Gregory Salamo

• University of Arkansas at Fayetteville

Photonic integrated circuits (PICs) have been acknowledged as the promising platforms for the applications in data communication, Lidar in autonomous driving vehicles, innovative sensor technology, etc. Since the demonstration of optical components individually, integration of both electronics and photonics for functional devices on a common platfo...

This research provides a flexible approach to manipulate formation of InGaAs nanostructures on the GaAs (100) surface by varying arsenic (As4) beam equivalent pressure (BEP). By selecting the As4/(In+Ga) BEP ratio to be 4, 8, 20, 50 and 100, we were able to obtain different quantum structures from quantum well (QW) to quantum dots (QDs), then to sp...

Sapphire has various applications in photonics due to its broadband transparency, high-contrast index, and chemical and physical stability. Photonics integration on the sapphire platform has been proposed, along with potentially high-performance lasers made of group III–V materials. In parallel with developing active devices for photonics integrati...

We report on the growth of high-quality GaAs semiconductor materials on an AlAs/sapphire substrate by molecular beam epitaxy. The growth of GaAs on sapphire centers on a new single-step growth technique that produces higher-quality material than a previously reported multi-step growth method. Omega-2theta scans confirmed the GaAs (111) orientation....

The study aimed to investigate the underlying physics limiting the temperature stability and performance of non-surface passivated Al0.34Ga0.66N/GaN Hall effect sensors, including contacts, under atmospheric conditions. The results obtained from analyzing the microstructural evolution in the Al0.34Ga0.66N/GaN Hall sensor heterostructure were found...

The impact of the growth orientation on spin dynamics in GaAs/AlGaAs quantum wells (QWs) is explored through magnetophotoluminescence measurements. Samples grown on both (100) and (311)A GaAs surfaces exhibit intensity oscillations at high magnetic fields, characteristic of magnetoabsorption arising from interband transitions between Landau levels...

The development of all-group IV GeSn materials on Si substrates is of interest for monolithic midwave infrared (MWIR) silicon photonics. Despite their great potential, the growth of high crystalline quality materials is still challenging. The conventional growth of GeSn films on Si displays high densities of dislocations and, hence, large dark curr...

High-quality InN has significant opportunities for exciting and impactful electronic and photonic applications. These applications rely on growth techniques that produce high-quality InN thin films. To achieve the fabrication of InN semiconductor thin films with a low density of misfit and threading dislocations, we report on a growth technique tha...

Atomic short-range order (SRO) in direct-bandgap GeSn for infrared photonics has recently attracted attention due to its notable impact on band structures. However, the SRO in GeSn thin films grown by different methods have hardly been compared. This paper compares SRO in GeSn thin films of similar compositions grown by molecular beam epitaxy (MBE)...

The growth of high-composition GeSn films in the future will likely be guided by algorithms. In this study, we show how a logarithmic-based algorithm can be used to obtain high-quality GeSn compositions up to 16% on GaAs (001) substrates via molecular beam epitaxy. Herein, we use composition targeting and logarithmic Sn cell temperature control to...

SiC is an indirect bandgap semiconductor with material properties ideal for power electronics but not so much as an optical emitter. Meanwhile, gallium arsenide (GaAs) is a material known for high-performance optical devices due to its direct bandgap and carrier lifetime. Integrating GaAs with silicon carbide (SiC) can result in the best of both ma...

We report for the first time on an aluminum nitride/gallium nitride (AlN/GaN) heterostructure as a microscale Hall effect sensor for current sensing applications in extreme environments. The AlN/GaN devices demonstrated high signal linearity as a function of the magnetic field across a temperature range from $-$ 193 $^{\circ}$ C to 407 $^{\cir...

In the manufacture of semiconductor devices, cracking of heterostructures has been recognized as a major obstacle for their post-growth processing. In this work, we explore cracked GaN/AlN multi-quantum wells (MQWs) to study the influence of pressure on the recombination energy of the photoluminescence (PL) from the polar GaN QWs. We grow GaN/AlN M...

A DC to 25 MHz readout interface design for Hall-effect sensors is presented. The current sensing system is comprised of a high-bandwidth aluminum gallium nitride/gallium nitride (AlGaN/GaN) or aluminum gallium arsenide/gallium arsenide (AlGaAs/GaAs) Hall-effect sensor and an on-chip fast readout interface. The interface makes use of multi-signal p...

We have grown AlN/GaN/AlN heterostructures by molecular beam epitaxy and fabricated Hall sensors. In a comparison with fabricated AlGaN/AlN/GaN Hall sensors, we find that the AlN/GaN/AlN quantum well Hall sensors have higher sensitivity under constant current bias. In addition, the application of a gate voltage shows a further increase in the Hall...

Germanium tin (GeSn) is a tuneable narrow bandgap material, which has shown remarkable promise for the industry of near- and mid-infrared technologies for high efficiency photodetectors and laser devices. Its synthesis is challenged by the lattice mismatch between the GeSn alloy and the substrate on which it is grown, sensitively affecting its crys...

Germanium films were grown on c-plane sapphire with a 10 nm AlAs buffer layer using molecular beam epitaxy. The effects of Ge film thickness on the surface morphology and crystal structure were investigated using ex situ characterization techniques. The nucleation of Ge proceeds by forming (111) oriented three-dimensional islands with two rotationa...

We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h unde...

Germanium films were grown on c-plane sapphire with a 10 nm AlAs buffer layer using molecular beam epitaxy. The effects of Ge film thickness on the surface morphology and crystal structure were investigated by ex-situ characterization techniques. The nucleation of Ge proceeds by forming (111) oriented three-dimensional islands with two rotational t...

High-quality GaAs on c-plane sapphire has been achieved by employing a two-step growth technique, multiple annealing, and an AlAs nucleation layer using molecular beam epitaxy (MBE). The effect of growth parameters, namely growth temperature, As2 flux, and low-temperature layer growth temperature (LTLGT) in two-step growth have been investigated. I...

In this work, we study the thermal evolution of the optical and electrical features of an InN thin film. By correlating photoluminescence (PL) and Hall effect results, we determine the appropriate values of the correlation parameter to be used in the empirical power law that associates the electron concentration with the linewidth of the PL spectru...

This work investigates the temperature dependence of the performance of In(Ga)As-based solar cells made from sub-monolayer (SML) quantum dots (QDs), quantum wells (QWs), and Stranski-Krastanov QDs (SK-QDs). Welldefined sub-bandgap peaks are observed in external quantum efficiency (EQE) spectra for all samples. Apparently, changes in minority carrie...

We have used temperature-dependent photoconductivity (PC) with different excitation wavelengths and intensities to study the photoexcited charge-carrier transport within GeSn/Ge/Si heterostructures. The evolution of the PC spectra with temperature was analyzed between 10 and 200 K. These strained GeSn films were grown with high enough Sn content su...

Elastic strain engineering in the GeSn bandgap structure is an attractive area for designing novel material properties. The linear interpolation of the elastic constants of Ge and Sn is commonly used to estimate their respective values for Ge1−xSnx alloys. This work reveals that Young's modulus of Ge1−xSnx epitaxial layers has a non-monotonic depen...

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 tr...

Monolithic integration of infrared photodetectors on a silicon platform is a promising solution for the development of scalable and affordable photodetectors and infrared focal plane arrays. We report on integration of submonolayer quantum dot quantum cascade detectors (SML QD QCDs) on Si substrates via direct growth. Threading dislocation density...

Group III-V materials on sapphire substrate opens a new avenue for photonics integrated circuits. GaAs/AlGaAs straight waveguides on sapphire substrate were numerically studied. The propagation loss, single-mode, and multi-mode operation conditions were reported.

InAs(Sb)/GaAs self-assembled quantum dots (QDs) were grown by molecular beam epitaxy though incorporating Sb into InAs with increased beam equivalent pressure ratio, x = Sb2/(Sb2+As2), of x = 0, 0.15, 0.25, and 0.5. From photoluminescence measurements, we observed a transition of the band alignment from type-I for the InAs QDs to type-II for InAsSb...

Recent studies of SiGeSn materials and optoelectronic devices hold great promise for photonics integrated circuits (PICs) on Si platform featuring scalable, cost-effective, and power-efficient. Thanks to the breakthrough of low temperature material growth techniques, device-quality level materials have been grown, following by the demonstration of...

The formation of GeSn nanostructures catalyzed by Sn surface droplets during the growth of Ge1-xSnx/Ge/Si(001) heterostructures provide a promising strategy for the growth of high-quality Sn-containing group-IV alloys. The droplet formation is favored by Sn segregation at dislocation cores and diffusion of Sn towards the sample surface. Subsequent...

GeSn-based quantum wells are of great interests for the development of all-group-IV optoelectronic devices such as lasers. Using a GeSn buffer and SiGeSn barrier has been studied with the aim of obtaining a direct bandgap well and increasing the carrier confinement. However, the carrier collection efficiency with such a configuration remains unsati...

Exciton localization has been investigated via photoluminescence (PL) measurements for a 50 nm InGaAs/InAlAs wide quantum well (QW) lattice-matched to an InP substrate. Discrete QW emission bands from both localized exciton (LE) recombination and free exciton (FE) recombination were observed, demonstrating modified state filling with increasing pum...

Stacking growth of the InGaAs quantum dots (QDs) on top of a carrier injection layer is a very useful strategy to develop QD devices. This research aims to study the carrier injection effect in hybrid structures with a layer of In0.4Ga0.6As surface quantum dots (SQDs), coupled to an injection layer of either one layer of In0.4Ga0.6As buried QDs (BQ...

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 and 50 K, the scattering with acoustic phonons and short-range interac...

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 su...

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-destruc...

This paper discusses the combined effects of optical excitation power, interface roughness, lattice temperature, and applied magnetic fields on the spin-coherence of excitonic states in GaAs/AlGaAs multiple quantum wells. For low optical powers, at lattice temperatures between 4 K and 50 K, the scattering with acoustic phonons and short-range inter...

A nondestructive approach is described that is applicable for studying the In-segregation phenomena in ultra-thin In(Ga)As/GaAs nanostructures grown by molecular beam epitaxy. The proposed method utilizes only the experimental photoluminescence (PL) spectroscopy data and the effective bandgap simulation of specially designed ultra-thin In(Ga)As/GaA...

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 strain relaxation, depth profiles of composition and density of dislocations in GeSn epilayers were studied by using the x-ray diffraction. Regions with uniform and graded composition, different levels of strain relaxation, and dislocation density were found in the GeSn layers grown at fixed growth conditions. At the initial stage of growth, th...

The effects of lattice misfit strain in epitaxial GeSn/Ge/Si(001) heterostructures on Sn incorporation, misfit dislocations (MDs), and the critical thickness were investigated using high-resolution x-ray diffraction. By performing a simulation of the x-ray reciprocal space maps measured in the vicinity of an asymmetrical reflection, we determined t...

The strain distribution in compositionally graded AlGaN planar structures, pillars, and nanowires (NWs) has been studied by three-dimensional (3D) strain calculations based on a numerical finite element method (FEM) and X-ray diffraction reciprocal space mapping. First, new fitting analyses of the reciprocal space maps (RSMs) are demonstrated to ev...

Lysenin is a pore-forming toxin, which self-inserts open channels into sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. Here, we have employed a novel combination of experimental and computational techniques to exam...

The near-bandgap optical properties of Ge1-xSnx alloys were characterized by photovoltage spectroscopy and spectral ellipsometry measurements. Contributions of Urbach tailing as well as direct and indirect optical transitions were observed. The compositional dependence of direct bandgaps of strained GeSn films grown on a Ge buffered Si substrate wa...

Photoelectrochemical production of hydrogen by using sunlight to split water offers a sustainable approach for clean energy generation. III-V Semiconductors have shown the highest efficiencies for photoelectrochemical water splitting but the prohibitive cost of commercial single-crystalline GaP wafers limit practical use and large-scale application...

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 observ...

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...

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 t...

InGaAs quantum wire (QWr) intermediate-band solar cell–based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current–voltage (I–V) and capacitance–voltage (C-V) techniques, were found to change with temperature over a wide range of 20–340 K. The electr...

InGaAs quantum wire (QWr) intermediate-band solar cell–based nanostructures grown by molecular beam epitaxy are studied. The electrical and interface properties of these solar cell devices, as determined by current–voltage (I–V) and capacitance–voltage (C-V) techniques, were found to change with temperature over a wide range of 20–340 K. The electr...

Carrier transfer in vertically-coupled InAs/GaAs quantum dot (QD) pairs is investigated. Photoluminescence (PL) and PL excitation spectra measured at low temperature indicate that the PL peak intensity ratio between the emission from the two sets of QDs—i.e., the relative population of carriers between the two layers of QDs—changes with increasing...

The enhancement of light from semiconductors due to surface plasmons coupled resonantly to its emission is limited because of dissipation in the metal and is also restricted by the dielectric characteristics and homogeneity of the metal–semiconductor interface. We report a new mechanism based on electrostatic interactions of carriers and their imag...

Structures with one-dimensional quantum objects in intermediate band are promising for their application in solar cells and photodetectors. We present analysis of dark current-voltage characteristics, photo-voltage decay and photo-voltage spectra for this structures in comparison with reference GaAs based structures. It has been shown that InGaAs q...

We uncover the underlying physics that explains the energy shifts of discrete states of individual InAs lateral quantum dot molecules (LQDMs) as a function of magnetic fields applied in the Faraday geometry. We observe that ground states of the LQDM exhibit a diamagnetic shift while excited states exhibit a paramagnetic shift. We explain the physic...

The interplay between structural properties and charge transfer in self-assembled quantum ring (QR) chains grown by molecular beam epitaxy on top of an InGaAs/GaAs quantum dot (QD) superlattice template is analyzed and characterized. The QDs and QRs are vertically stacked and laterally coupled as well as aligned within each layer due to the strain...

The authors report 1.3-mu m InAs/GaAs quantum-dot (QD) lasers monolithically grown on a Si substrate by optimising the dislocation filter layers (DFLs). InAlAs/GaAs strained layer superlattices (SLSs) have been presented as DFLs in this study. A distinct improvement in the InAs/GaAs QDs was observed when using InAlAs/GaAs SLSs because of the effect...

In present study, the intense sensitized three photon near-infrared quantum cutting luminescence of Tm³⁺ ion activator in Tm³⁺Bi³⁺:YNbO4 powder phosphor is reported. It is induced both by [{¹G4→³H4, ³H6→³H5} or {¹G4→³H5, ³H6→³H4}] and {³H4→³F4, ³H6→³F4} cross-energy transfer. We found that the 1820.0 nm ³F4→³H6 luminescence intensity of Tm0.08Bi0.0...

Here, we demonstrate X-ray fitting through kinematical simulations of the intensity profiles of symmetric reflections for epitaxial compositionally graded layers of AlGaN grown by molecular beam epitaxy pseudomorphically on [0001]-oriented GaN substrates. These detailed simulations depict obvious differences between changes in thickness, maximum co...

The in-plane photoconductivity and photoluminescence are investigated in quantum dot-chain InGaAs/GaAs heterostructures. Different photoconductivity transients resulting from spectrally selecting photoexcitation of InGaAs QDs, GaAs spacers, or EL2 centers were observed. Persistent photoconductivity was observed at 80 K after excitation of electron-...

A high-performance 1.3 μm InAs/GaAs quantum-dot laser directly grown on Si substrates has been achieved by using InAlAs/GaAs strained-layer superlattice serving as dislocation filter layers (DFLs). The Si-based laser achieves lasing operation up to 111°C with a threshold current density of 200 A/cm2 and an output power exceeding 100 mW at room temp...

Detailed studies of solar cell efficiency as a function of temperature were performed for quantum wire intermediate band solar cells grown on the (311)A plane. A remotely doped one-dimensional intermediate band made of self-assembled In0.4Ga0.6As quantum wires was compared to an undoped intermediate band and a reference p-i-n GaAs sample. These stu...

Strain-based band engineering in quantum dots and dashes has been predominantly limited to compressively strained systems. However, tensile strain strongly reduces the bandgaps of nanostructures, enabling nanostructures to emit light at lower energies than they could under compressive strain. We demonstrate the self-assembled growth of dislocation-...

Building optoelectronic devices on a Si platform has been the engine behind the development of Si photonics. In particular, the integration of optical interconnects onto Si substrates allows the fabrication of complex optoelectronic circuits, potentially enabling chip-to-chip and system-to-system optical communications at greatly reduced cost and s...

A comprehensive microscopy analysis has been undertaken to study three-dimensional quantum dot (QD) ordering in multilayered In0.4Ga0.6As/GaAs structures grown with an As2 flux at different substrate temperatures. Atomic force microscopy, transmission electron microscopy, and photoluminescence measurements were employed to fully understand the form...

We report on the mechanism of strain-influenced quantum well (QW) thickness reduction in GaN/AlN short-period superlattices grown by plasma-assisted molecular beam epitaxy. Density functional theory was used to support the idea of a thermally activated exchange mechanism between Al adatoms and Ga surface atoms that is influenced by the strain state...

We report room-temperature Raman scattering studies of nominally undoped (100) GaAs1−xBi x epitaxial layers exhibiting Bi-induced (p-type) longitudinal-optical-plasmon-coupled (LOPC) modes for 0.018 ≤ x ≤ 0.048. Redshifts in the GaAs-like optical modes due to alloying are evaluated and are paralleled by strong damping of the LOPC. The relative inte...

We compare InAlAs/GaAs and InGaAs/GaAs strained-layer superlattices (SLSs) as dislocation filter layers for 1.3-μm InAs/GaAs quantum-dot laser structures directly grown on Si substrates. InAlAs/GaAs SLSs are found to be more effective than InGaAs/GaAs SLSs in blocking the propagation of threading dislocations generated at the interface between the...

Materials with one-dimensional quantum structures are promising for their application in solar cells. The photo-voltage generation of these structures is caused by spatial separation of electron-hole pairs by a built-in electric field in the GaAs p-i-n junction. The InGaAs/GaAs sample shows a significantly higher photo-voltage in the spectral range...

The realization of high efficiency quantum dot intermediate band solar cells is challenging due to the thermally activated charge escaping at high temperatures. The enhancement in short circuit current of quantum dot solar cells is largely undermined by the voltage loss. In this paper, InAs/GaAs quantum dot solar cells with direct Si doping in the...

Strong optical anisotropy is observed in the emission from a GaAs1−xBix (x ∼ 0.04) quantum well grown by low temperature molecular beam epitaxy on (001) GaAs by means of low temperature magneto-photoluminescence (MPL) taken at 2 K in Faraday geometry for magnetic fields, B, up to 10 T. A significant diamagnetic shift (∼2.5 meV) develops for magneti...

The effect of rapid thermal annealing on the optical and structural properties of GaAsBi/GaAs quantum wells (QWs) is investigated. The photoluminescence (PL) spectra of the samples are measured at 80 K and room temperature before and after rapid thermal annealing, to ascertain any improvement in the optical quality of the material. The impact of an...

Self-assembled InGaAs quantum dots (QDs) were fabricated inside a planar microcavity with two vertical cavity modes. This allowed us to excite the QDs coupled to one of the vertical cavity modes through two propagating cavity modes to study their down- and up-converted photoluminescence (PL). The up-converted PL increased continuously with the incr...

Scanning confocal micro-Raman and PL spectroscopy, Kelvin probe force microscopy (KPFM) and electrostatic force gradient microscopy (EFGM) were applied to study the concentration profiles of free carriers by scanning the cleaved edge along the growth direction of vertical n+/n0/n+-GaN Gunn-diode structure. The vertical frequency profile of the L– b...

Fabrication of advanced artificial nanomaterials is a long‐term pursuit to fulfill the promises of nanomaterials. In the last ten years, Droplet Epitaxy has been emerging as a versatile fabrication method for various complex nanomaterials, but there is a lack of growth protocol to control the growth vertically. Here we report a vertically correlate...

Creating and manipulating materials at the nanoscale with controllable size, shape and nucleation site is an important task to meet the urgent demands for quantum structures with designed properties. In the last ten years, droplet epitaxy has been emerging as a versatile fabrication method for various complex nanostructures, such as quantum dots, q...