxy (MBE) using As4 and As2, respectively. The post-growth annealing was carried out in the rapid thermal annealing (RTA) oven at the temperatures ranging from 550 °C to 750 °C under nitrogen atmosphere. The high resolution X-ray diffraction (HRXRD), photoluminescence (PL) and optical pump-THz probe measurements revealed two different GaBixAs1-x anneal mechanisms. The annealing at temperatures higher than 600 °C caused a significant reduction of carrier lifetime of relaxed bismide layers with x > 0.05. Meanwhile, thick layers with a smaller content of Bi (x < 0.05) and thin strained layers annealed up to 600 °C still exhibited long carrier lifetimes. On the other hand, the significant photoluminescence signal increase at room and liquid nitrogen temperatures was observed for the GaBiAs layers grown using As2 (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The GaAs1–xBix semiconductor alloy allows one to achieve large bandgap reduction and enhanced spin–orbit splitting energy at dilute Bi quantities. The bismide is currently being developed for near- to mid-infrared lasers, multi-junction solar cells, and photodetectors. In this structure–property relationship study of GaAsBi alloys, we report polarization dependent photoluminescence that reaches a polarization ratio up to 2.4 at room temperature. Polarization dependence is also presented using transmittance spectra, birefringence, and linear dichroism. The optical anisotropy observations agree with the predictions of point symmetry reduction in the CuPtB-type ordered GaAsBi phase. The structural ordering is investigated experimentally from the atomic scale in molecular-beam epitaxy (MBE) grown samples on exact and miscut (001) GaAs substrates, as well as on (001) Ge. The latter sample is composed of anti-phase domains in which the ordering axes are rotated by 90° angles. Since the conditions stabilizing the CuPtB ordered phase fall within the typical MBE growth regime of dilute bismides, the optical anisotropy in GaAsBi alloys is expected to be ubiquitous. These findings are important for the future development of GaAsBi-based optoelectronics and also provide new means to analyze structurally complex bismide alloys. [ABSTRACT FROM AUTHOR]

The strong photoluminescence (PL) signal at wavelengths ranging from 1,300 to 1,500 nm was observed in GaAsBi epitaxial layers grown by migration-enhanced epitaxy and annealed at $$600\,^{\circ }\hbox {C}$$ and higher temperatures. PL measurements at liquid helium temperatures showed two peaks at $$\sim $$ 0.9 and $$\sim $$ 1 eV. It was found that intensity of the higher energy peak decreases with temperature leaving only the lower energy peak at room temperature. Structural investigations demonstrated that annealing reduces Bi content in GaAsBi lattice by precipitating bismuth in nanometer-scale clusters. It is suggested that PL can be caused by the semimetal-semiconductor transition quantum confinement due to the quantum confinement effect in Bi clusters. [ABSTRACT FROM AUTHOR]

In this work the influence of technological parameters -- Tp substrate temperature and Bi flux -- on structural, electrical and optical properties of GaBiAs layers was investigated. Thin GaBiAs layers have been grown by molecular beam epitaxy technology on monocrystalline GaAs substrates. The surface morphology of GaBiAs layers and formation of Bi droplets were examined using atomic force microscopy. The lattice parameters of GaBiAs and Bi concentration have been evaluated from high resolution X-ray diffraction Δ(2Θ) spektra. Optical measurements showed the reduction of energy band gap from I. 15 to 0.86 eV for GaBiAs layers with 4.4 and 11.3% of Bi concentration. From the Hall effect measurements using Van der Pauw geometry the highest carrier concentration 3.2.1015 was measured for GaBiAs layers containing 11.3% of Bi. [ABSTRACT FROM AUTHOR]

Terahertz radiation pulses emitted after exciting semiconductor heterostructures by femtosecond optical pulses were used to determine the electron energy band offsets between different constituent materials. It has been shown that when the photon energy is sufficient enough to excite electrons in the narrower bandgap layer with an energy greater than the conduction band offset, the terahertz pulse changes its polarity. Theoretical analysis performed both analytically and by numerical Monte Carlo simulation has shown that the polarity inversion is caused by the electrons that are excited in the narrow bandgap layer with energies sufficient to surmount the band offset with the wide bandgap substrate. This effect is used to evaluate the energy band offsets in GaInAs/InP and GaInAsBi/InP heterostructures. [ABSTRACT FROM AUTHOR]