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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Role of dislocation scattering on electron mobility in coalescent epitaxial lateral overgrowth layers of InP

In order to clarify the effects of dislocation scattering on electron transport properties, temperature dependent (15-300 K) Hall-effect measurements were applied to the dislocated coalescent and dislocation-free non-coalescent ELO layers of InP prepared by the liquid phase epitaxy. The coalescent ELO layers contain a large number of dislocations, and the non-coalescent ELO layers are dislocation-free. Taking into account, the various electron scattering mechanisms in compound semiconductors, the temperature dependences of electron mobility were analyzed. It is shown that the dislocation scattering based on the charged dislocation line model is dominant transport mechanism in the dislocated coalescent ELO layers at low temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Room-temperature mid-infrared “M”-type GaAsSb/InGaAs quantum well lasers on InP substrate

We have demonstrated experimentally the InP-based “M”-type GaAsSb/InGaAs quantum-well (QW) laser lasing at 2.41 μm at room temperature by optical pumping. The threshold power density per QW and extracted internal loss were about 234 W/cm{sup 2} and 20.5 cm{sup −1}, respectively. The temperature-dependent photoluminescence (PL) and lasing spectra revealed interesting characteristics for this type of lasers. Two distinct regions in the temperature dependent threshold behavior were observed and the transition temperature was found to coincide with the cross over point of the PL and lasing emission peaks. The current-voltage characteristic of “M”-type QW laser was superior to the inverse “W”-type one due to its thinner barrier for holes. Further improvement of the “M”-type QW structure could lead to a cost-effective mid-infrared light source.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Materials properties and dislocation dynamics in InAsP compositionally graded buffers on InP substrates

The properties of InAs{sub x}P{sub 1−x} compositionally graded buffers grown by metal organic chemical vapor deposition are investigated. We report the effects of strain gradient (ε/thickness), growth temperature, and strain initiation sequence (gradual or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes increased dislocation densities (>10{sup 6}/cm{sup 2}) and tilt of the epi-layer (>0.1°). A method of abrupt strain initiation is proposed which can result in dislocation densities as low as 1.01 × 10{sup 5} cm{sup −2} for films graded from the InP lattice constant to InAs{sub 0.15}P{sub 0.85}. A model for a two-energy level dislocation nucleation system is proposed based on our results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effect of band offset on carrier transport and infrared detection in InP quantum dots/Si nano-heterojunction grown by metalorganic chemical vapor deposition technique

Epitaxy of III-V semiconductors on Si gets recent interest for next generation system on heterogeneous chip on wafer. The understanding of band offset is thus necessary for describing the charge transport phenomenon in these heterojunctions. In this work, x-ray photoemission spectroscopy has been used to determine the band offsets in a heterojunction made of InP quantum dots on Si. The valence and conduction band offset was found to be 0.12 eV and 0.35 eV, respectively, with a type-II band lineup. Deviation from theoretical prediction and previously published reports on quasi similar systems have been found and analyzed on the basis of the effect of strain, surface energy, shift in the electrostatic dipole and charge transfer at the interface. The carrier transport mechanisms along with different device parameters in the heterojunction have been studied for a temperature range of 180–300 K. This heterojunction is found to behave as an efficient infrared photodetector with an ON/OFF ratio of 21 at a reverse bias of 2 V. The corresponding rise and decay time was found to be 132 ms and 147 ms, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Volmer–Weber InAs quantum dot formation on InP (113)B substrates under the surfactant effect of Sb

We report on Sb surfactant growth of InAs nanostructures on GaAs{sub 0.51}Sb{sub 0.49} layers deposited on InP (001) and on (113)B oriented substrates. On the (001) orientation, the presence of Sb significantly favors the two-dimensional growth regime. Even after the deposition of 5 mono-layers of InAs, the epitaxial film remains flat and InAs/GaAs{sub 0.51}Sb{sub 0.49} type-II quantum wells are achieved. On (113)B substrates, same growth runs resulted in formation of high density InAs islands. Microscopic studies show that wetting layer is missing on (113)B substrates, and thus, a Volmer-Weber growth mode is concluded. These different behaviors are attributed to the surface energy changes induced by Sb atoms on surface.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Contactless electroreflectance and theoretical studies of band gap and spin-orbit splitting in InP{sub 1−x}Bi{sub x} dilute bismide with x ≤ 0.034

Contactless electroreflectance is applied to study the band gap (E{sub 0}) and spin-orbit splitting (Δ{sub SO}) in InP{sub 1−x}Bi{sub x} alloys with 0 < x ≤ 0.034. The E{sub 0} transition shifts to longer wavelengths very significantly (−83 meV/% Bi), while the E{sub 0} + Δ{sub SO} transition shifts very weakly (−13 meV/% Bi) with the rise of Bi concentration. These changes in energies of optical transitions are discussed in the context of the valence band anticrossing model and ab initio calculations. Shifts of E{sub 0} and E{sub 0} + Δ{sub SO} transitions, obtained within ab-initio calculations, are −106 and −20 meV per % Bi, respectively, which is in a good agreement with experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

MgSe/ZnSe/CdSe coupled quantum wells grown on InP substrate with intersubband absorption covering 1.55 μm

The authors report the observation of intersubband (ISB) transitions in the optical communication wavelength region in MgSe/ZnSe/CdSe coupled quantum wells (QWs). The coupled QWs were grown on InP substrates by molecular beam epitaxy. By inserting ZnSe layers to compensate the strain, samples with high structural quality were obtained, as indicated by well resolved satellite peaks in high-resolution x-ray diffraction. The observed ISB transition energies agree well with the calculated values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Photovoltaic conversion of visible spectrum by GaP capped InP quantum dots grown on Si (100) by metalorganic chemical vapor deposition

Growth of GaP capped strained InP quantum dots was carried out by metal organic chemical vapor deposition technique on Si (100) substrates to explore an alternative material system for photovoltaic conversion. Studies on reflectance spectroscopy show higher absorption of visible photons compared to scattering. Smooth and defect free interface provides low dark current with high rectification ratio. A solar cell made of five periods of quantum dots is found to provide a conversion efficiency of 4.18% with an open circuit voltage and short circuit current density of 0.52 V and 13.64 mA/cm{sup 2}, respectively, under AM 1.5 solar radiation.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Continuous wave vertical cavity surface emitting lasers at 2.5 μm with InP-based type-II quantum wells

A concept for electrically pumped vertical cavity surface emitting lasers (VCSEL) for emission wavelength beyond 2 μm is presented. This concept integrates type-II quantum wells into InP-based VCSELs with a buried tunnel junction as current aperture. The W-shaped quantum wells are based on the type-II band alignment between GaInAs and GaAsSb. The structure includes an epitaxial GaInAs/InP and an amorphous AlF{sub 3}/ZnS distributed Bragg reflector as bottom and top (outcoupling) mirror, respectively. Continuous-wave operation up to 10 °C at a wavelength of 2.49 μm and a peak output power of 400 μW at −18 °C has been achieved. Single-mode emission with a side-mode suppression ratio of 30 dB for mesa diameters up to 14 μm is presented. The long emission wavelength and current tunability over a wavelength range of more than 5 nm combined with its single-mode operation makes this device ideally suited for spectroscopy applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Quantum confinement of excitons in wurtzite InP nanowires

Exciton resonances are observed in photocurrent spectra of 80 nm wurtzite InP nanowire devices at low temperatures, which correspond to transitions between the A, B, and C valence bands and the lower conduction band. Photocurrent spectra for 30 nm WZ nanowires exhibit shifts of the exciton resonances to higher energy, which are consistent with finite element calculations of wavefunctions of the confined electrons and holes for the various bands.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Extended wavelength mid-infrared photoluminescence from type-I InAsN and InGaAsN dilute nitride quantum wells grown on InP

Extended wavelength photoluminescence emission within the technologically important 2–5 μm spectral range has been demonstrated from InAs{sub 1−x}N{sub x} and In{sub 1−y}Ga{sub y}As{sub 1−x}N{sub x} type I quantum wells grown onto InP. Samples containing N ∼ 1% and 2% exhibited 4 K photoluminescence emission at 2.0 and 2.7 μm, respectively. The emission wavelength was extended out to 2.9 μm (3.3 μm at 300 K) using a metamorphic buffer layer to accommodate the lattice mismatch. The quantum wells were grown by molecular beam epitaxy and found to be of a high structural perfection as evidenced in the high resolution x-ray diffraction measurements. The photoluminescence was more intense from the quantum wells grown on the metamorphic buffer layer and persisted up to room temperature. The mid-infrared emission spectra were analysed, and the observed transitions were found to be in good agreement with the calculated emission energies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Band offsets and electronic structures of interface between In{sub 0.5}Ga{sub 0.5}As and InP

III–V semiconductor interfacing with high-κ gate oxide is crucial for the high mobility metal-oxide-semiconductor field transistor device. With density functional theory calculations, we explored the band offsets and electronic structures of the In{sub 0.5}Ga{sub 0.5}As/InP interfaces with various interfacial bondings. Among six different bonding interfaces, we found that P-In(Ga) bonding interface showed the highest stability. Local density of states calculations was adopted to calculate the band offsets. Except for the metallic interface, we noticed that neither valence band offset nor conduction band offset depended on the interfacial bondings. For the most stable P-In(Ga) interface, we did not observe any gap states. Furthermore, we explored the P-In(Ga) interfaces with interfacial P-As exchange defects, which slightly modified the interface stability and the band offsets but did not produce any gap states. These findings provide solid evidence that InP could serve as a promising interfacial passivation layer between III–V material and high-κ oxide in the application of high mobility devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Optimizing the quality factor of InP nanobeam cavities using atomic layer deposition

Photonic crystal nanobeam cavities are valued for their small mode volume, CMOS compatibility, and high coupling efficiency-crucial features for various low-power photonic applications and quantum information processing. However, despite their potential, nanobeam cavities often suffer from low quality factors due to fabrication imperfections that create surface states and optical absorption. In this work, we demonstrate InP nanobeam cavities with up to 140% higher quality factors by applying a coating of Al 2 O 3 via atomic layer deposition to terminate dangling bonds and reduce surface absorption. Additionally, changing the deposition thickness allows precise tuning of the cavity mode wavelength without compromising the quality factor. This Al 2 O 3 atomic layer deposition approach holds great promise for optimizing nanobeam cavities that are well-suited for integration with a wide range of photonic applications.

42 ENGINEERING↗
DOE OSTI2019

Simulation of an electro-optic modulator based on the quantum-confined Stark effect in a two-layer InAlGaAs rib waveguide on an InP substrate

An electro-optic Mach – Zehnder modulator based on the quantum-confinement Stark effect in layered multiple-quantum-well InAlGaAs structures on InP substrate is numerically simulated. The novelty of the modulator design is the use of a two-layer rib optical waveguides, which provide technologically efficient (loss of 1.5 dB per element) coupling of the modulator with optical fibre. It is shown that, changing the electrode width and the distance between two waveguides in two Mach – Zehnder interferometer arms, one can match the impedance of the modulator with an external 50-Ω load and the velocities of microwave and optical waves in the modulator. The results of the study can be used in integrated optics, optical communication, and radiophotonics devices. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Probing the local electronic structure of isovalent Bi atoms in InP

Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. In this work, we map the spatial pattern of the Bi impurity state, which originates from Bi atoms down to the sixth layer below the surface, in topographic, filled-state X-STM images on the natural {110} cleavage planes. The Bi impurity state has a highly anisotropic bowtielike structure and extends over several lattice sites. These Bi-induced charge redistributions extend along the $\langle$110$\rangle$ directions, which define the bowtielike structures we observe. Local tight-binding calculations reproduce the experimentally observed spatial structure of the Bi impurity state. In addition, the influence of the Bi atoms on the electronic structure is investigated in scanning tunneling spectroscopy measurements. These measurements show that Bi induces a resonant state in the valence band, which shifts the band edge toward higher energies. Furthermore, we show that the energetic position of the Bi-induced resonance and its influence on the onset of the valence band edge depend crucially on the position of the Bi atoms relative to the cleavage plane.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Clean quantum point contacts in an InAs quantum well grown on a lattice-mismatched InP substrate

Strong spin-orbit coupling, the resulting large g factor, and small effective mass make InAs an attractive material platform for inducing topological superconductivity. The surface Fermi level pinning in the conduction band enables highly transparent ohmic contact without excessive doping. In this study, we investigate electrostatically defined quantum point contacts (QPCs) in a deep-well InAs two-dimensional electron gas. Despite the 3.3% lattice mismatch between the InAs quantum well and the InP substrate, we report clean QPCs with up to eight pronounced quantized conductance plateaus at zero magnetic field. Source-drain dc bias spectroscopy reveals a harmonic confinement potential with a nearly 5 meV subband spacing. We find a many-body exchange interaction enhancement for the out-of-plane g factor |$g^{*}_{⊥}$|=27±1 , whereas the in-plane g factor is isotropic |$g^{*}_{x}$|=|$g^{*}_{y}$|=12±2 , close to the bulk value for InAs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Surface chemistry of InP ridge structures etched in Cl{sub 2}-based plasma analyzed with angular XPS

Two x-ray photoelectron spectroscopy configurations are proposed to analyze the surface chemistry of micron-scale InP ridge structures etched in chlorine-based inductively coupled plasma (ICP). Either a classical or a grazing configuration allows to retrieve information about the surface chemistry of the bottom surface and sidewalls of the etched features. The procedure is used to study the stoichiometry of the etched surface as a function of ridge aspect ratio for Cl{sub 2}/Ar and Cl{sub 2}/H{sub 2} plasma chemistries. The results show that the bottom surface and the etched sidewalls are P-rich, and indicate that the P-enrichment mechanism is rather chemically driven. Results also evidence that adding H{sub 2} to Cl{sub 2} does not necessarily leads to a more balanced surface stoichiometry. This is in contrast with recent experimental results obtained with the HBr ICP chemistry for which fairly stoichiometric surfaces have been obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Structural and electrical properties of metamorphic nanoheterostructures with a high InAs content (37-100%) grown on GaAs and InP substrates

A complex study of the structural and electrical properties of nanoheterostructures containing a metamorphic barrier with a high InAs content (37-100%) in the active region have been performed by the Van der Pauw and X-ray diffraction methods. All peaks observed in the rocking curves for the samples studied (throughout the entire structure) have been revealed and identified. It is shown that, having properly chosen the design of the metamorphic buffer and the compositional gradient in it, one can obtain mobilities and concentrations of the 2D electron gas in the In{sub x}Ga{sub 1-x}As quantum well in the heterostructures formed on GaAs substrates that are comparable with the corresponding values for the nanoheterostructures grown on InP substrates. It is established that the mobility and concentration of 2D electron gas depend both on the metamorphic barrier design and on the structural quality of heterostructure as a whole.

77 NANOSCIENCE AND NANOTECHNOLOGY↗