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We report here our observance of superconductivity in compounds derived from the quaternary intermetallic superconductor YNi2B2C by partial substitutions for Ni. Other 3d transition metals T Î {Ti, V, Cr, Mn, Fe, Co, Cu, Zn} were used in replacement fractions x = 0.05 and x = 0.10. AC magnetic susceptibility cAC showed all except T = Zn had the characteristic diamagnetic response seen in superconductors. DC SQUID magnetometry on several samples confirmed type II superconducting behavior. X-ray diffraction showed a crystal structure similar to the parent compound for all but Zn. Some of the x = 0.10 compounds appeared to have minor secondary phases present despite annealing.

Exciton dynamics in a GaAsSb/GaAs quantum well (QW) heterostructure were investigated via both steady state and transient photoluminescence. The measurements at 10 K demonstrated the coexistence of localized excitons (LEs) and free excitons (FEs), while a blue-shift resulting from increased excitation intensity indicated their spatially indirect transition (IT) characteristics due to the type-II band alignment. With increasing temperature from 10 K, the LEs and FEs redistribute, with the LEs becoming less intense at relatively higher temperature. With increasing temperature to above 80 K, electrons in GaAs are able to overcome the small band offset to enter inside GaAsSb and recombine with holes; thus, a spatially direct transition (DT) appeared. Hence, we are able to reveal complex carrier recombination dynamics for the GaAsSb/GaAs QW heterostructure, in which the “S” shape behavior is generated not only by the carrier localization but also by the transformation from IT to DT with elevated temperature.

Strain engineering as one of the most powerful techniques for tuning optical and electronic properties of Ill-nitrides requires reliable methods for strain investigation. In this work, we reveal, that the linear model based on the experimental data limited to within a small range of biaxial strains (0.2%), which is widely used for the non-destructive Raman study of strain with nanometer-scale spatial resolution is not valid for the binary wurtzite-structure group-III nitrides GaN and AlN. Importantly, we found that the discrepancy between the experimental values of strain and those calculated via Raman spectroscopy increases as the strain in both GaN and AlN increases. Herein, a new model has been developed to describe the strain-induced Raman frequency shift in GaN and AlN for a wide range of biaxial strains (up to 2.5%). Finally, we proposed a new approach to correlate the Raman frequency shift and strain, which is based on the lattice coherency in the epitaxial layers of superlattice structures and can be used for a wide range of materials.Supplementary material (Table S1: Values of bulk phonon deformation potentials and elastic constants for GaN and AlN from each reference used in Table 1, Fig. S1: Lattice parameters of SL layers using Eq. (8), and Fig. S2: Raman mapping using Eq. (7)) is available in the online version of this article at 10.1007/s12274-021-3855-4.

We have designed graded InGaN quantum well (QW) structures with the In composition increasing then decreasing in a zigzag pattern. Through polarization doping, this naturally creates a p–n junction. Separate structures are designed by varying the maximum In composition but maintaining a constant QW thickness. This is both in order to test the limits of the molecular beam epitaxy growth control in terms of the deposition source ramping rates and to determine the limits of the maximum In composition within a narrow QW. The composition, x, of InxGa1−xN is varied for all structures starting from a minimum of xmin = ∼ 3%, and increasing to different maximum compositions, xmax, then finally decreasing back to ∼ 3%. The samples are characterized for their structural and luminescent properties. The results of the photoluminescence studies on samples with xmax ranging up to 35% demonstrate broadband emission covering wavelengths between 380 nm and 700 nm. Additionally, although the general emission of structures with increasing xmax shifts to lower energy, the observed luminescence is comprised of several individual peaks which are currently being investigated as to their particular origin.

The optical properties of periodic graded GaN/InGaN are studied. We have designed graded InGaN quantum well (QW) structures with the indium composition increasing then decreasing in a zigzag pattern. Through polarization doping, this naturally creates alternating p-type and n-type regions. Separate structures are designed by varying the number of repeating periods (1 to 3), while maintaining constant overall structure thicknesses. Calculation of the transition probabilities and the electron and hole wave-functions between the conduction band and the valence band reveals a complex energy structure which predicts the photoluminescence peaks for band to band transitions.

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.

Plastic strain relaxation in epitaxial layers is one of the crucial factors that limits the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consist...

The performances of various configurations of InGaN solar cells are compared using nextnano software. Here we compare a flat base graded wall GaN/InGaN structure, with an InxGa1-xN well with sharp GaN contact layers, and an InxGa1-xN structure with InxGa1-xN contact layers, i.e. a homojunction. The doping in the graded structures are the result of polarization doping at each edge (10 nm from each side) due to the graded structure, while the well structures are intentionally doped at each edge (10 nm from each side) equal to the doping concentration in the graded structure. The solar cells are characterized by their open-circuit voltage, V_oc, short circuit current, I_sc, solar efficiency, and energy band diagram. The results indicate that an increase in I_sc and efficiency results from increasing both the fixed and the maximum indium compositions, while the V_oc decreases. The maximum efficiency is obtained for the InGaN well with 60% In., Comment: 14 pages, 12 figures

The In(Ga)As/GaAs surface quantum dots (SQDs) have become appealing recently due to the special surface sensitivity property and consequently the advantage in developing sensors for humidity detection. This research reveals that the InGaAs/GaAs single-layer SQDs exhibit carrier separation due to Fermi level pinning, where electrons are pinned at surface but holes are confined inside the SQDs. Thus, photoluminescence (PL) features corresponding to carrier indirect transition are observed through a prominent blue-shift of ∼ 31 meV for the PL band that obeys a cube root power law over four orders of magnitude change in excitation power. The indirect transition of these SQDs is further characterized through time-resolved PL studies showing a biexponential decay with a relatively elongated carrier lifetime of ∼1.35 ns. This is the first time that a concept of type-II characteristic is proposed for the InGaAs SQDs, which will help to optimize the design and working principles for developing sensors with surface-sensitive InGaAs SQDs.

Self-assembled quantum dots grown by molecular beam epitaxy have been a hotbed for various fundamental research and device applications over the past decades. Among them, InAs/GaAs quantum dots have shown great potential for applications in quantum information, quantum computing, infrared photodetection, etc. Though intensively studied, some of the optical nonlinear properties of InAs/GaAs quantum dots, specifically the associated two-photon absorption of the wetting and barrier layers, have not been investigated yet. Here we report a study of the photoluminescence of these dots by using direct two-photon excitation. The quadratic power law dependence of the photoluminescence intensity, together with the ground-state resonant peak of quantum dots appearing in the photoluminescence excitation spectrum, unambiguously confirms the occurrence of the direct two-photon absorption in the dots. A three-level rate equation model is proposed to describe the photogenerated carrier dynamics in the quantum dot-wetting layer-GaAs system. Moreover, higher-order power law dependence of photoluminescence intensity is observed on both the GaAs substrate and the wetting layer by two-photon excitation, which is accounted for by a model involving the third-harmonic generation at the sample interface. Our results open a door for understanding the optical nonlinear effects associated with this fundamentally and technologically important platform.

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.

Carbon nanofilms are easier to integrate in electronic devices than their two-dimensional counterparts. With proper engineering, they can offer similar optical and electrical properties without any alteration because of material transfer effects. In the current research, amorphous carbon nanofilms with thicknesses of 2, 5 and 20 nm were prepared by electron beam evaporation onto glass substrates. The surface morphology, structural and optical properties were analyzed. Through ellipsometric analysis, the linear dielectric functions were quantified. The results confirm the presence of multiphase amorphous carbon structures in the films with different electronic hybridization. The 2 nm films which had the highest sp2/sp3 ratio exhibited a crossover wavelength at 397 nm related to epsilon near zero localization. The third-order nonlinear behavior close to this wavelength in all samples showed maximum response. Details and discussion of the preformed characterization and relation to potential applications are presented.

Carrier dynamics including carrier relaxation and tunneling within a coupled InAs quantum dot (QD) – In0.15Ga0.85As quantum well (QW) hybrid nanostructure are investigated using photoluminescence (PL) spectroscopy. This coupled hybrid nanostructure shows a single PL peak from the QD emission at low excitation intensity and a band filling behavior is observed as the excitation intensity increases, suggesting that there exists a channel to capture carriers from the QW to the QDs. Time resolved PL (TRPL) measurements extract a carrier tunneling time of 103.7 ps, which is only one third of the theoretical prediction. A double-channel resonant carrier tunneling mechanism from the QW to the wetting layer and to the fifth excited state of the QDs and then carrier relaxation into lower discrete QD energy states is proposed to explain this fast carrier tunneling. The double-channel resonant carrier tunneling mechanism is qualitatively supported through the analysis of the excitation-dependent PL spectra as well as the PL excitation spectra. These results enrich our understanding of carrier dynamics in coupled QD and QW hybrid structures.

GaN/Al0.20Ga0.80N/GaN heterostructures were grown by molecular beam epitaxy and fabricated into micro-Hall effect sensors for the purpose of simultaneous current and temperature detection. The devices were characterized over a temperature range of −183 °C to 252 °C and were determined to be linearly dependent on magnetic field and temperature throughout. The high room temperature mobility of 2000 cm2/Vs allowed for a very high magnetic field sensitivity of 113 VA−1T−1, which only decreased to 80 VA−1T−1 at 252 °C. The ability to measure temperature while at the same time measure the magnitude of the B-field, and thus current in a nearby line is demonstrated. A method of decoupling temperature and current signatures is also shown together with a simple method of offset voltage understanding and removal.

We experimentally demonstrate that the conductivity of graded AlxGa1–xN increases as a function of the magnitude of the Al concentration gradient (%Al/nm) due to polarization doping effects, without the use of impurity dopants. Using three up/down-graded AlxGa1–xN nanolayers with Al gradients ranging from ∼0.16 to ∼0.28%Al/nm combined in one structure, the effects of polarization engineering for localized electric fields and current transport were investigated. Cross-sectional Kelvin probe force microscopy and conductive atomic force microscopy were used to directly probe the electrical properties of the films with spatial resolution along the thickness of the growth. The experimental profiles of the built-in electric fields and the spreading current found in the graded layers are shown to be consistent with simulations of the field distribution as well as of the electron and hole densities. Finally, it was directly observed that for gradients less than 0.28%Al/nm the native n-type donors still limit pola...

Graded InGaN structures have been designed by increasing the indium composition from 3% to a maximum value then back to 3%. This results in a Zig-Zag quantum well (QW) structure with a composition grading and subsequent polarization doping, which forms a p-n junction. Separate structures are designed by varying the maximum In composition but maintaining a constant QW thickness. This is both in order to test the limits of the molecular beam epitaxy growth control in terms of the deposition source ramping rates and to determine the limits of the maximum In composition within a narrow QW. The results indicate that by increasing the maximum indium composition, the overall emission, while very broad, shifts to lower energies. The broadband emission covers wavelengths between 360 and 700 nm. Simulations identify the lowest energy, band-to-band transition for fully strained structures with a noticeable shift resulting from partial relaxation in samples with higher indium content. This type of novel polarization doped structure has useful applications in optoelectronic devices; therefore the presented understanding of its optical transitions will be beneficial to their design and implementation.

In this research, the nonlinear optical properties of Ni nano-films were investigated in the cw regime. Metallic films with thicknesses of 4, 8 and 16 nm were fabricated at room temperature by thermal evaporation. The film's nonlinear optical properties were determined using the z-scan technique pumped at 650 nm. The films showed saturable absorber behavior which became stronger with the film's thickness. However, this behavior was not observed when the films were irradiated at 405 nm. A model based on the allowed density of states in the fabricated films is adopted to explain the dependence of the saturable absorber on the irradiation wavelength. Through the mechanistic discernments of the model, capability of controlling nonlinear optical limiting by light is discussed.

The effect of different quantum structures in the intrinsic region of a pin junction solar cell (SC) on the optical and electrical properties have been investigated. SCs with different quantum structures, such as, Stranski-Krastanov (SK) quantum dots (QDs), quantum well (QW), submonolayer (SML) QDs (0.25 ML, 0.5 ML and 0.75 ML) and a quasi-monolayer (1 ML) InAs stack, were fabricated while keeping the total InAs content the same in all SCs. In a comparison of performance, the SML-QD sample delivered superior performance (Almost 23% relative efficiency improvement compared to reference SC) compared to the other devices. Moreover, different coverages of SML InAs have been tested for optimum performance improvement of solar cell and near 0.25 ML InAs deposition was found best for solar cell application. These findings present a promising alternative to SK-QDs as intermediate band in photovoltaic applications.

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.

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/GaAs 1−x Bi x /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.

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.

Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n+/n0/n+-GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

A magnetophotoluminescence study of the carrier transfer with hybrid InAs/GaAs-quantum-dot-InGaAs-quantum-well structures is carried out where we observe an unusual 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 quantum-well (QW) PL intensity is observed to increase at the expense of a decrease in the quantum-dot (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., The authors gratefully acknowledge the financial support of the following agencies: National Science Foundation of the U.S. (Grants No. DMR1008107 and No. DMR-1108285),CSIC grant ICOOP-2017-COOPB20320, MINEICO grant EUIN2017- 88844, FAPESP (grants # 2013/18719-1, 2014/07375- 2, 2014/19142-2, 2018/01914-0), CNPq(164765/2018-2) and CAPES (Finance Code 001).

The GaSb quantum dots (QDs) with type II band alignment have attracted great attention recently. They are predicted to be optimizing active region materials for achieving high efficient intermediate-band solar cells and for obtaining ultra-long storage time for memory cells. In this research, GaSb QDs sandwiched inside InAlAs matrix lattice-matched to InP (001) substrate have been obtained via droplet epitaxy. The droplet epitaxy enable us to achieve low density (~2.6 x 10^9/cm^2) and large size (average height ~6.5nm) for the QDs while the lattice mismatch between the GaSb and InAlAs matrix is only ~4%. PL measurements reveal a type-II band alignment for these GaSb/InAlAs/InP QDs. The PL peak energy of QDs shows a blue-shift of >100 meV when the laser intensity increases by six orders of magnitude. Time-resolved PL measurements further confirm the type-II band alignment for the QDs by showing a maximum carrier lifetime of ~4.5 ns. The abnormal dependence of peak energy of QD PL band on the temperature in together with the special PL decay curve indicate that these GaSb/InAlAs QDs likely have different physics mechanism from common GaSb/GaAs type-II QDs. This study provide useful information for understanding the band structure and carrier dynamics of the GaSb/InAlAs QDs grown on InP surface.

Ionizing radiation has the potential to cause operational disruptions and destroy microelectronic devices. This paper introduces and demonstrates a method of hardening microelectronic devices for sustained use in applications where exposure to ionizing radiation exists. By incorporating quantum structures below active regions of devices, gettering of charges created by ionizing radiation becomes possible. The gettering of electrons and holes forces recombination of carriers, thus eliminating photocurrent surges and trap filling which would otherwise disrupt device operation. Experimental results discussed here show a reduction in photocurrent of over two orders of magnitude when utilizing energy band engineering to create quantum structures for charge gettering. In this work, a nitride-based high electron mobility two-dimensional electron gas demonstrates the method. However, the theory utilized pertains not only to nitride-based devices, but transfers to other materials as well.

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 ~2.5 times results in more pronounced {10–15} facets of InN nanostructures and decreasing of the residual electron concentration from ~5.8 · 1017 cm−3 to ~2.5 · 1017 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.

This work provides a review of commonly used approaches for fine manipulations with nanoobjects by means of scanning probe microscopes and describes an original alternative cost-effective nanomanipulation method. High precision manipulations are important for up-to-date technologies of nanoelectronic, molecular, hybrid and nanomechanical devices and sensor systems especially for the state of the art fundamental and applied researches. A new method to form nanoassemblies by using asymmetric nanoparticles fixed on the surface with the viscoelastic linker has been proposed, theoretically substantiated and experimentally realized. An original theoretical model has been proposed to describe the ordering process of the linked nanorods by means of the multipass interaction with an atomic force microscope (AFM) tip.In addition, an adjustment of the tip-surface interaction has been proposed and implemented which is independent of the AFM. This original approach is based on additional ultrasonic excitation of the surface. This also enabled us to control the degree binding of the nanoparticles with the substrate.With these techniques we were able to form sets of chains (more than 5-μm length) consisting of nanometer-sized (10x50 nm) gold nanorods (NRs) linked to the surface of gallium arsenide by an organic linker. It has been shown that the viscoelastic binding of asymmetric nanoparticles to the surface allows us to create linear assemblies of nanoobjects in just a few passes of the AFM probe.The proposed technique significantly increases manufacturability of nanomanipulations. Direct formation of nanostructures can significantly reduce the cost of their formation in comparison with modern conventional technological approaches, which in many cases may even have some fundamental limitations (in resolution, in materials used, etc.).

The influence of strain and barrier/well thickness ratio on recombination processes in multi-quantum well (MQW) Al0.1Ga0.9N/GaN structures was investigated using X-ray diffraction and Raman and photoluminescence spectroscopies. The deformation state of the wells and barriers was determined. In addition, the value of the polarization fields, the density of polarization charges, and the positions of energy levels for optical transitions within the quantum wells were calculated. It was established that compressive strain in the buffer layer as well as in the layers of the MQWs with respect to the buffer layer lead to the piezoelectric fields having equal sign in the well and the barrier. As a result, the recombination of donor–acceptor pairs dominates over transitions between electron and hole states in the quantum well.

Group-IV alloys of Ge and/or Si with Sn are challenging to prepare due to the low solubility of Sn in both of these elements. Herein, we describe a remote plasma-enhanced chemical vapor deposition (RPECVD) system designed to synthesize such group-IV alloys. Thin films of Ge, Ge1−ySiy, Ge1−xSnx, and Ge1−x−ySiySnx were deposited in the range of 280−410 °C on Si (001) substrates utilizing a remote He plasma with downstream injected mixtures of SnCl4, SiH4, and/or GeH4 precursors. The composition and structural properties of these RPECVD films were characterized with x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. They were found to be crystalline, oriented with the substrate, and nearly relaxed due to the formation of an ∼5 nm thick interface layer with a high density of edge dislocations and stacking faults.

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.

GaSb quantum dots (QDs) have been grown by droplet epitaxy within InAlAs barrier layers on an InP (001) substrate. The droplet growth mode facilitates a larger size (average height ∼4.5 nm) and a lower density (∼6.3 × 109 cm-2) for the QDs than would be expected for the 4% lattice mismatch between GaSb and InAlAs. A type-II band alignment between the GaSb QDs and the InAlAs barriers is revealed by photoluminescence (PL) through a prominent blue-shift of ∼0.11 eV resulting from a six orders of magnitude increase in excitation power. Further confirmation of the type-II nature of these QDs is found through time-resolved PL studies showing a biexponential decay with a long carrier lifetime of ∼10.9 ns. These observations reveal new information for understanding the formation and properties of GaSb/InAlAs/InP QDs, which may be an optimum system for the development of both efficient memory cells and photovoltaic devices.