Epitaxial InAs Research Articles

Терагерцевая генерация в эпитаксиальных пленках InAs

We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser’s stability.

Terahertz generation in InAs epitaxial films

We present the results of terahertz generation studies under excitation via femtosecond lasers pulses epitaxial films of InAs, which were synthesized on semi-insulating and highly doped GaAs substrates. It is shown that a terahertz emitter based on epitaxial InAs film grown on a heavily doped GaAs n-type substrate, has the same terahertz generation efficiency as the InAs-film emitter grown on a semi-isolating GaAs substrate, but it has a significantly better spectral resolution, which is mainly determined by the parameters of the optical delay line and the femtosecond laser's stability. Keywords: coherent terahertz emitter, InAs epitaxial film, molecular beam epitaxy

Epitaxial type-I and type-II InAs-AlAsSb core–shell nanowires on silicon

Low-bandgap semiconductor nanowires (NWs) attract considerable interest for mid-infrared (MIR) photonics and optoelectronics, where ideal candidate materials require surface-passivated core–shell systems with large tunability in band offset, lineup, and emission wavelength while maintaining close lattice-matching conditions. Here, we propose and demonstrate epitaxial InAs–AlAsSb core–shell NW arrays on silicon (Si) that offer exceptional control over both the internal strain close to lattice-matching as well as band lineups tunable between type-I and type-II, with almost no analogue in the III–V materials family. We develop direct monolithic growth of high-uniformity InAs–AlAsSb NWs with wide tunability in shell composition and employ correlated Raman scattering and micro-photoluminescence spectroscopy to elaborate the interplay among hydrostatic strain, band lineup, and emission energy of the NW core luminescence tuned from ∼0.4 to 0.55 eV. Electronic structure calculations further support the experimentally observed tunability between type-I and type-II band lineups. The Si-integrated InAs-AlAsSb NW materials system holds large prospects not only for on-chip MIR photonics but also for other applications including high-speed transistors and NW-based hot carrier solar cells.

Спектральные и электрические свойства светодиодных гетероструктур с активной областью на основе InAs

The results of the study of optical and structural properties of epitaxial InAs layers grown on an n-InAs substrate, and spectral and electrical properties of light-emitting diode (LED) heterostructures with an InAs active layer and various design and chemical composition of barrier layers are presented; the properties of heterostructures were studied in the temperature range 4.2−300 K. A significant influence of the degree of substrate doping and the properties of heterointerfaces on the form of emission spectra and power characteristics of heterostructures is shown. The mechanisms of the carrier transport are studied, and the prevalence of the diffusion component of the current at temperatures above 200 K and the presence of the tunneling component at lower temperatures are shown.

Toward durable Al-InSb hybrid heterostructures via epitaxy of 2ML interfacial InAs screening layers

The large Land\'{e} g-factor, high spin-orbit coupling, and low effective mass of the two-dimensional electron gas in InSb quantum wells combined with proximal superconductivity may realize a scalable platform for topological quantum computation. Aluminum thin films directly deposited on top of InSb planar structures result in the formation of a reactive AlInSb layer at the interface. This interlayer progressively consumes the whole Al film, resulting in a disordered AlInSb layer after few months at room temperature. We report on a heterostructure design that results in a significant increase of the durability of these hybrid Al-InSb heterostructures with the preservation of a pure Al film and sharp superconductor-semiconductor interface for more than one year. Two monolayers of epitaxial InAs at the superconductor-semiconductor interface prevent interfacial reactivity as evidenced by X-ray reflectivity and energy dispersive spectroscopy measurements. Structural characterizations of the Al films by transmission electron microscopy reveal the presence of tens of nanometers wide grains predominantly oriented with Al(110) parallel to InSb(001).

Dislocation tolerance in InAs quantum dots determined by operating temperature

Researchers show that carrier recombination at dislocations is a strong function of temperature in epitaxial InAs quantum dots on silicon.

Photonic engineering of highly linearly polarized quantum dot emission at telecommunication wavelengths

In this work, we discuss a method to control the polarization anisotropy of spontaneous emission from neutral excitons confined in quantum-dot-like nanostructures, namely single epitaxial InAs quantum dashes emitting at telecom wavelengths. The nanostructures are embedded inside lithographically defined, in-plane asymmetric photonic mesa structures, which generate polarization-dependent photonic confinement. First, we study the influence of the photonic confinement on the polarization anisotropy of the emission by photoluminescence spectroscopy, and we find evidence of different contributions to a degree of linear polarization (DOLP), i.e., from the quantum dash and the photonic mesa, in total giving rise to $\mathrm{DOLP}=0.85$. Then, we perform finite-difference time-domain simulations of photonic confinement, and we calculate the DOLP in a dipole approximation showing well-matched results for the established model. Furthermore, by using numerical calculations, we demonstrate several types of photonic confinements where highly linearly polarized emission with DOLP of about 0.9 is possible by controlling the position of a quantum emitter inside the photonic structure. Then, we elaborate on anisotropic quantum emitters allowing for exceeding $\mathrm{DOLP}=0.95$ in an optimized case, and we discuss the ways towards efficient linearly polarized single photon source at telecom bands.

Confinement regime in self-assembled InAs/InAlGaAs/InP quantum dashes determined from exciton and biexciton recombination kinetics

The exciton and biexciton confinement regimes in strongly anisotropic epitaxial InAs nanostructures called quantum dashes (QDashes) embedded in an In0.53Ga0.23Al0.24As matrix, which is lattice-matched to InP(001) substrate, have been investigated. For that purpose, we have performed low-temperature spatially and polarization-resolved photoluminescence and time-resolved photoluminescence measurements on a set of single QDashes. The main conclusions are drawn based on the experimentally obtained distribution of the ratio between the exciton and biexciton lifetimes. We have found that a majority of QDashes for which the abovementioned ratio falls into the range of 1.2 ± 0.1–1.6 ± 0.1 corresponds to the so called intermediate confinement regime, whereas for several cases, it is close to 1 or 2, suggesting reaching the conditions of weak and strong confinement, respectively. Eventually, we support this data with dependence of the lifetimes' ratio on the biexciton binding energy, implying importance of Coulomb correlations, which change significantly with the confinement regime.

Observation of partial relaxation mechanisms via anisotropic strain relief on epitaxial islands using semiconductor nanomembranes

In this work we attempt to directly observe anisotropic partial relaxation of epitaxial InAs islands using transmission electron microscopy (TEM) and synchrotron x-ray diffraction on a 15 nm thick InAs:GaAs nanomembrane. We show that under such conditions TEM provides improved real-space statistics, allowing the observation of partial relaxation processes that were not previously detected by other techniques or by usual TEM cross section images. Besides the fully coherent and fully relaxed islands that are known to exist above previously established critical thickness, we prove the existence of partially relaxed islands, where incomplete 60° half-loop misfit dislocations lead to a lattice relaxation along one of the 〈110〉 directions, keeping a strained lattice in the perpendicular direction. Although individual defects cannot be directly observed, their implications to the resulting island registry are identified and discussed within the frame of half-loops propagations.

Optical control of spectral diffusion with single InAs quantum dots in a silver-embedded nanocone

We study the spectral diffusion in a single epitaxial InAs quantum dot placed in a silver-embedded nanocone structure. Making use of a series of stroboscopic detection of optical transitions, we demonstrate the temporal fluctuations in peak energy of photoluminescence. In particular, the photoluminescence fluctuations can be effectively suppressed by strong illumination. By analyzing the photon statistics, we find that the dot emission exhibits stable non-classical nature with the strong anti-bunching behavior after this stabilization.

Characterization of encapsulated quantum dots via electron channeling contrast imaging

A method for characterization of encapsulated epitaxial quantum dots (QD) in plan-view geometry using electron channeling contrast imaging (ECCI) is presented. The efficacy of the method, which requires minimal sample preparation, is demonstrated with proof-of-concept data from encapsulated (sub-surface) epitaxial InAs QDs within a GaAs matrix. Imaging of the QDs under multiple diffraction conditions is presented, establishing that ECCI can provide effectively identical visualization capabilities as conventional two-beam transmission electron microscopy. This method facilitates rapid, non-destructive characterization of sub-surface QDs giving immediate access to valuable nanostructural information.

Growth of Catalyst-Free Epitaxial InAs Nanowires on Si Wafers Using Metallic Masks.

Development of heteroepitaxy growth of catalyst-free vertical III-V nanowires on Si wafers is highly desirable for future nanoscale Si-based electronic and optoelectronic devices. In this study, a proof-of-concept approach is developed for catalyst-free heteroepitaxy growth of InAs nanowires on Si wafers. Before the growth of InAs nanowires, a Si-compatible metallic film with a thickness of several tens of nanometers was predeposited on a Si wafer and then annealed to form nanosize openings so as to obtain a metallic mask. These nano-openings exposed the surface of the Si wafer, which allowed subsequent nucleation and growth of epitaxial InAs nanowires directly on the surface of the Si wafer. The small size of the nano-openings limits the lateral growth of the nanostructures but promotes their axial growth. Through this approach, catalyst-free InAs nanowires were grown on both Si (111) and (001) wafers successfully at different growth temperatures. In particular, ultralong defect-free InAs nanowires with the wurtzite structure were grown the Si (111) wafers at 550 °C using the Ni mask. This study offers a simple, cost-effective, and scalable method to grow catalyst-free III-V nanowires on Si wafers. The simplicity of the approach opens a new avenue for the growth and integration of catalyst-free high-quality heteroepitaxial III-V nanowires on Si wafers.

Temperature-dependent modulated reflectance and photoluminescence of InAs–GaAs and InAs–InGaAs–GaAs quantum dot heterostructures

Optical transitions and electronic properties of epitaxial InAs quantum dots (QDs) grown with and without InGaAs strain-relieving capping layer within GaAs/AlAs quantum well (QW) are investigated. Modulated reflectance and photoluminescence spectroscopy is used to probe the QD- and QW-related interband optical transitions over the temperature range of 3–300 K. The observed spectral features in QDs are identified using numerical calculations in a framework of 8-band $$k\cdot p$$ method. It is found that covering the dots by a 5 nm-thick InGaAs layer yields the energy red-shift of ground-state transition by $${\sim }150\,{\text{ meV}}$$ . Moreover, the analysis of interband transition energy dependence on temperature using Varshni expression shows that material composition of InAs QDs significantly changes due to Ga/In interdiffusion. A comparison of emission- and absorption-type spectroscopy applied for InAs–GaAs QDs indicates a Stokes shift of $${\sim }0.02\,{\text{ meV}}$$ above 150 K temperature.

Site-controlled InAs quantum dot chains coupled to surface plasmons

Plasmonic hybrid nanostructures are material combinations where the plasmonic metal structure enables optical field confinement, while the other ingredients provide additional functionality, such as emission, absorption, or optical nonlinearity. In particular, epitaxial InAs quantum dots (QDs) embedded in a single-crystal GaAs matrix are highly efficient quantum emitters that can be integrated as plasmonic–semiconductor hybrids to realize various on-chip functions. In this Letter, we demonstrate QD–plasmon coupling in a hybrid structure consisting of site-controlled InAs/GaAs quantum dot chains (QDCs) in the proximity of an Ag film. The optical properties of the QDC–plasmon system are investigated using a cleaved-edge photoluminescence (PL) geometry, which allows us to probe the vertical and horizontal polarizations of the PL emission. We demonstrate plasmonic enhancement of both PL decay rate and vertical polarization of the PL emission with decreasing separation of the QDCs and the Ag film. The ability to couple site-controlled InAs QDCs with surface plasmons is a significant step toward exploitation of high-quality epitaxial quantum dots as gain or loss compensation in subwavelength plasmonic metal structures, such as waveguide networks, quantum plasmonic structures, and metamaterials.

Short-wavelength infrared photodetector on Si employing strain-induced growth of very tall InAs nanowire arrays

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4–3 μm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations, and is also cost-effective. InAs NW arrays with an average height of 50 μm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 108 cm·Hz1/2/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

Controlling the crystal phase and structural quality of epitaxial InAs nanowires by tuning V/III ratio in molecular beam epitaxy

In this study, we demonstrated the control of crystal phase and structural quality of Au-catalyzed InAs nanowires grown on the GaAs {111}B substrates by tuning the V/III ratio in molecular beam epitaxy. It has been found that InAs nanowires can only be grown in a relatively narrow window of the V/III ratio. It is also demonstrated that the V/III ratio can be used to control the structural quality of wurtzite structured and zinc-blende structured InAs nanowires under low V/III ratios, and defect-free wurtzite structured and zinc-blende structured InAs nanowires were successfully achieved. This study provides an insight into the controlled growth of high-quality wurtzite structured and zinc-blende structured InAs nanowires through the V/III ratio engineering.

Quality of epitaxial InAs nanowires controlled by catalyst size in molecular beam epitaxy

In this study, the structural quality of Au-catalyzed InAs nanowires grown by molecular beam epitaxy is investigated. Through detailed electron microscopy characterizations and analysis of binary Au-In phase diagram, it is found that defect-free InAs nanowires can be induced by smaller catalysts with a high In concentration, while comparatively larger catalysts containing less In induce defected InAs nanowires. This study indicates that the structural quality of InAs nanowires can be controlled by the size of Au catalysts when other growth conditions remain as constants.

Epitaxial growth of engineered metals for mid-infrared plasmonics

The authors demonstrate the ability of high-quality epitaxial InAs films to be used as wavelength-flexible, low-loss, engineered plasmonic metals across the mid-infrared spectral range. Films are grown by molecular beam epitaxy and characterized by Hall effect measurements, atomic force microscopy, and infrared reflection and transmission spectroscopy. The losses of our plasmonic material are studied as a function of InAs doping density, growth rate, buffer layer type, and substrate type. High growth rates are shown to be integral to obtaining films with low losses and doping densities approaching 1×1020 cm−3.

Correlation between adatom dynamics and electron accumulation at the epitaxial InAs(111)A surface

Indium adatoms remaining at the InAs(111)A surface after molecular beam epitaxy were characterized by a low-temperature scanning tunneling microscope at 5K. The resonance spectrum of the adatom orbital was analyzed including the tip-induced line width broadening effect. The energy difference between the resonance level and surface Fermi level was estimated to be 0.79eV at 420°C, which is equivalent to the adatom desorption energy of 0.8eV previously reported. The adatom desorption dynamics was modeled on the basis of the comparison between the period of the phonon-assisted inelastic electron tunneling and the electron lifetime at the adatom resonance level. The calculated temperature range of the adatom desorption excellently agrees with the reported experimental one. It is suggested that the adatom density was almost completely maintained and observed at 5K as it was at 420°C (693K).

Palladium Catalyzed Defect-free Zinc-Blende Structured InAs Nanowires

ABSTRACTIn this study, Pd thin film is used as catalyst to grow epitaxial InAs nanowires on GaAs(111)B substrate in a metal-organic chemical vapor deposition reactor to explore the growth mechanism and the effects of non-gold catalysts in the growth of III-V epitaxial nanowires. Through detailed morphological, structural and chemical characterization using scanning and transmission electron microscopy, it is found that defect-free zinc-blende structured epitaxial InAs nanowires are grown along the <110> directions with four {111} sidewall facets forming a diamond shaped cross-section. Furthermore, the interface between the nanowire/catalyst is found to be the uncommon {113} planes. It is anticipated that these zinc-blende structured InAs nanowires are grown via the vapor-liquid-solid mechanism. The defect-free nature of these nanowires arises from the non-<111> growth direction and non-{111} nanowire/catalyst interface.