Interfacial Misfit Research Articles

Integration of an InSb photodetector on Si via heteroepitaxy for the mid-infrared wavelength region

In this study, InSb p-i-n photodetectors with In0.82Al0.18Sb barrier layers were grown on a (100) 6° offcut Si substrate by heteroepitaxy via an AlSb/GaSb buffer. Based on an interfacial misfit array growth mode, the dislocations at the GaSb/Si and InSb/AlSb interfaces accommodated the lattice mismatch. The In0.82Al0.18Sb barrier layer increased the 77 K R0A of the detector. From 180 K to 300 K, the generation-recombination mechanism dominated the dark current generation in the detector and surface leakage became dominant below 120 K. The detector exhibited a 77 K responsivity of 0.475 A/W and a Johnson-noise-limited detectivity of 3.08 × 109 cmHz1/2W-1 at 5.3 µm.

Vacancy assisted He-interstitial clustering and their elemental interaction at fcc-bcc semicoherent metallic interface

Cu-Nb layered nanocomposite system can be considered as a prototype system to investigate stability of the fcc-bcc semicoherent metallic interfaces. Theoretical simulations based on density functional theory have been performed in order to investigate the stability of different defects in such interfaces. The calculations find the interfacial misfit dislocation intersections as the preferred site for defects including a vacancy, He-interstitial, and a vacancy-He complex in good agreement with previous works. Our results suggest that the presence of a metallic vacancy may act as a sink for defect and favour the migration of He interstitials leading to their aggregation at the interface. The potential capability of the vacancy to accommodate He atoms was also predicted with a higher affinity towards Nb. This aggregation of He atoms is driven by local density of electron and strain in a region in the neighbourhood of Nb. Finally, we propose a plausible picture of defect energetics in the vicinity of the interface based on the Voronoi volume and Bader’s charge analysis. This analysis may replace the conventional methods used for surface energetics mapping which are extremely tedious for such large systems.

Size effect on the plastic deformation of pre-void Ni/Ni3Al interface under uniaxial tension: A molecular dynamics simulation

In this paper, the plastic deformation mechanism of pre-void Ni/Ni3Al interface alloy under tensile load dependent on the size of pre-existing void in Ni/Ni3Al interface is investigated by using molecular dynamics simulations with Embedded Atom Method (EAM) potential. It is interesting that for the special case of infinitely long cylindrical voids, it is found that the pre-void Ni/Ni3Al interface structures with relatively smaller radius produce higher yield stresses than the void-free sample, as the smaller voids in interface help to disperse the local energy induced by the interface misfit in elastic tension. The competition between the initial edge dislocation formed from lattice misfit and Shockley partial nucleated from the pre-void contributes to triggering the varying dislocation nucleation and plastic deformation patterns. And it is found that the propagations of the slip bands emitted from Stair-rod dislocation and stacking faults generated from Shockley partial are the main plastic deformation mechanism. Moreover, obvious temperature effects on the stress-strain curves and the Young’s modulus are found in the Ni/Ni3Al interface alloy with a constant pre-void radius.

New type of γ′ phase in Ni based single crystal superalloys: Its formation mechanism and strengthening effect

New type of γ′-precipitate in Ni-(6-8)Al-(7-12)Mo-4.5Ta-1.5Re (weight%) single-crystal superalloys and its effect on mechanical properties have been investigated. The phase exhibits a rattan form from cross-sectional observation while a curved thin film in stereoscopic structure. Its density is strongly linked to Al and Mo contents and holding time of solid solution. Its formation arises as a result of i) the overlap of γ′-precipitate and ii) the subsequent interface migration; the former is caused by the mismatch of γ-γ′ periodicity, which is inherited from the congruent ordering and spinodal decomposition independently occurring in different regions; the latter is driven from the chemical potential difference between γ-ribbon and γ′-precipitate induced by interface curvature and misfit stress. The γ′-rattan improves room temperature tensile properties through changing the slip lines and inhibiting the crack growth, which is ascribed to the change in the stress field of γ-γ′ structure.

Monolithic Integration of InSb Photodetector on Silicon for Mid-Infrared Silicon Photonics

The InSb photodetector on a Si substrate acts as a signal receiver for the mid-infrared silicon photonics application to overcome the limitation of group IV semiconductors. In this paper, we demonstrated an InSb p–i–n photodetector with an InAlSb barrier layer grown on (100) silicon substrates via a GaAs/Ge buffer by molecular beam epitaxy. The lattice mismatch between InSb and GaAs was accommodated by an interfacial misfit array. The 50% cutoff detectable wavelength of this detector increased from 5.7 μm at 80 K to 6.3 μm at 200 K. An 80 K detectivity of 8.8 × 109 cmHz1/2 W–1 at 5.3 μm was achieved with a quantum efficiency of 16.3%. The dark current generating mechanism of this detector is both generation–recombination and surface leakage above 140 K, while it is only surface leakage from 120 to 40 K.

Direct growth of InAs/GaSb type II superlattice photodiodes on silicon substrates

p-i-n InAs/GaSb type II superlattice photodiodes were directly grown on silicon substrates. The superlattice structures were grown monolithically on miscut Si substrates via a 10 nm AlSb nucleation layer. Interfacial misfit array technique was used to accommodate the large lattice mismatch between III-Sb epi-layers and Si. Atomic force microscopy and X-ray diffraction measurements revealed degraded material quality of type II superlattices grown on Si, compared with the sample grown on GaAs. Photoluminescence characterization indicates comparable optical properties with about 39% deduction of peak intensity. Dark current measurements were also used to study the electrical properties of the samples.

Growth and characterization of InSb on (1 0 0) Si for mid-infrared application

Monolithic integration of InSb on (100) Si is a practical approach to realizing on-chip mid-infrared photonic devices. An InSb layer was grown on a (100) Si substrate using an AlSb/GaSb buffer containing InSb quantum dots (QDs). The growth process for the buffer involved the growth of GaSb on Si using an interfacial misfit array, followed by InSb QDs on AlSb to decrease the density of microtwins. InSb layers were separately grown on AlSb and GaSb surfaces to compare the effect of different interfacial misfit arrays. The samples were characterized using transmission electron microscopy and X-ray diffraction to determine the structural properties of the buffer and InSb layers. The InSb on the AlSb sample exhibited higher crystal quality than the InSb on GaSb sample due to a more favorable arrangement of interfacial misfit dislocations. Hall measurements of unintentionally doped InSb layers demonstrated a higher carrier mobility in the InSb on the AlSb sample than in InSb on GaSb. Growing InSb on AlSb also improved the photoresponsivity of InSb as a photoconductor on Si.

Performance evaluation of InAs/GaSb superlattice photodetector grown on GaAs substrate using AlSb interfacial misfit array

We report on the growth and opto-electronic characterization of type-II InAs/GaSb superlattice (SL) mid-wavelength infrared pin photodetector grown on a GaAs substrate. AlSb interfacial misfit array was employed at the GaAs buffer/GaSb epilayer interface to reduce the dislocation density of the SL structure grown on the lattice mismatched GaAs substrate. Optical and electrical performance of this sample (SL-GaAs) were then compared with the reference sample of the same structure grown on a GaSb substrate (SL-GaSb). At 80 K, the dark current density and the detectivity values of the pin photodetectors were recorded as 5.40 × 10−3 A cm−2 and 2.34 × 1010 cm Hz0.5 W−1 for the SL-GaAs and 9.50 × 10−4 A cm−2 and 4.70 × 1010 cm Hz0.5 W−1 for the SL-GaSb, respectively.

Molecular dynamics studies of InGaN growth on nonpolar (112¯0) GaN surfaces

We have performed direct molecular dynamics (MD) simulations of heteroepitaxial vapor deposition of $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$ films on nonpolar $(11\overline{2}0)$ wurtzite-GaN surfaces to investigate strain relaxation by misfit-dislocation formation. The simulated growth is conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN substrate. We apply time-and-position-dependent boundary constraints to affect the appropriate environments for the vapor phase, the near-surface solid phase, and the bulklike regions of the growing layer. The simulations employ a newly optimized Stillinger-Weber In-Ga-N system interatomic potential wherein multiple binary and ternary structures are included in the underlying density-functional theory and experimental training sets to improve the treatment of the In-Ga-N related interactions. To examine the effect of growth conditions, we study a matrix of 63 different MD-growth simulations spanning seven $\mathrm{I}{\mathrm{n}}_{x}\mathrm{G}{\mathrm{a}}_{1\ensuremath{-}x}\mathrm{N}$-alloy compositions ranging from $x=0.0$ to $x=0.8$ and nine growth temperatures above half the simulated melt temperature. We found a composition dependent temperature range where all kinetically trapped defects were eliminated, leaving only quasiequilibrium misfit and threading dislocations present in the simulated films. Based on the MD results obtained in this temperature range, we observe the formation of interfacial misfit and threading dislocation arrays with morphologies strikingly close to those seen in experiments. In addition, we compare the MD-observed thickness-dependent onset of misfit-dislocation formation to continuum-elasticity-theory models of the critical thickness and find reasonably good agreement. Finally, we use the three-dimensional atomistic details uniquely available in the MD-growth histories to directly observe the nucleation of dislocations at surface pits in the evolving free surface.

Preferential nucleation, guiding, and blocking of self-propelled droplets by dislocations

Lattice-mismatched layers of GaAs/InGaAs are grown on GaAs(001) using molecular beam epitaxy and subsequently heated in vacuum while the surface is imaged in situ using low-energy electron microscopy, in order to study (i) the nucleation of group-III droplets formed as a result of noncongruent sublimation and (ii) the dynamics of these self-propelled droplets as they navigate the surface. It is found that the interfacial misfit dislocation network not only influences the nucleation sites of droplets, but also exerts unusual steering power over their subsequent motion. Atypical droplet flow patterns including 90° and 180° turns are found. The directions of these dislocations-guided droplets are qualitatively explained in terms of in-plane and out-of-plane stress fields associated with the buried dislocations and the driving forces due to chemical potential and stress gradients typical of Marangoni flow. The findings would benefit processes and devices that employ droplets as catalysts or active structures such as droplet epitaxy of quantum nanostructures, vapor-liquid-solid growth of nanowires, or the fabrication of self-integrated circuits.

Nondestructive Evaluation of Strain-Induced Phase Transformation and Damage Accumulation in Austenitic Stainless Steel Subjected to Cyclic Loading

Strain-induced phase transformation and damage accumulation in austenitic stainless steel subjected to cyclic loading were investigated by nondestructive evaluation. The cyclic loading test was performed at various strain amplitudes at the same strain rate. The volume fraction of the strain-induced phase transformation (α′-martensite) was determined by ferrite scope and magnetic coercivity measurement. The damage accumulation and microstructure of cyclic loading specimens were characterized by microstructural observation. The cyclic hardening and cyclic softening behavior are discussed in terms of the generation of strain-induced martensite phases and a dislocation substructure at each strain amplitude. The volume fraction of the strain-induced phase increased with the strain amplitude. The increase in α′-martensite was evaluated by measuring the ultrasonic nonlinearity parameter. The presence of α′-martensite is sufficient to distort the austenitic matrix due to an interface misfit between the austenite matrix and α′-martensite, resulting in wave distortion of the longitudinal wave. From this wave distortion, super-harmonics may be generated with nucleation of the strain-induced martensite, a process that strongly depends on the strain amplitude.

GaSb solar cells grown on GaAs via interfacial misfit arrays for use in the III-Sb multi-junction cell

Growth of GaSb with low threading dislocation density directly on GaAs may be possible with the strategic strain relaxation of interfacial misfit arrays. This creates an opportunity for a multi-junction solar cell with access to a wide range of well-developed direct bandgap materials. Multi-junction cells with a single layer of GaSb/GaAs interfacial misfit arrays could achieve higher efficiency than state-of-the-art inverted metamorphic multi-junction cells while forgoing the need for costly compositionally graded buffer layers. To develop this technology, GaSb single junction cells were grown via molecular beam epitaxy on both GaSb and GaAs substrates to compare homoepitaxial and heteroepitaxial GaSb device results. The GaSb-on-GaSb cell had an AM1.5g efficiency of 5.5% and a 44-sun AM1.5d efficiency of 8.9%. The GaSb-on-GaAs cell was 1.0% efficient under AM1.5g and 4.5% at 44 suns. The lower performance of the heteroepitaxial cell was due to low minority carrier Shockley-Read-Hall lifetimes and bulk shunting caused by defects related to the mismatched growth. A physics-based device simulator was used to create an inverted triple-junction GaInP/GaAs/GaSb model. The model predicted that, with current GaSb-on-GaAs material quality, the not-current-matched, proof-of-concept cell would provide 0.5% absolute efficiency gain over a tandem GaInP/GaAs cell at 1 sun and 2.5% gain at 44 suns, indicating that the effectiveness of the GaSb junction was a function of concentration.

Designing nickel base alloys for microstructural stability through low γ-γ′ interfacial energy and lattice misfit

An extended stability alloy design strategy for multicomponent γ-γ′ nickel-base alloys with near-zero lattice misfit and as low as possible interfacial energy was investigated by isothermal annealing of two experimental alloys at 900°C for times up to 256h. The coarsening behavior of the spherical γ′ precipitates and the phase compositions determined by atom probe tomography were utilized to exploit a modified Lifshitz-Slyozov-Wagner relationship to estimate the interfacial energies. The estimated interfacial energies are much lower than predicted by a CALPHAD-based software as well as those typically reported for multicomponent γ-γ′ nickel alloys. Despite successfully minimizing the interfacial energy and γ-γ′ lattice misfit, these factors alone were not sufficient to impart high temperature extended stability through reduced coarsening kinetics.

A novel interface strengthening layer: Nanoscale AuCu super-structure formed during Au80Sn20/Cu rapid solidification soldering process

Phase composition and orientation of intermetallic compounds layers determine the functional and mechanical properties of solder joints. In this paper, interfacial reaction and strengthening mechanism of Au80Sn20/Cu joint by rapid solidification reflow soldering were studied. The Au80Sn20/Cu solder joint by rapid solidification reflow soldering exhibit a superior shear property, and the shear strength reaches up to 90MPa. It is found that a new nanoscale AuCu super-structure formed in the interfacial intermetallic compounds layer, which is coherent with the [001] Cu substrate. The orientation relationship of Cu matrix/interfacial intermetallic compounds is determined to be001Cu∥001AuCu∥2¯42¯3AuCu5Sn and200Cu∥200AuCu∥101¯0AuCu5Sn. Nanoscale AuCu super-structure influences the interface slip direction and provides interface misfit dislocation, hinder the dislocation movement, lead to the interface strengthening effect. Our finding on nanoscale AuCu super-structure formed during Au80Sn20/Cu soldering process not only sheds light on future research direction but also provides practical guidance to the engineers in solder industry.

Optimization of the interfacial misfit array growth mode of GaSb epilayers on GaAs substrate

The growth of undoped GaSb epilayers on GaAs (0 0 1) substrates with 2° offcut towards 〈1 1 0〉, by molecular beam epitaxy system (MBE) at low growth temperature is reported. The strain due to the lattice mismatch of 7.78% is relieved spontaneously at the interface by using interfacial misfit array (IMF) growth mode. Three approaches of this technique are investigated. The difference consists in the steps after the growth of GaAs buffer layer. These steps are the desorption of arsenic from the GaAs surface, and the cooling down to the growth temperature, under or without antimony flux. The X-ray analysis and the transmission electron microscopy point out that desorption of arsenic followed by the substrate temperature decreasing under no group V flux leads to the best structural and crystallographic properties in the GaSb layer. It is found that the 2 µm-thick GaSb is 99.8% relaxed, and that the strain is relieved by the formation of a periodic array of 90° pure-edge dislocations along the [1 1 0] direction with a periodicity of 5.6 nm.

Colloidal Silicon–Germanium Nanorod Heterostructures

Colloidal nanorods with axial Si and Ge heterojunction segments were produced by solution–liquid–solid (SLS) growth using Sn as a seed metal and trisilane and diphenylgermane as Si and Ge reactants. The low solubility of Si and Ge in Sn helps to generate abrupt Si–Ge heterojunction interfaces. To control the composition of the nanorods, it was also necessary to limit an undesired side reaction between the Ge reaction byproduct tetraphenylgermane and trisilane. High-resolution transmission electron microscopy reveals that the Si–Ge interfaces are epitaxial, which gives rise to a significant amount of bond strain resulting in interfacial misfit dislocations that nucleate stacking faults in the nanorods.

Atomically flat and uniform relaxed III\u2013V epitaxial films on silicon substrate for heterogeneous and hybrid integration

The integration of III-V semiconductors on silicon (Si) substrate has been an active field of research for more than 30 years. Various approaches have been investigated, including growth of buffer layers to accommodate the lattice mismatch between the Si substrate and the III-V layer, Si- or Ge-on-insulator, epitaxial transfer methods, epitaxial lateral overgrowth, aspect-ratio-trapping techniques, and interfacial misfit array formation. However, manufacturing standards have not been met and significant levels of remaining defectivity, high cost, and complex integration schemes have hampered large scale commercial impact. Here we report on low cost, relaxed, atomically smooth, and surface undulation free lattice mismatched III-V epitaxial films grown in wide-fields of micrometer size on 300 mm Si(100) and (111) substrates. The crystallographic quality of the epitaxial film beyond a few atomic layers from the Si substrate is accomplished by formation of an interfacial misfit array. This development may enable future platforms of integrated low-power logic, power amplifiers, voltage controllers, and optoelectronics components.

Alternative misfit dislocations pattern in semi-coherent FCC {100} interfaces

The character of interface misfit dislocations is determined according to interface crystallography and minimization of interface energy, which includes coherent interface energy and dislocation line energy. The core energy of dislocations is generally ignored in such analysis. In this work, we demonstrate that the core energy of misfit dislocations is dependent on the mechanical and thermal loading condition, and ultimately determines the nature of interface misfit dislocation patterns (MDP). Employing atomistic simulations with empirical interatomic potentials, we show the transformation of conventional MDP consisting of a/2<110> dislocation into an alternative MDP consisting of mixed a<100> and a/2<110> dislocations under elevated temperatures and/or normal-to-interface tensile stresses. Although a<100> type dislocations typically have greater line energy in bulk, molecular statics/dynamics calculations show that a<100> type misfit dislocations are preferred over a/2<110> type under elevated temperatures and/or normal-to-interface tensile stresses due to their reduced core energy. In addition, we found that the a<100> dislocations possess significantly reduced vacancy formation energies compared to the a/2<110> dislocations. The potential application of this unique property of the alternative dislocation pattern for nanoscale multilayered composite as a functional material is discussed.

Growth and characterization of high quality N-type GaSb/GaAs heterostructure by IMF growth mode using MOCVD for low power application

In this study, we demonstrate the growth of a 150-nm-thick GaSb layer on a GaAs substrate with excellent film quality using the interfacial misfit dislocation growth mode by the Metal–Organic Chemical Vapor Deposition technique. The n-type GaSb epilayer grown on the GaAs substrate has a low threading dislocation density of 3.2 × 106 cm−2 and a surface roughness of approximately 0.8 nm. A high carrier mobility up to 4600 cm2 V−1 s−1 with a carrier concentration of 1.2 × 1017 cm−3 is achieved in this study. The fabricated Al2O3/GaSb/GaAs MOSCAP demonstrated excellent capacitance–voltage (C–V) characteristics with a small frequency dispersion of approximately 2.8%/decade. The results demonstrate the potential of high-mobility Sb-based materials on GaAs for p-type channel CMOS applications in the future.

Effect of in situ annealing on the structural and electrical properties and infrared photodetection of III-Sb on GaAs using interfacial misfit array

Abstract This work presents the effects of in situ thermal annealing under antimony overpressure on the structural, electrical, and optical properties of III-Sb (GaSb and InSb) grown on (100) GaAs using an interfacial misfit array to accommodate the lattice mismatch. Both the sample growth and the in situ thermal annealing were carried out in the in the molecular beam epitaxy system, and the temperature of the as-grown sample was increased to exceed its growth temperature during the annealing. X-ray diffraction demonstrates nearly fully relaxed as-grown and annealed III-Sb layers. The optimal annealing temperatures and durations are for 590 °C, 5 min for GaSb and 420 °C, 15 min for InSb, respectively. In situ annealing decreased the surface roughness of the III-Sb layers. X-ray reciprocal space mapping and transmission electron microscopy observation showed stable interfacial misfit arrays, and no interfacial diffusion occurred in the annealed III-Sb layers. A Hall measurement of unintentionally doped III-Sb layers showed greater carrier mobility and a lower carrier concentration in the annealed samples at both 77 and 300 K. In situ annealing improved the photoresponsivity of GaSb and InSb photoconductors grown on GaAs in the near- and mid-infrared ranges, respectively.