Strained InAs Quantum Research Articles

Effect of InAs quantum dots capped with GaAs on atomic-scale ordering in Ga0.5In0.5P

The CuPt ordering of the group III elements in GaxIn1-xP (x ≃ 0.5) has been observed to vary during growth by metalorganic vapor-phase epitaxy of InAs quantum dots capped with GaAs in a GaInP matrix. While ordering is not affected by the insertion of a GaAs layer, the growth of InAs quantum dots capped with GaAs results in ordered, partially ordered, or fully disordered GaInP. We show that the degree of ordering depends on the deposition time of the InAs quantum dots and on the thickness of the GaAs capping layer. Our results indicate that disordered GaInP occurs in the presence of excess indium at the growth surface, which results from the growth of strained InAs quantum dots. Ordering resumes when the excess indium is consumed. Cathodoluminescence, scanning transmission electron microscopy, and atomic force microscopy are used in this study to correlate the electronic properties and the microstructure of the thin films.

Coherently strained in-plane atomic layer heterojunctions

Semiconductor heterojunctions (HJs) have played a critical role in many modern electronic and photonic devices. The emergence of transition metal dichalcogenides (TMDs) as a new class of two-dimensional semiconducting materials creates exciting new opportunities to push semiconductor heterostructures toward a new frontier. Vertically stacked van der Waals heterostructures have been quickly recognized as a powerful platform to create atomically thin heterostructures.1 Recently, attention has been directed to the creation of monolayer ‘lateral heterojunctions’ with a line interface between two different TMDs, pushing semiconductor HJs to a new dimension. In late 2014, three papers published simultaneously, demonstrating direct growth of lateral heterojunctions using chemical vapor deposition.2, 3, 4 The papers demonstrated growth including both lattice matched and mismatched HJs; however, the interfaces were not chemically abrupt (that is, diffuse interface). In particular, the lattice mismatched system (for example, WS2-WSe2) displayed a compositional transition width of 40 nm. Presumably, the gradual composition alleviates the abrupt change of the lattice constant, similar to the epitaxial growth of conventional heterostructures with a large lattice mismatch. Conventional wisdom suggests a chemically abrupt lateral interface in a lattice mismatched system would be difficult to achieve. In contrast, in 2015 by using a two-step process, Li et al.5 reported the successful growth of lattice-mismatched lateral HJs of WSe2–MoS2 with an atomically abrupt compositional interface as shown schematically in Figure 1a. This system is coherently strained judging by the high Photoluminescence efficiency of individual TMDs. This scenario is similar to the growth of coherently strained InAs quantum dots in GaAs, although in this case, compositional mixing at the interface has been difficult to eliminate. Thus, an atomically abrupt compositional interface in a system with such a large lattice mismatch comes as a pleasant surprise.

Investigation and optimization of intraband electromagnetically induced transparency in strained InAs quantum dot/wetting layer structures

In this work, effects of the shape and size on the optical properties and optimization of the intersubband electromagnetically induced transparency in the Infra-red region of three-dimensional strained truncated pyramid-shaped InAs/GaAs quantum dot (QD) were investigated in detail. More precisely, within the density matrix approach, the probe absorption and group velocity along with the refractive index of the medium were studied with respect to their dependence on the dephasing rates and the Rabi frequencies of the probe and coupling fields for different QD heights and wetting layer (WL) thicknesses. It is found that the slow-down factors, group index, and absorption coefficient are inversely proportional to the width of the transparency window and proportional to the depth of the transparency window. The optimized transparency window can be achieved by varying the dot height and the WL thickness such that the tall dots with thin WL thickness induce significant enhancements at a fixed resonant peak position of Rabi frequency of the coupling field. The physical reasons behind these interesting phenomena were also explained based on the polarized features of intersubband transitions.

Effect of Bi isovalent dopants on the formation of homogeneous coherently strained InAs quantum dots in GaAs matrices

The distribution of hydrostatic strains in Bi3+-doped InAs quantum dots embedded in a GaAs matrix are calculated in the context of the deformation-potential model. The dependences of strains in the material of spherical InAs quantum dots with substitutional (Bi → As) and interstitial (Bi) impurities on the quantum-dot size are derived. The qualitative correlation of the model with the experiment is discussed. The data on the effect of doping on the morphology of self-assembled InAs:Bi quantum dots in a GaAs matrix are obtained.

Highly strained InAs quantum wells on InP substrates for mid-IR emission

Optical emission characteristics of indium arsenide (InAs) quantum wells were studied using organometallic vapor phase epitaxy (OMVPE). Low growth temperature (<500 °C) and tertiarybutylarsine (TBA) and/or arsine precursors were applied for this study. Several growth parameters such as growth temperature, growth rate, interruption time between growths of layers, and mixture of group V precursors were investigated. It was found that relatively high growth rate of InAs (0.3 nm/s) and a mixture flow of TBA and AsH 3, allowed growth of up to 9 nm thick InAs quantum wells without significant strain relaxation. Photoluminescence (PL) wavelengths of 2.52 μm were observed at room temperature (RT) from a 9 nm InAs double quantum well (DQW) in a separate confinement hetero-structure (SCH) structure.

Anomalous magnetotransport and cyclotron resonance of high mobility magnetic 2DHGs in the quantum Hall regime

Low-temperature magnetotransport measurements and far-infrared transmission spectroscopy are reported in molecular beam epitaxial grown two-dimensional hole systems confined in strained InAs quantum wells with magnetic impurities in the channel. The interactions of the free holes spin with the magnetic moment of 5/2 provided by manganese features intriguing localization phenomena and anomalies in the Hall and the quantum Hall resistance. In magnetic field-dependent far-infrared spectroscopy measurements well-pronounced cyclotron resonance and an additional resonance are found that indicates an anti-crossing with the cyclotron resonance.

Reliable 2.3-$\mu$m Wavelength Highly Strained InAs–InP MQW-DFB Lasers With p-/n-InP Buried Heterostructure

We have realized reliable 2.3-mum wavelength InAs-InP multiquantum-well distributed-feedback (DFB) lasers for trace gas monitoring applications. The estimated median lifetime exceeds 1x105 hours during aging at an ambient temperature of 45degC and with a constant output power of 3 mW. Furthermore, the relative increase in operating current is proportional to the square root of time, and it is clarified that the main degradation mechanism in DFB lasers with highly strained InAs quantum wells is dominated by a diffusion process as found with conventional telecommunication lasers.

Magnetic ordering effects in a Mn-modulation-doped high mobility two-dimensional hole system

We have studied the magnetotransport properties of a manganese (Mn)-modulation-doped high mobility two-dimensional hole system in a strained InAs quantum well (QW) structure. At precisely $T=600\text{ }\text{mK}$ a phase transition from paramagnetism to ferromagnetism can be observed by a change of the low-field magnetotransport behavior and hysteresis. In the magnetically ordered phase a superposition of positive magnetoresistance and weak antilocalization was detected in the longitudinal resistance ${R}_{xx}$ and in the Hall resistance ${R}_{xy}$ a superposition of normal, anomalous, and planar Hall effects demonstrating spontaneous magnetization in the QW plane was detected. From extensive analysis of the temperature and magnetic field dependence of the Shubnikov--de Haas oscillations we deduce the effective mass, transport, and quantum-scattering times. The latter indicates presence of small-range scattering potential. From corrections to the Drude conductivity we determine the impurity interaction time, which is significantly reduced in the ferromagnetic phase indicating interaction of the two-dimensional free holes' spin with the localized magnetic moments of 5/2 from Mn ions.

Strained Quantum Well InAs Micro-Hall Sensors: Dependence of Device Performance on Channel Thickness

Magnetic sensitivity and low-frequency noise in micro-Hall sensors based on pseudomorphic InAs quantum well channels are investigated as functions of InAs thickness. The strained InAs quantum wells with thickness between 0 and 20 Aring are added into lattice-matched doped channel In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As/InP heterostructures and enhance the absolute magnetic sensitivity by increasing the electron mobility. We show that the increase of the InAs channel thickness also leads to a significant reduction of the low-frequency noise. The result is an improved magnetic field detection over a broad frequency range. A minimum magnetic field detection limit of nT is resolved by a 40-m wide doped channel micro-Hall device at frequencies around kHz.

In As ∕ In Ga As P sidewall quantum dots on shallow-patterned InP (311)A

Highly strained InAs quantum dots (QDs) embedded in InGaAsP are formed at the fast-growing [01−1] mesa sidewall on shallow-patterned InP (311)A substrates by chemical beam epitaxy. Temperature dependent photoluminescence (PL) reveals efficient carrier transfer from the adjacent dashlike QDs in the planar areas to the larger sidewall QDs resulting in well-distinguishable emission around 80K. The large high-energy shift of the PL from the sidewall QDs as a function of excitation power density is ascribed to the screening of the internal piezoelectric field. The linear polarization of the PL from the sidewall QDs is reversed compared to that of the quantum dashes in the planar areas due to the more symmetric shape and possible nonuniform strain in the sidewall QDs.

Ultrathin InAs and modulated InGaAs layers in GaAs grown by MOVPE studied by photomodulated reflectance spectroscopy

Photomodulated reflectance spectroscopy (PR) and X-ray diffraction (XRD) were used for the characterization of highly strained ultrathin InAs quantum wells and modulated InGaAs layers in GaAs grown by metal-organic vapor phase epitaxy (MOVPE). Structures were grown in AIXTRON 200 reactor at 500 °C on (1 0 0) oriented GaAs substrates by sequential growth of InAs and GaAs layers. Various PR spectral features corresponding to optical transitions between ground and excited states in the layers were identified by means of simulation of electronic states in these structures using nextnano 3 quantum simulator. Different models of InAs layer growth were used to explain both the XRD and PR data. Results show that the Gaussian distribution of In atoms within few monolayers gives the best fit for our MOVPE grown ultrathin InAs layers.

Fabrication of InP∕InAs∕InP core-multishell heterostructure nanowires by selective area metalorganic vapor phase epitaxy

We report the growth of InP∕InAs∕InP core-multishell nanowire arrays by selective area metalorganic vapor phase epitaxy. The core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. The precise control over nanowire growth direction and heterojunction formation enabled the successful fabrication of the nanostructure in which all three layers were epitaxially grown without the assistance of any catalyst. The grown nanowires were highly uniform, vertically oriented, and periodically aligned with controllable dimensions. 4K photoluminescence measurements confirmed the formation of strained InAs quantum well on InP (110) sidewalls and the well widths corresponding to the photoluminescence peaks were in good agreement with calculated values.

Interrelationships in the electronic and structural characteristics of strained InAs quantum well structures

Indium-arsenide (InAs)-based devices are promising for next generation electronic and optoelectronic applications. Improving these devices requires greater control of the InAs quantum well properties, which in part, are related to the strain induced from the substrate material, buffer layer thickness, barrier composition, doping, and the heterointerface. This report focuses on the latter and includes X-ray diffraction and Hall results from a statistical experimental design (SED), which focused on the growth sequence at the heterointerface and growth throughout the channel, and illuminates correlations between structural variations and the electronic properties in strained InAs quantum well structures produced by molecular beam epitaxy (MBE). This data suggest that as more antimony from the sublayer is incorporated in the InAs layer, a product of anion exchange between antimony surface atoms and ensuing arsenic flux atoms, the strain states vary along with InAs channel mobility.

Calculations of the electronic structure of strained InAs quantum dots in InP

We have calculated the electronic structure of InAs quantum dots embedded in InP as a function of size, using strain dependent eight-band k⋅p theory in the envelope function approximation. A realistic three-dimensional shape was used for the simulations and the piezoelectric polarization of the system was included. In order to avoid spurious solutions, an extra term was added to the Hamiltonian. Polarization dependent dipole matrix elements were calculated as well as the exciton binding energies. A comparison between measurements and calculated transition energies shows good agreement.

Toward a semiconductor-based terahertz nonlinear medium

The recent growth of interest in the terahertz (THz) region of the spectrum has spurred the development of new THz elements in analogy to elements used in optical and microwave systems. Nonlinear as well as linear elements are needed. In this study we explore theoretically the use of valence-subband nonparabolicity in strained p-type quantum wells (QWs) for third-harmonic generation. All fields—the fundamental as well as the harmonic—are polarized in the quantum-well plane, thus facilitating integration with lateral high-frequency electronic devices as well as for coupling to free-space fields. For strained InAs quantum wells, we find that the corresponding value of χ (3) can be as large as ∼10 −12 ( m/ V) 2 . The predicted values of χ (3), though not extremely large, are nevertheless in the range of those associated with intersubband transitions in the mid-infrared region of the spectrum.

Role of alloy spacer layers in non top-on-top vertical correlation in multistacked systems

We focus on the role of spacer alloy decomposition in the vertical correlation for a bilayer of strained InAs quantum wires, where the spacer layer is an immiscible alloy. We show how the surface morphology combined with the strongly inhomogeneous strain distribution favors a V-shaped partial demixing of the spacer layer. We also demonstrate that this decomposition has tangible consequences on the vertical organization when depositing a second wire layer. Different configurations can be obtained from perfect top-on-top, to perfect vertical anticorrelation, via all kinds of oblique correlation.

Terahertz nonlinear optics with strained p-type quantum wells

Valence-subband nonparabolicity is shown theoretically to lead to nonlinearities associated with terahertz third-harmonic generation in strained p -type quantum wells. For strained InAs quantum wells it is found that the corresponding value of chi((3)) can be as large as ~10(-12)(m/V)(2). The predicted values of chi((3)) are in the range of those associated with intersubband transitions in the mid-infrared region of the spectrum.

Tight-binding calculations of energy gaps in (001)-(InAs)n(InSb)m strained superlattices

Tight-binding calculations of electronic structures for (001)-(InAs)n(InSb)m strained layer superlattices are presented. The dependences of the superlattice band gap on the band offsets between InAs and InSb are examined for three different types of biaxial strains. It is found that the band gap depends strongly on the band offset, and that for m=1 the ordering lowers the band gap with respect to the random alloy. A comparison with the photoluminescence data for the energy gaps of (n×1) strained-layer superlattices is discussed. In addition, the electronic structures of strained InAs quantum wells are calculated, and interpretations are provided for the observed type-I to type-II band alignment transition at n=5 in a quantum well formed by (n×1) strained layer superlattices and AlSb barriers. Changes of energy gaps with layer thicknesses in strained layer superlattices with n=m and n=8−m are also studied.

Photo-and electroluminescence in the 1.3-µm wavelength range from quantum-dot structures grown on GaAs substrates

A method is proposed to increase the emission wavelength from structures grown on GaAs substrates by inserting a strained InAs quantum dot array into an external InGaAs quantum well. The dependence of the luminescence peak position on the active region design was investigated for structures grown by this method. Room-temperature photo-and electroluminescence spectra in the 1.3-µm wavelength range are compared.

Size distribution of coherently strained InAs quantum dots

The influence of the InAs coverage on the size and density of coherently strained InAs islands was investigated. At moderate InAs coverages the photoluminescence signal reflects the Gaussian size distribution of small coherently strained islands. However, before the coherently strained islands transform into dislocated ones the Gaussian line shape of their photoluminescence signal changes and a narrow peak appears on the low-energy tail. We attribute this change to an accumulation of coherently strained islands at a maximum size before dislocated island transformation occurs. Effects of luminescence from dislocated islands, size-dependent relaxation processes, capture efficiencies, and dot-dot coupling are also discussed. However, our calculations and the magnetophotoluminescence, as well as the photovoltage experiments, confirm our interpretation of a size accumulation process of coherently strained islands.