InAs Monolayer Research Articles

Effect of InAs insertion layer on the structural and optical property improvement of InGaAs/InAlAs multiple quantum wells

A 100 periods In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells (MQWs) with and without 2 ML InAs insertion layers (ISLs) were grown on semi-insulating GaAs (001) substrates by molecular beam epitaxy (MBE). The stress-strain was weakened by inserting two monolayers of InAs between the In0.53Ga0.47As well layer and the In0.52Al0.48As barrier layer. High-resolution transmission electron microscopy (HRTEM) was investigated to visually characterize the crystal quality of MQW structures with and without InAs ISLs. The effect of structural and optical properties of the In0.53Ga0.47As/In0.52Al0.48As MQWs by InAs-inserting were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The research shows that the introduction of the 2 ML InAs ISLs can eliminate the strain and reduce the average dislocation density from 2.4×108 cm−2 to 1.4×108 cm−2 in the InGaAs/InAlAs MQWs structure, then control the interface between InGaAs and InAlAs, and finally realize the improvement of the quantum well structural and optical properties with the PL intensity increased by one order of magnitude. Our studies have great significance to the fabrication of GaAs-based multiple quantum well optoelectronic devices, which promote the further development of high-performance versatile optoelectronic applications.

Ballistic transport in sub-10 nm monolayer InAs transistors for high-performance applications.

As an outstanding two-dimensional (2D) semiconductor among III-V compounds, InAs has attracted significant attention due to its much higher electron mobility than silicon and potential for enhanced opportunities in the field of electronic and optical devices. Recently, 2D semiconducting InAs with a thickness of 4.8 nm has been successfully prepared. Here, we systematically investigated the ballistic transport characteristics of sub-10 nm monolayer InAs (InAsH2) metal-oxide-semiconductor field-effect transistors (MOSFETs) by using ab initio quantum transport simulation, which includes on-state current, subthreshold swing, intrinsic delay time, and power consumption. The results suggest that the monolayer (ML) InAsH2 MOSFETs exhibit excellent performance with a beneficial doping concentration and underlap, which can meet the high-performance requirements of the International Technology Roadmap for Semiconductors (ITRS) for the 2013 version until the length of the gate is decreased to 4.0 nm. Moreover, we studied the influence of high-k dielectric effects. We found that both the on-state current and subthreshold swing with a 5.0 nm-gate-length are apparently improved. This work indicates that ML InAsH2 is a suitable nominee for the upcoming generation of channel materials.

N/p-Doping in a buckled honeycomb InAs monolayer using IVA-group impurities.

In this work, the effects of n/p-doping on the electronic and magnetic properties of a low-buckled honeycomb InAs monolayer are investigated using first-principles calculations. Herein, IVA-group atoms (C, Si, Ge, Sn, and Pb) are selected as impurities for n-doping in the In sublattice and p-doping in the As sublattice. The pristine monolayer is a semiconductor with a band gap of 0.77(1.41) as determined using the PBE(HSE06) functional. A single In vacancy induces magnetic semiconductor behavior with a large total magnetic moment of 2.98 μB, while a single As vacancy preserves the non-magnetic nature. The monolayer is not magnetized by n-doping with C and Si atoms due to the strong ionic interactions, while the magnetic semiconducting nature is induced with Ge, Sn, and Pb impurities. In these cases, magnetic properties are produced by IVA-group impurities and their neighboring As atoms. Furthermore, either a magnetic semiconducting or half-metallic nature is obtained via p-doping, whereas magnetism originates mainly from C, Si, Ge, and Sn dopants, and the As atoms closest to a Pb dopant. Further investigation indicates that the magnetization becomes stronger upon increasing the doping level, with a total magnetic moment of up to 3.92 μB with 25% Sn impurity. In addition, the thermal stability of the doped systems at room temperature is also confirmed by ab initio molecular-dynamics (AIMD) simulations. The results introduce IVA-group-assisted functionalization as an efficient way to make prospective 2D InAs-based spintronic materials.

Improvement in Performance of InAs Surface Quantum Dot Heterostructure-Based H2S Gas Sensor by Introducing Buried Quantum Dot Layer

In this work, we have demonstrated InAs surface quantum dot (SQD) based H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas sensors. The epitaxial growth of the strain-coupled and uncoupled InAs/GaAs QD heterostructures is done using the solid-source Molecular Beam Epitaxy (MBE) tool. For both types of heterostructures, the coverage of the InAs monolayer (ML) for the SQD layer varies from 0.9 ML to 2 ML. The ML coverage of the buried quantum dots (BQDs) layer for the coupled heterostructures is kept constant (2.7 ML). The atomic force microscopy results demonstrated that the coupled heterostructures have higher quantum dot density in the SQDs layer in comparison to the uncoupled one due to strain propagation from the BQDs towards the SQD layer. The sensor fabricated using the coupled heterostructure with 2 ML SQDs has demonstrated better performance than the uncoupled one for various concentrations (1 ppm -1000 ppm) of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S gas due to inter-dot carrier tunneling between BQDs and SQDs layer. The coupled InAs gas sensor showed the best sensing properties at room temperature (45.9% sensor response @ 100ppm H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S). We have demonstrated the selectivity of the sensor towards H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S among various target gasses like CO, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and the stability over a longer period of time with only 3% deviation (within acceptable limit). These findings have the potential to promote the fabrication of high-performance gas sensors using SQDs-based coupled heterostructures.

Theoretical Study on Vertically Coupled Stranski-Krastanov (SK) on Sub Monolayer (SML) InAs Quantum Dot Heterostructures Employing Ternary and Quaternary Barrier Materials

This work presents the impact of barrier spacer on the structural and optical properties of strain-coupled Stranski-Krastanov (SK) on Sub Monolayer (SML) quantum dot (QD) heterostructures. Various ternary and quaternary materials have been employed as the barrier layer of SK-SML QD heterostructures. In the coupled SK-SML QDs, the residual strain propagates from the SML seed layer towards the top SK dots, introducing defects and dislocations. After employing the ternary (GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) and quaternary (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.21</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-.0.21-x</sub> As and In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.18</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.82</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) materials, the residual strain reduces, reducing the defects which thereby helps in increasing the crystalline quality of the heterostructure. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nextnano</i> software has been used to compute the structures' strain, energy band profile, probability density functions, and emission wavelength. Two strain components, viz. hydrostatic as well as biaxial strain, have been computed and compared for all the heterostructures to understand the distribution of the strain profile. The emission wavelength is red-shifted for the SK-SML QD heterostructures with ternary and quaternary materials as a barrier layer as compared to that of the GaAs barrier. Moreover, type-I and II energy band profiles are observed for Sb-based barrier material, appropriate for various optoelectronic applications. This is a comparative study of SK-SML QDs with various barrier materials helps minimize the strain and defects and improve the device performance.

Systematic investigation of the mechanical, electronic, and interfacial properties of high mobility monolayer InAs from first-principles calculations.

Due to the excellent electrostatic control, high mobility, large specific surface area, and suitable direct energy gap of two-dimensional (2D) indium arsenide (InAs), it is regarded as one of the most promising alternative channel materials for next-generation electronic and optoelectronic devices. Recently, 2D semiconducting InAs has been successfully prepared. Based on first-principles calculations, we calculate the mechanical, electronic, and interfacial properties of monolayer (ML) fully-hydrogen-passivated InAs (InAsH2) material. The results show that 2D InAsH2 with excellent stability has a suitable logic device band gap (1.59 eV) comparable to silicon (1.14 eV) and 2D MoS2 (1.80 eV), and the electron carrier mobility of ML InAsH2 (490 cm2 V-1 s-1) is twice as large as that of 2D MoS2 (200 cm2 V-1 s-1). In addition, we study the electronic structure of the interfacial contact characteristics of ML half-hydrogen-passivated InAs (InAsH) with seven bulk metals (Ag, Au, Cu, Al, Ni, Pd, Pt) and two 2D metals (ML Ti2C and ML graphene). 2D InAs was metallized after contact with the seven bulk metals and two 2D metals. Based on the above, we insert 2D boron nitride (BN) between ML InAsH and the seven low/high-power function bulk metals to eliminate the interfacial states. Remarkably, the semiconducting properties of 2D InAs with Pd and Pt electrodes are recovered, and 2D InAs achieves p-type ohmic contact with the Pt electrode, which facilitates high on-current and high-frequency operation of the transistor. Hence, this work provides systematic theoretical guidance for the design of next-generation electronic devices.

Short wavelength infrared InPSb/InAs superlattice photodiode grown by metalorganic chemical vapor deposition

We report the growth and characterization of InPSb/InAs superlattice (SL) materials and devices in the short-infrared wavelength range by metalorganic chemical vapor deposition (MOCVD). Good structural quality was achieved with a lattice mismatch of less than 0.09% and smooth surfaces with a roughness of only 0.304 nm. A pin homojunction photodetector with 10 monolayer (ML) InPSb/2 monolayer (ML) InAs SLs on InAs substrate was grown and fabricated. At 77 K, the device demonstrated a 100% cut-off wavelength of ∼2.6 μm, a dark current density of 8.7 × 10−10 A cm−2 at −0.1 V bias voltage, and a specific detectivity of 1.3 × 1013 cm·Hz1/2/W at 2.0 μm.

Characteristics of thin InAlAs digital alloy avalanche photodiodes.

InP-based avalanche photodiodes (APDs) are widely used in short-wave infrared (SWIR) communications. In this work, a thin (200 nm nominal) InAlAs digital alloy layer consisting of two monolayer (ML) InAs and two ML AlAs was grown on InP substrate and investigated in detail. APDs with p-i-n and n-i-p structures were fabricated and characterized. The current-voltage, capacitance-voltage characteristics, and excess noise were measured at room temperature with different laser wavelengths, and the measured effective k value (ratio of impact ionization coefficients) is about 0.15 with the multiplication gain up to 12. The randomly-generated path length (RPL) model was carried out to analyze the dead space effect. Our thin digital alloy successfully reduced excess noise compared with conventional In0.52Al0.48As random alloy without introducing new elements and shows the potential for high-speed, low noise APD applications.

The modeling of a SWIR type-II InAs/AlSb superlattice using an ETBM and interface engineering

A short-wavelength infrared InAs/AlSb type-II superlattice photodetector has been modeled with 15 Mono Layer (ML) of InAs and 4 Mono Layer (ML) of AlSb. In this work, the Empirical Tight-Binding Method (ETBM) was used to calculate the band structure and predict the material of the interfaces. In addition, the effective mass of the heavy hole, light hole, and electron was calculated for each type of the interfaces by tight binding s p 3 s ∗ modeling. Based on the results, the material of the interfaces plays a critical role in lattice mismatch and cutoff wavelength. The detector cutoff wavelength can be changed by atomic engineering of the superlattice interfaces and changing the thicknesses of InAs and AlSb. The simulation results are in good agreement with the experimental values and prove that the [ ( I n A s ) 15 − I n S b − ( A l S b ) 4 − A l A s ] is the most suitable structure. In order to match the simulation results with experimental results, the effect of the segregation on the band structure was evaluated. In this case, the cutoff wavelength of the SWIR detector is 3.27 μ m and the lattice mismatch between the superlattice and the GaSb (100) substrate is 0.63%. • A SWIR InAs/AlSb T2SL photodetector has been modeled with 15 ML of InAs and 4 ML of AlSb. • (ETBM) is used to calculate and predict the material of the interfaces. • The effective mass of the heavy hole, light hole, and electron was calculated for each type of the interfaces by tight binding s p 3 s ∗ modeling. • The flowchart of extracting the band structure by ETBM is presented. • The migration of atoms in interfaces is investigated.

Evolution of InAs quantum dots and wetting layer on GaAs (001): Peculiar photoluminescence near onset of quantum dot formation

InAs quantum dots (QDs) have been grown on a GaAs (001) substrate in the subcritical region of InAs coverage for transition from a 2-dimensional (2D) to a 3-dimensional growth mode. Evolution of QDs and the corresponding wetting layer (WL) with InAs coverage has been investigated. Under specific growth conditions, quantum dot formation was observed only in samples where InAs coverage is more than 1.48 ML. The QD density increases sharply with InAs deposition initially but slows down with increased coverage. Photoluminescence (PL) shows the existence of a third peak, other than QD and WL peaks, at the low energy side of the WL peak, which is named the precursor peak. Evidence is presented supporting the theory that this peak is due to 2D InAs islands on a monolayer of InAs, which are small enough to localize excitons. Meanwhile, the WL peak is due to larger InAs islands under high compressive strain. During QD formation, the WL peak energy increases with the increase in InAs deposition. This is due to the sudden transfer of material from the bigger size of InAs islands to the QD. Our results show that the QD, WL, and precursor peaks coexist near the onset of QD formation. The power dependence of the three PL peaks is evident, which supports to our conclusion.

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).

Purcell Effect and Nonlinear Behavior of the Emission in a Periodic Structure Composed of InAs Monolayers Embedded in a GaAs Matrix

AbstractEnhancement of spontaneous emission in a resonant Bragg quantum well (QW) structure with 60 periods of triple InAs monolayers embedded in a GaAs matrix is studied experimentally and theoretically. From measurements of the time‐resolved photoluminescence, besides the QW exciton at 1.47 eV, a specific super‐radiant (SR) emission demonstrating nonlinear properties is found. The SR mode shows a near‐quadratic dependence of intensity on excitation power, while its energy position follows the Bragg condition. It is revealed that the SR mode shows a peculiar non‐monotonic dependence of intensity on direction, with a maximum observed at approximately 40°. The enhancement in the SR emission at a specific direction is correlated well with suggested theoretical consideration of the modal Purcell factor for periodic quantum well structures.

Investigation of InAs/InGaP nano-heterostructures grown by MOVPE for intermediate band solar cells

InAs/GaInPnano-heterostructures obtained by embedding 1.3 - 2.1 monolayers of InAs in the GaInP matrix lattice-matched to a GaAs substrate have been grown by the MOVPE and investigated. The formation of large nano-objects with lateral size of 150 – 200 nm, which did not depend on the InAs thickness, has been observed by TEM. The nano-objects had aheight of about 10 nm, and their shape can be described as a discontinuous quantum well. Photoluminescence (PL) analysis has shown that the position of the PL peak is practically independent on the InAs thickness and is about 940 nm. It has been supposed that the mechanism of nano-object formation differs from quantum dot deposition in the Stranski-Krastanov growth mode. Probably they are formed due to intensive As-P intermixing, and InAs acts only as nucleus for the further InGaAsP nano-object formation.

Optical studies of InAs/GaAs monolayer Bragg superlattices

Periodic sequences of InAs monolayer in GaAs have been grown by molecular beam epitaxy. The properties of the structure have been modelled by transfer matrix calculation and experimentally studied by time-resolved photoluminescence. The structure obtained provides good localisation of excitons in quantum wells and opens possibilities for various optical effects. Coupling of excitons in quantum wells with electromagnetic field confined by a Bragg arrangement of layers produces a peculiar emission mode – a superradiant mode. Measurements and calculations show that for specific values of frequency of light and angle of emission, enhancement of spontaneous emission rate occurs.

Experimental Study of Spontaneous Emission in the Bragg Multiple Quantum Wells Structure of InAs Monolayers Embedded in a GaAs Matrix

Time-resolved photoluminescence of a Bragg structure of InAs-monolayer quantum wells in GaAs matrix was experimentally studied with. Comparison of luminescence patterns from the side and from the surface of a sample showed that Bragg-type ordering of quantum wells leads to a substantial alteration of the photoluminescence spectra including appearance of additional radiative modes. The sample side spectrum contains a single line corresponding to a ground state of an exciton. The surface spectrum at high excitation levels a new radiation line appears whose frequency and propagation angle correspond to the Bragg condition for quantum wells. A numerical calculation of the modal Purcell factor explains why the radiative emission amplification occurs only at a set of specific angles and frequencies, as opposed to the whole range that satisfies the Bragg condition.

Stacking of InAs QDs with Different Spacer Layer Thickness on GaAs Substrate by Molecular Beam Epitaxy

InAs QDs were grown by supplying 2.5 mono-layers (MLs) of InAs at 500 °C in a molecular beam epitaxial (MBE) system. The QDs are approximately 4–6 nm height with an areal density of 3×85 ×1010 cm−2 for single layer QDs. Typical diameter was found to be about 15–25 nm. InAs QDs were stacked with the spacer layer thickness of 5, 10, 15, 25 and 35 nm. For 15 nm of spacer layer thickness the QDs density decreased to 2.62×1010 cm−2 and again increased for 35 nm spacer layer and reached to the value of 3.65×1010 cm−2. The 14 K photoluminescence (PL) spectra of single layer InAs QDs covered by GaAs layer centered at 1079 nm. For the stacking of InAs QDs with spacer layer thickness of 5 and 10 nm another peak appeared around 1100 nm due to size broadening of QDs because of strain propagation to next layer due to less thickness of spacer layer. When the thickness of the spacer layer increased to 35 nm the peak position is around 1073 nm and the intensity increased more than 3 fold when compare to single layer QDs.

Many-body perturbation theory study of type-II InAs/GaSb superlattices within the GW approximation

Recent studies suggest that the many-body perturbation theory in the partially self-consistent GW (GW0) approximation significantly improves the prediction of band gaps in various semiconductors. In this work, we employed GW formalism to study the electronic structure of type-II InAs/GaSb strained-layer superlattices (T2SLs). T2SLs considered in this study, denoted by (monolayers of InAs, monolayers of GaSb) are (), (), (), (), and (). The InSb-type interfacial layer was introduced in the structures to resemble the actual growth condition in our laboratories. The electronic band gaps are indirect in all the structures. The band gaps at the center of the Brillouin zone show good agreement with experimental data. This study is the first step to investigate the electronic, optical, and defect characteristics of T2SLs within a parameter-free ab initio method.

Impact of temperature and gamma radiation on electron diffusion length and mobility in p-type InAs/GaSb superlattices

The minority carrier diffusion length was directly measured by the variable-temperature Electron Beam-Induced Current technique in InAs/GaSb type-II strain-layer-superlattice infrared-detector structures. The Molecular Beam Epitaxy-grown midwave infrared superlattices comprised 10 monolayers of InAs and 10 monolayers of GaSb to give a total absorber thickness of 4 μm. The diffusion length of minority electrons in the p-type absorber region of the p-type/barrier/n-type structure was found to increase from 1.08 to 2.24 μm with a thermal activation energy of 13.1 meV for temperatures ranging from 77 to 273 K. These lengths significantly exceed the individual 10-monolayer thicknesses of the InAs and GaSb, possibly indicating a low impact of interface scattering on the minority carrier diffusion length. The corresponding minority electron mobility varied from 48 to 65 cm2/V s. An absorbed gamma irradiation dose of 500 Gy halved the minority carrier diffusion length and increased the thermal activation energy to 18.6 meV, due to creation of radiation-induced defect recombination centers.

Defect properties of InGaAsN layers grown as sub-monolayer digital alloys by molecular beam epitaxy

The defect properties of InGaAsN dilute nitrides grown as sub-monolayer digital alloys (SDAs) by molecular beam epitaxy for photovoltaic application were studied by space charge capacitance spectroscopy. Alloys of i-InGaAsN (Eg = 1.03 eV) were lattice-matched grown on GaAs wafers as a superlattice of InAs/GaAsN with one monolayer of InAs (&amp;lt;0.5 nm) between wide GaAsN (7–12 nm) layers as active layers in single-junction solar cells. Low p-type background doping was demonstrated at room temperature in samples with InGaAsN layers 900 nm and 1200 nm thick (less 1 × 1015 cm−3). According to admittance spectroscopy and deep-level transient spectroscopy measurements, the SDA approach leads to defect-free growth up to a thickness of 900 nm. An increase in thickness to 1200 nm leads to the formation of non-radiative recombination centers with an activation energy of 0.5 eV (NT = 8.4 × 1014 cm−3) and a shallow defect level at 0.20 eV. The last one leads to the appearance of additional doping, but its concentration is low (NT = 5 × 1014 cm−3) so it does not affect the photoelectric properties. However, further increase in thickness to 1600 nm, leads to significant growth of its concentration to (3–5) × 1015 cm−3, while the concentration of deep levels becomes 1.3 × 1015 cm−3. Therefore, additional free charge carriers appearing due to ionization of the shallow level change the band diagram from p-i-n to p-n junction at room temperature. It leads to a drop of the external quantum efficiency due to the effect of pulling electric field decrease in the p-n junction and an increased number of non-radiative recombination centers that negatively impact lifetimes in InGaAsN.

Photoelectric characteristics of quantum dots photodetector and fluorescence detection application

ABSTRACTThe photodetector based on AlAs/GaAs/AlAs heterostructures has a layer of self-assembled InAs quantum dots (QDs) and In0.15Ga0.85As quantum well (QW) imbedded in GaAs wide QW. A peculiar negative differential capacitance characteristic has been clearly observed near 100 K. A simple model is proposed and used to qualitatively describe and demonstrated that the InAs monolayer can effectively absorb photo-excited carriers. A high sensitivity micro-spectrometer based on 64 pixels QDs photodetector array has been designed and used for fluorescence detection.