InAs Monolayer Research Articles

Molecular Beam Epitaxy of Zero Lattice-Mismatch InAs/GaSb Type-II Superlattice**Supported by the National Basic Research Program of China under Grant Nos 2015CB351902, 2015CB932402 and 2012CB619203, the National Natural Science Foundation of China under Grant Nos 61177070, 11374295 and U1431231, and the National Key Research Program of China under Grant No 2011ZX01015-001.

Type-II InAs/GaSb superlattices made of 13 InAs monolayers (MLs) and 7 GaSb MLs are grown on GaSb substrates by solid source molecular beam epitaxy. To obtain lattice-matched structures, thin InSb layers are inserted between InAs and GaSb layers. We complete a series of experiments to investigate the influence of the InSb deposition time, V/III beam-equivalent pressure ratio and interruption time between each layer, and then characterize the superlattice (SL) structures with high-resolution x-ray diffraction and atomic force microscopy. The optimized growth parameters are applied to grow the 100-period SL structure, resulting in the full-width half-maximum of 29.55 arcsec for the first SL satellite peak and zero lattice-mismatch between the zero-order SL peak and the GaSb substrate peak.

Potential‐inserted quantum well design for quantum cascade terahertz lasers

We report on a new design of terahertz quantum cascade laser based on a single, potential‐inserted quantum well active region. The quantum well properties are engineered through single monolayer InAs inserts. The modeling is based on atomistic, spds* tight‐binding calculations, and performances are compared to that of the classical three‐well design. We obtain a 100% increase of the oscillator strength per unit length, while maintaining a high, nearly temperature‐independent contrast between phonon‐induced relaxation times of the upper and lower lasing states. The improved performances are expected to allow THz lasing at room temperature.

Nonlinear behavior of the emission in the periodic structure of InAs monolayers embedded in a GaAs matrix

We report time-resolved photoluminescence (TRPL) measurements performed at different temperatures for the Bragg structure containing 60 InAs monolayer-based quantum wells (QWs) periodically arranged in a GaAs matrix. TRPL data reveal an appearance of the additional superradiant (SR) mode originated from coherent collective interaction of QWs. The SR mode is not manifested in the case if a small number of QWs is excited, then only an exciton emission related to the InAs QWs dominates the PL spectrum. The SR mode demonstrates a superlinear dependence of the intensity and radiative decay rate on the excitation power and its intensity increases at elevated temperatures compared to the excitonic emission. The photoluminescence delay time is much shorter for the SR mode indicating that the relaxation of hot excitons can occur via stimulated scattering processes. The specific behavior of the SR emission can have a strong potential for different applications such as optical logic devices, superluminescent diodes, optical switches, and low-threshold lasers. Time-resolved photoluminescence image at low temperature for the Bragg structure consisting of InAs monolayer-based quantum wells (inset).

Growth of Metamorphic InGaAs on GaAs (111)A: Counteracting Lattice Mismatch by Inserting a Thin InAs Interlayer

We have successfully grown high quality InxGa1–xAs metamorphic layer on GaAs (111)A using molecular beam epitaxy. Inserting a thin 3.0–7.1 monolayer (ML) InAs interlayer between the In0.25Ga0.75As and GaAs allowed the formation of a nearly lattice-relaxed In0.25Ga0.75As with a very flat upper surface. However, when the thickness of the inserted InAs is thinner or thicker than these values, we observed degradation of crystal quality and/or surface morphology. We also revealed this technique to be applicable to the formation of a high quality metamorphic InxGa1–xAs layer with a range of In compositions (0.25 ≤ x ≤ 0.78) on GaAs (111)A. Cross-sectional scanning transmission electron microscope studies revealed that misfit dislocations formed only at the interface of InAs and GaAs, not at the interface of In0.25Ga0.75As and InAs. From the dislocation density analysis, it is suggested that the dislocation density was decreased by growing In0.25Ga0.75As on InAs, which effectively contribute the strain relaxatio...

Optical properties of potential-inserted quantum wells in the near infrared and Terahertz ranges

We propose an engineering of the optical properties of GaAs/AlGaAs quantum wells using AlAs and InAs monolayer insertions. A quantitative study of the effects of the monolayer position and the well thickness on the interband and intersubband transitions, based on the extended-basis sp3d5s* tight-binding model, is presented. The effect of insertion on the interband transitions is compared with existing experimental data. As for intersubband transitions, we show that in a GaAs/AlGaAs quantum well including two AlAs and one InAs insertions, a three level {e1 , e2 , e3 } system where the transition energy e3-e2 is lower and the transition energy e2-e1 larger than the longitudinal optical phonon energy (36 meV) can be engineered together with a e3-e2 transition energy widely tunable through the TeraHertz range.

Modeling and simulation of InAs/GaAs quantum dots for solar cell applications

This paper proposes a method of modeling and simulation of InAs/GaAs-based quantum dots (QDs) for solar cell. The main objective is to find the growth parameters in order to produce an optimal double heterostructure using two semiconductor materials InAs and GaAs. We are interested in particular on the impact of the growth control parameters on the physical properties of the two-dimensional InAs mono-layer. We report here a complete but non-exhaustive analysis of the electronic states of the InAs based QDs layers grown on a GaAs substrate. In this work, the reader will find the modeling and the simulation results for both rectangular and elliptical geometries of InAs QDs. In the first part of this work, we provided the change of the electronic transition energy as a function of quantum dots’ radius whilst the second one concerns the absorption coefficient as a function of the incident photon wavelength. The curves we have obtained indicate clearly that the geometrical shape of the InAs QDs does significantly modify the various parameters above. We could therefore confirm that the more appropriate geometry is the elliptical one because of the higher performances.

Super-radiant mode in InAs—monolayer–based Bragg structures

We report direct experimental evidence of the collective super-radiant mode in Bragg structure containing 60 InAs monolayer-based quantum wells (QWs) periodically arranged in GaAs matrix. Time-resolved photoluminescence measurements reveal an appearance of the additional super-radiant mode, originated from coherent collective interaction of QWs. This mode demonstrates a super-linear dependence of the intensity and radiative decay rate on the excitation power. The super-radiant mode is not manifested in the case if only a small number of QWs is excited.

Investigation of the shape of submonolayer quantum dots using a polarization-dependent photocurrent

Structural and optical characterization of multi-stack InAs/InGaAs submonolayer quantum dots (SML-QDs) grown under the Stranski–Krastanov growth mode was performed via a polarization-dependent study. Various angular in-plane (plane perpendicular to growth direction) and out-of-plane (plane parallel to the 45°-polished facet) polarization-dependent spectral photocurrents were measured to investigate the three-dimensional quantum confinement in multi-stack 0.3 monolayer InAs SML-QDs (the shape of SML-QDs embedded in an SML-QD based photodetector). Scanning transmission electron microscopy images revealed the interdiffusion of indium atoms between SML-QDs and the InGaAs quantum well due to an insufficient amount of indium, which agrees well with the tendency of s- to z-polarized response ratios.

Structural and optical characterization of InAs/GaSb type-II superlattices: Influence of the change in InAs and GaSb layer thicknesses for fixed InSb-like interfaces

In this article, we report on the molecular beam epitaxy growth and characterization of a 140 period InAs/GaSb type-II superlattice structure designed for mid infrared detection. Thickness of a period was systematically altered in each sample by changing the thickness of InAs (GaSb) layers from 9 to 7 monolayers (ML) for a fixed GaSb (InAs) layer at 9 ML (7 ML). The same InSb-like strain compensation interface was used for all samples. High resolution X-ray diffraction analysis, spectral responsivity and external quantum efficiency (QE) measurements were performed to express the effects of layer thickness variations on both structural and photodetector features. The decrease in the InAs thickness resulted in the increased mismatch from 0 to +1626ppm and the blue shift in the 50% cut-off wavelength (λc) from 5.41 to 4.36μm at 77K. The additional decrease in GaSb thickness caused further increase in the mismatch up to +1791ppm. The steepness of the photoresponse at the absorption band edge was quantified and presented comparatively with different photodetector parameters and material properties for a complete picture. The highest optical response was obtained from sample having 8 ML InAs and 9 ML GaSb with λc=4.76μm and QE=23.7% at 4μm.

Droplet epitaxy growth of telecom InAs quantum dots on metamorphic InAlAs/GaAs(111)A

We demonstrated the droplet epitaxial growth of InAs quantum dots on a GaAs(111)A substrate, which emitted at telecommunication wavelengths. A high-quality metamorphic In0.52Al0.48As layer was formed by inserting three monolayers of InAs between GaAs(111)A and InAlAs. InAs quantum dots were grown on the InAlAs surface by droplet epitaxy. They exhibited a laterally symmetrical shape owing to the C3v symmetry of the {111} surface. The photoluminescence signals of capped quantum dots indicated broadband spectra covering wavelengths from 1.3 to 1.55 µm. Thus, our dots are potentially useful for constructing entangled photon sources compatible with current telecommunication networks.

Photoelectric Characteristics of Double Barrier Quantum Dots-Quantum Well Photodetector

The photodetector based on double barrier AlAs/GaAs/AlAs heterostructures and a layer self-assembled InAs quantum dots and In0.15Ga0.85As quantum well (QW) hybrid structure is demonstrated. The detection sensitivity and detection ability under weak illuminations have been proved. The dark current of the device can remain at 0.1 pA at 100 K, even lower to3.05×10-15 A, at bias of −1.35 V. Its current responsivity can reach about6.8×105 A/W when 1 pw 633 nm light power and −4 V bias are added. Meanwhile a peculiar amplitude quantum oscillation characteristic is observed in testing. A simple model is used to qualitatively describe. The results demonstrate that the InAs monolayer can effectively absorb photons and the double barrier hybrid structure with quantum dots in well can be used for low-light-level detection.

Electrical modeling of InAs/GaSb superlattice mid-wavelength infrared pin photodiode to analyze experimental dark current characteristics

Dark current characteristics of 7 Monolayers (ML) InAs/ 4 ML GaSb SL pin photodiodes are simulated using ATLAS software. Using appropriate models and material parameters, we obtain good agreement between the simulated and the experimental dark current curves of photodiodes grown by molecular beam epitaxy. The n-type non-intentionally-doped (nid) SL samples exhibit a dependence of the lifetime with temperature following the T−12 law, signature of Shockley-Read-Hall (SRH) Generation-Recombination current. We also studied the dependence of the dark current with the absorber doping level. It appears that the absorber doping level must not exceed a value of 2 × 1015 cm−3, above this value the dark current is increasing with increased doping level. However for this doping value, a dark current as low as 5 × 10−9 A/cm2, at 50 mV reverse bias at 77 K can be obtained.

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 GaAs0.51Sb0.49 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/GaAs0.51Sb0.49 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.

Investigation of impurities in type-II InAs/GaSb superlattices via capacitance-voltage measurement

Capacitance-voltage measurement was utilized to characterize impurities in the non-intentionally doped region of Type-II InAs/GaSb superlattice p-i-n photodiodes. Ionized carrier concentration versus temperature dependence revealed the presence of a kind of defects with activation energy below 6 meV and a total concentration of low 1015 cm−3. Correlation between defect characteristics and superlattice designs was studied. The defects exhibited a p-type behavior with decreasing activation energy as the InAs thickness increased from 7 to 11 monolayers, while maintaining the GaSb thickness of 7 monolayers. With 13 monolayers of InAs, the superlattice became n-type and the activation energy deviated from the p-type trend.

Improvement of QDIP performance due to quantum dots with built-in charge

The charging of quantum dots provides two strong effects which improve Quantum Dot Infrared Photodetector (QDIP) performance. First, electrons placed in the quantum dots enhance IR-induced transitions and increase electron coupling to IR radiation. Second, the built-in-dot charge creates potential barriers around dots and these barriers strongly suppress the photoelectron capture and exponentially increase the photoelectron lifetime. Both effects enhance the IR photoresponse. Long photoelectron lifetime decreases the generation–recombination noise and increases the device sensitivity. To investigate the potential profiles around charged dots, we used the nextnano3 software which allows for simulation of multilayer structures combined with realistic geometries in one, two, and three spatial dimensions. In weak electric fields the photoelectron kinetics and transport in the potential created by charged dots have been studied analytically. In strong fields the results were based on Monte-Carlo modeling. The effects of dot charging have been investigated in QD structures which were fabricated using molecular beam epitaxy. InAs quantum dots were grown on AlGaAs surfaces by deposition of approximately 2.1 monolayers of InAs. In the obtained structures the dot charging is realized via intra-dot and inter-dot doping. The increase in photoresponse due to dot charging is in good agreement with the model which takes into account anisotropy of potential barriers around QDs in QD layers.

Broadband InGaAs-capped InAs/GaAs quantum-dot infrared photodetector with Bi-modal dot height distributions

The influence of quantum-dot (QD) height distribution on the detection wavelengths of InGaAs-capped quantum-dot infrared photodetectors (QDIPs) is investigated. For devices with 2.8 and 2.0 mono-layer (ML) InAs coverage, 7.6 and 10.4 μm detection wavelengths are observed. The results suggest that reduced dot height would result in a longer detection wavelength. By using 2.4 ML InAs QDs with bi-modal dot height distributions, a 6–12 μm broadband QDIP is achieved with the combination of ∼8 and ∼10 μm peak detection wavelengths contributed by the larger and smaller InAs QDs.

Optical properties of ultrathin InAs quantum-well-heterostructures

Band structure calculations of complete InAs monolayer in AlGaAs/GaAs quantum wells are performed within the framework of the extended-basis sp3d5s* tight-binding model. We show that the optical properties can be tuned from the quantum well energy below the GaAs band-gap depending on the well thickness and the position of the probe. The results are supported by differential reflectivity measurements and represent a concept for optoelectronic devices with an operation wavelength widely tuneable around 850 nm employing GaAs process technology.

Morphology and shape dependent characteristics of InAs/InP(1 0 0) quantum dot laser grown by gas source molecular beam epitaxy

We report on the low-dimensional InAs quantum dot lasers based on the InP(100) substrate grown by gas source molecular beam epitaxy. The active regions of laser consist of fivefold-stacked InAs layer with thickness of 3.0 and 3.5 monolayers (MLs), respectively. Ridge waveguide quantum dot lasers were fabricated and the characteristics of the lasers were carefully examined under continuous-wave mode. A laser with InAs thickness of 3.0 MLs shows a better performance than that of laser comprised of 3.5 MLs InAs. The deteriorated performance from 3.5 MLs lasers is attributed to the morphology and shape of quantum dot elongated along [01–1] direction, which partly decrease quantum efficiency and density of states.

Temperature Dependence of Spin Relaxation Time in InAs Columnar Quantum Dots at 10 to 150 K

We have investigated carrier spin relaxation in InAs columnar quantum dots (CQDs) using time-resolved photoluminescence measurement. The CQDs were formed by depositing a 1.8 monolayer InAs seed dot layer and a short-period GaAs/InAs superlattice (SL). The spin relaxations of the 3- and 35-period SL CQDs show double exponential decay up to 50 and 130 K, respectively. The spin relaxation times of the fast component, whose amplitudes are 4–11 times larger than that of the slow component, are around 100 ps for the two samples. For the 3-period SL CQDs, the fast spin relaxation time shows no temperature dependence up to around 50 K, indicating the relevance of the Bir-Aronov-Pikus process. The slow spin relaxation time of the 35-period SL CQDs was found to decrease from 3.42 ns at 10 K to 0.849 ns at 130 K. This large change may be explained by the Elliott–Yafet process considering acoustic phonon scattering.

Zinc-blende MnAs thin films directly grown on InP (001) substrates as possible source of spin-polarized current

We have directly grown zinc-blende (zb)-type MnAs thin films on InP (001) substrates without the aid of any buffer layer using molecular beam epitaxy (MBE). From the High-resolution X-ray diffraction (XRD) data, assuming face-centered cubic (fcc) MnAs structure, the average lattice constants values were calculated to be 6.068 and 6.060 Å for growth temperatures of 250 and 300 °C, respectively. High-resolution transmission electron microscopy (TEM) investigations and selected-area electron-diffraction (SAD) verified the successful growth of zb-type cubic MnAs coexisting with the NiAs-type hexagonal MnAs. The saturation magnetization was estimated to be 300 emu/cm 3 determined from the magnetic field dependence of the magnetization curves. From the temperature dependence of magnetization, the Curie temperature was found to be approximately 308 K. Success in the growth of zb-type MnAs thin films could be reasonably explained by the existence of a monolayer of InAs at the interface between the MnAs and InP substrates.