ABSTRACT Tunability of Landé g ‐factors associated with a single‐type of carrier in semiconductors remains a critical challenge, as precise control over spin physics is essential for advancing spintronic applications. At the same time, developing fast, field‐free tuning mechanisms is highly desirable. Here, we demonstrate that type‐II heterostructures provide an effective and scalable platform for robust optical manipulation of the g ‐factor using only the intensity of the incident light. By engineering wavefunction localization and overlap through the Coulomb attraction between spatially separated carriers, we have achieved a 1.5‐fold change in the excitonic g ‐factor solely by adjusting light intensity. Band structure simulations incorporating densities of photoexcited carriers confirm that this tuning mechanism arises from the delocalized carrier in the type‐II configuration. This approach enables a route for highly localized optical spin control, bridging a gap between spintronics and photonics. By eliminating the need for complex external fields, our findings open new avenues for g ‐factor engineering in well‐established semiconductor platforms.

III-Sb semiconductor nanostructures provide sophisticated materials for developing optoelectronic applications in the near-and midinfrared wavelengths, for which the capability of engineering band alignments and wave functions is highly desirable. Segregation and diffusion at the interfaces, however, are features commonly found in Sb-based structures, impacting device performance and optical properties. By using type-II GaAs1-xSbx/GaAs quantum wells as a platform, we demonstrate the effects of short-and long-range disorders in their optical emission, resulting in localization effects, broadening, and the emergence of a lower-energy band. The luminescence is characterized by varying excitation power, temperature, and magnetic field. Our findings demonstrate the presence of local potential minima of similar to 10 meV arising from the short-range contribution, the transition from correlated to uncorrelated electron-hole pair recombination, and the complex carrier dynamics in these systems.

AlInAs/AlGaAs quantum dots (QDs) have emerged as excellent emitters across the visible spectral range, showcasing highly tunable electronic properties through variations in composition and size. This versatility allows for diverse band alignments within the same system. In this study, we present compelling evidence for the coexistence of type-I indirect and direct emissions from QDs, supported by comprehensive analyses of their photoluminescence responses to excitation power, temperature, and time, along with band structure calculations. The high-density QD system exhibits signs of lateral coupling, facilitated by carrier transfer between dots, modulated by energy barriers and recombination times. Additionally, we can unequivocally prove that the QDs act as carrier reservoirs that progressively feed optically active states in the bulk GaAs at low temperatures & horbar;an attractive prospect for hot-carrier photovoltaics. Above certain temperatures, the bulk system reverts to the anticipated predominantly radiative recombination dynamics. Our theoretical framework, accounting for the coexistence of QD specimens with varying recombination times, successfully elucidates the optical response at different temperatures, emphasizing the pivotal role of QD excitation in enhancing the effective lifetime of carriers in the bulk.

•Nanoscale mapping of surface potential and current transport of InN nanostructures were performed by KPFM and c-AFM.•The downward band bending in the near-surface region of InN nanostructures is correlated with surface electron accumulation.•The Fermi level pinning by the surface states is observed.•The role of surface traps in the recombination of charge carriers on the nanometer scale has been evaluated.

The effects of growth rate on the structural, morphological, and electrical properties of InN nanostructures grown on [0001]-oriented GaN substrates by plasma-assisted molecular beam epitaxy is reported. Slowing the growth rate of the nanostructures resulted in extended time for reaching thermodynamically favored crystal facet structures, while at the same time extended the time during which the rf growth plasma can foster damage to the growth. Nanoscale mapping of surface potential and current transport were performed by Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C-AFM). The results show that increasing the growth rate by similar to 2.5 times results in more pronounced {10-15} facets of InN nanostructures and decreasing of the residual electron concentration from similar to 5.8 . 10(17) cm(-3) to similar to 2.5 . 10(17) cm(-3). This is explained by the direct bombardment of indium nitride with plasma species and enhanced decomposition, desorption of adatoms, and an increase in surface dangling bonds that creates surface states traps for electrons. The phenomena of electron accumulation in the near-surface region, as well as the current-voltage hysteresis curves under forward biases for InN nanostructures on GaN(0 0 0 1) substrate are disused.

A remote plasma enhanced chemical vapor deposition (CVD) process using GeH4, SiH4, and SnCl4 precursors has been developed for epitaxial growth of group-IV alloys directly on Si (100) substrates, without the need for buffer layers. X-ray diffraction measurements of a representative Ge1–xSnx sample which is 233 nm thick, with x = 9.6% show it to be highly oriented along the [001] direction and nearly relaxed, with 0.37% compressive strain. Ellipsometry measurements provide a pseudo-dielectric function which is well fitted by a 3-layer (substrate/alloy/surface oxide) model. Cross-sectional transmission-electron-microscope images show a highly defective interface layer, ∼ 60 nm thick, containing edge dislocations and stacking faults; above this layer, the lattice is well-ordered, with a much lower density of defects. Atomic force microscopy measurements show an RMS roughness of 1.2 nm for this film.

Silver nano-films with thicknesses of 5, 10 and 50 nm were grown using e-beam evaporation on glass substrates at room temperature in order to investigate their thermal nonlinear optical properties near surface plasmon resonance. The nonlinear response was verified using single beam z-scan setup in the cw regime. At 5 and 10 nm thickness, the films showed plasmonic resonance at 488 and 518 nm, respectively. The 50 nm films illustrated normal bulk behavior. Optical nonlinearities were stimulated at three different wavelengths, namely, 405, 532 and, 650 nm. Self-focusing and saturable absorption behavior was observed and compared at these wavelengths. The highest response was obtained at 532 nm close to the plasmonic wavelengths in both films. This behavior is related to the ultimate concentration of the optical power and hence, the temperature, to the nanometer range resulting in a large index change within a predicted time scale of sub-picoseconds. This outcome could pave the way for ultrafast thermal nonlinearity in nanomaterials. A discussion of this behavior and its consequence is presented.

Bullseye nanostructures with different central disk diameters and numbers of concentric rings have been fabricated in Au/Ag metallic films on glass substrates by focused ion beam milling. The Au/Ag bimetallic nanoresonator is expected to provide chemical stability and outstanding plasmonic property. A novel hybrid plasmonic emission has been observed by cathodoluminescence in the scanning electron microscope. It is found that the hybrid plasmon amplitude of the bullseye structure highly depends on the excitation position. The plasmonic intensity is the maximum when the beam is located at the edge of the central disk, and it can be tuned by selecting the disk size and the number of grooves. Additionally, the finite element simulation reveals that the bimetallic bullseye structure strongly confines the optical radiation, and the electric field distribution directly relates to the emission wavelength. Published by Elsevier B.V.

A magnetophotoluminescence study of the carrier transfer with hybrid InAs/GaAs quantum dot(QD)-InGaAs quantum well (QW) structures is carried out where we observe an unsual dependence of the photoluminescence (PL) on the GaAs barrier thickness at strong magnetic field and excitation density. For the case of a thin barrier the QW PL intensity is observed to increase at the expense of a decrease in the QD PL intensity. This is attributed to changes in the interplane carrier dynamics in the QW and the wetting layer (WL) resulting from increasing the magnetic field along with changes in the coupling between QD excited states and exciton states in the QW and the WL.

A 2D-to-3D transition from nanostructured films to multifaceted InN nanocrystals for growth on GaN(0001) is accompanied by a 30-fold enhancement of InN photoluminescence emission.

This work investigates the performance of an intermediate band solar cell (IBSC) structure based on InGaAs/GaAs lateral quantum wires under elevated temperature. Un-optimized structures using the same quantum wire based IB material have demonstrated an increase in solar conversion efficiency in comparison with reference GaAs P-I-N diode devices. In order to further understand the physics behind this increase, an optimized structure was developed and characterized. The External Quantum Efficiencies (EQE) of doped and Un-doped samples have been measured using these optimized designs. We present here the results of varying both applied bias and temperature on the EQE of these IBSC devices to highlight the advantages of such a structure.

Silicon carbide (SiC) power devices have been commercialized up to 1.7 kV with operating temperatures up to 573 K. The temperature limitations of SiC devices are generally derived from limitations in packaging and a lack of information on safe operating temperature regimes. Therefore, it is highly desirable to develop reliable temperature sensing techniques that can better take advantage of the SiC devices in high power applications. In this letter, ten gallium nitride (GaN)-on-SiC heterojunction diodes, aiming at high-power and high-temperature sensing applications, were fabricated using concentric ring geometry. These sensors can be monolithically integrated into GaN-on-SiC RF/Microwave power devices with fast-switching frequency and high-power density. The temperature dependent characteristics of the forward voltage drop at fixed current ( $V_{D}-{T}$ ) of these heterojunction devices and their sensitivities (mV/K) are comprehensively characterized in a temperature range from 300 to 650 K. These devices exhibit a high degree of linearity in their $V_{D}-{T}$ characteristics, which indicates the potential to be used as temperature sensors up to 650 K.

GaAsBi/GaAs double quantum well (DQW) heterostructures are grown at low temperatures using molecular beam epitaxy without growth interruption and studied by means of high-resolution x-ray diffraction and continuous wave photoluminescence (PL). Line shape analysis of PL spectra measured at various excitation densities allows reveals QW coupling due to tunnelling. It is shown that an efficient PL of GaAs/GaAs1−xBix/GaAs DQWs is significantly more thermally stable than that from a single quantum well (SQW) structure of similar composition. Such stabilization is described in terms of carrier redistribution between coupled quantum wells and is caused by carrier capture in the QW, thermal emission, and diffusion in the barrier.

Optical response of the indium arsenide (InAs)/gallium arsenide (GaAs) quantum dots (QDs) with a bimodal distribution is investigated through varying an initial GaAs capping layer between 35 and 18 monolayers. Photoluminescence (PL) measurements confirm that a thinner initial capping layer can reduce the QD dimensions and also modify the population ratio between the large QDs and the small QDs. Therefore, PL quenching related to QD dimension and carrier transfer between the bimodal QD populations has been affected. Manipulation of the initial GaAs capping layer provides a feasible approach to tailor the formation and optical performance of InAs QDs for optoelectronic device applications.

Selective doping of quantum dots is often used to improve efficiency of intermediate band solar cells (IBSC) due to IR harvesting and built-in-dot charge. To investigate the effects of the built-in-dot charge on recombination processes and device performance InAs/GaAs quantum dot IBSCs with direct Si doping in the quantum dots are fabricated, and the I-V characteristics and transients of the open circuit voltage and short circuit current are measured. The decay times of both the open circuit voltage and the short circuit current increase as the concentration of n-type doping increases in the quantum dots. The observed increase in the charge carrier lifetime is attributed to suppressed recombination of electron-hole pairs through the states of quantum dots and shrinking the depletion layer. This is supported by measurements of both photovoltage and photoluminescence spectra.

Electronic and optical properties of InAs/GaAs nanostructures grown by the droplet epitaxy method are studied. Carrier states were determined by k · p theory including effects of strain and In gradient concentration for a model geometry. Wavefunctions are highly localized in the dots. Coulomb and exchange interactions are studied and we found the system is in the strong confinement regime. Microphotoluminescence spectra and lifetimes were calculated and compared with measurements performed on a set of quantum rings in a single sample. Some features of spectra are in good agreement.

Photoelectric properties of laterally correlated multilayer InGaAs/GaAs quantum dots (QDs) heterostructures are studied. The response of the photocurrent to increasing excitation intensity is found to be nonlinear and varying with excitation energy. The structures are photosensitive in a wide range of photon energies above 0.6 eV. The spectral dependence of the photoconductivity (PC) is caused by strong interaction between the bulk GaAs and the lower energy states of the wetting layer, the QDs, as well as the defect states in the GaAs band gap. In particular, a mechanism for the participation of deep electron trap levels in the photocurrent is clarified. These structures also demonstrate a high sensitivity of up to 10 A/W at low excitation intensities. However, at higher excitation intensities, the sensitivity reduces exhibiting a strong spectral dependence at the same time. The observed sublinear PC dependence on excitation power results from a direct electron-hole recombination both in the QDs and in GaAs host. The solution of rate equations included the contributions of QD ground and exited states, bulk GaAs states and the states of defects within the GaAs bandgap describes well the experimental data.

Herein we investigate a (001)-oriented GaAs 1− x Bi x /GaAs structure possessing Bi surface droplets capable of catalysing the formation of nanostructures during Bi-rich growth, through the vapour-liquid-solid mechanism. Specifically, self-aligned “nanotracks” are found to exist trailing the Bi droplets on the sample surface. Through cross-sectional high-resolution transmission electron microscopy the nanotracks are revealed to in fact be elevated above surface by the formation of a subsurface planar nanowire, a structure initiated mid-way through the molecular-beam-epitaxy growth and embedded into the epilayer, via epitaxial overgrowth. Electron microscopy studies also yield the morphological, structural and chemical properties of the nanostructures. Through a combination of Bi determination methods the compositional profile of the film is shown to be graded and inhomogeneous. Furthermore, the coherent and pure zincblende phase property of the film is detailed. Optical characterisation of features on the sample surface is carried out using polarised micro-Raman and micro-photoluminescence spectroscopies. The important light producing properties of the surface nanostructures are investigated through pump intensity-dependent micro-PL measurements, whereby relatively large local inhomogeneities are revealed to exist on the epitaxial surface for important optical parameters. We conclude that such surface effects must be considered when designing and fabricating optical devices based on GaAsBi alloys.

Direct two-photon absorption induced emission of MBE grown undoped InAs/GaAs quantum dots (QDs) is investigated by power dependent photoluminescence and two-photon photoluminescence excitation study with excitation near the QDs half-bandgap.