Lattice Matching Condition Research Articles

Growth of Lattice-Matched ZnTeSe Alloys on (100) and (211)B GaSb

A key issue with the current HgCdTe/Si system is the high dislocation density due to the large mismatch between HgCdTe and Si. An alternative system that has superior lattice matching is HgCdSe/GaSb. A buffer layer to mitigate issues with direct nucleation of HgCdSe on GaSb is ZnTe1−xSex. We have performed preliminary studies into the growth of lattice-matched ZnTe1−xSex on both (100) and (211)B GaSb. The effects of substrate orientation, substrate temperature, and growth conditions on the morphology and crystallography of ZnTe0.99Se0.01 alloys were investigated. The lattice-matching condition yielded minimum root-mean-square (rms) roughness of 1.1 nm, x-ray rocking curve full-width at half-maximum (FWHM) value of ~29 arcsec, and density of nonradiative defects of mid-105 cm−2 as measured by imaging photoluminescence.

Strain compensation in AlInN/GaN multilayers on GaN substrates: Application to the realization of defect-free Bragg reflectors

We report on the growth conditions of AlInN layers grown on free-standing GaN substrates. We found that an average indium content of ∼20% is needed to obtain defect-free AlInN/GaN multilayers. This is larger than the commonly accepted value of 18% for lattice-matched condition. A model where tensile strain at the GaN/AlInN interface is induced by indium surface segregation occurring in AlInN layers is proposed to explain this discrepancy. A high In/Al flux ratio is shown to reduce this effect and allowed obtaining a defect-free AlInN/GaN Bragg reflector with a peak reflectivity of 99.6% suitable for vertical cavity light emitting devices.

Refractive index and dielectric constants of lattice matched and mismatched CdxZn1−xSeyTe1−y quaternary alloys

We report on a study of optical properties, namely the refractive index and high-frequency and static dielectric constants of zinc-blende CdxZn1−xSeyTe1−y under conditions of lattice matching and lattice mismatching to ZnTe substrates. The calculations are mainly based on the pseudopotential approach under a virtual crystal approximation. Our results show that the CdxZn1−xSeyTe1−y lattice matched to ZnTe is a direct band-gap semiconductor for all possible values of x and y (0 ≤x≤1, 0≤y≤0.879). The studied features are found to be strongly dependent on the lattice mismatch percentage. The present investigation provides more opportunities to obtain diverse refractive indices and dielectric constants, while still controlling the composition parameters (x and y) and/or the lattice mismatch percentage.

On the material parameters of some useful quaternary compounds relevant to optoelectronic device design

Studies of some quaternary compounds showing lattice matching condition on various substrates suitable for device design in various wavelength regions have been reported here. The compositional dependence of lowest energy band gap, dielectric constant, coefficient of thermal expansion, temperature and pressure dependence of lowest band gap energy, etc. of these compounds have been presented and finally proper concentrations suitable for device design under lattice matching condition have been mentioned.

M -plane (101̱0) InN heteroepitaxied on (100)-γ-LiAlO2 substrate: Growth orientation control and characterization of structural and optical anisotropy

Heteroepitaxial growth of m-plane (101̱0) InN film on (100)-γ-LiAlO2 (LAO) substrate has been realized by plasma-assisted molecular-beam epitaxy. Surface treatment of LAO substrate plays an important role in controlling the resultant phase and purity of m-plane InN. X-ray diffraction, reflection high-energy electron diffraction, electron back scatter diffraction, and transmission electron microscopy (TEM) studies revealed formation of pure m-plane InN film using substrate preannealed at 800 °C but without any nitridation. In contrast, using substrate with nitridation but otherwise identical pretreatment and growth conditions, c-plane (0001) InN columnar structure was grown, instead of m-plane InN film. Structural anisotropy of the m-plane InN epitaxied on LAO is attributed to the I1 type base-plane stacking faults according to the modified Williamson–Hall and TEM analyses. A rectangular-to-rectangular atomic stacking sequence and a commensurately lattice-matched condition in epitaxial direction of [12̱10]InN∥[001]LAO with a small misfit strain of ∼0.2% are proposed to realize this heteroepitaxy. Angle-dependent polarized UV-Raman spectra showed that all the InN phonon modes follow Raman selection rule well. Strong polarization anisotropy of photoluminescence (PL) emission located at ∼0.63 eV was observed, as evidenced by a high polarization degree of 87% of the m-plane InN determined by infrared polarized PL spectroscopy.

Lattice-Latching Effect in Metalorganic Vapor Phase Epitaxy Growth of InGaAsN Film Lattice-Matched to Bulk InGaAs Substrate

The effects of lattice mismatch between an InzGa1-zAs bulk substrate and an InxGa1-xAs1-yNy epilayer on the incorporation kinetics of N (y) and In (x) were investigated. Compositions (x,y) were revealed to be pinned by the substrate to those satisfying lattice-matching conditions. With decreasing In (z) content in the substrate, the incorporation of N is spontaneously enhanced. On the other hand, the In content of the layer is reduced to decrese the deformation energy due to the lattice mismatch. On the basis of our results, thick InxGa1-xAs1-yNy (0.289 < x < 0.312 and 0.009 < y < 0.014) layers exhibiting photoluminescence in the wavelength range of 1.3–1.55 µm were observed to grow owing to the “lattice-latching” effect.

Depth-resolved analysis of spontaneous phase separation in the growth of lattice-matched AlInN

We report the detection of phase separation of an Al1−xInxN/GaN heterojunction grown close to lattice-matched conditions (x ∼ 0.18) by means of Rutherford backscattering spectrometry in channelling geometry and high-resolution x-ray diffraction. An initial pseudomorphic growth of the film was found, with good single crystalline quality, the nominal composition and very low strain state. After ∼50 nm, a critical thickness is reached at which the InN molar fraction of the films drops to ∼15% and at the same time the single crystalline quality of the films degrade drastically. This spontaneous effect cannot be ascribed to strain relaxation mechanisms since both techniques show a good single crystalline growth of the ternary under lattice matched conditions.

Effect of lattice mismatch on gate lag in high quality InAlN/AlN/GaN HFET structures

AbstractGrown lattice matched to GaN, InAlN‐based heterojunction field effect transistors (HFETs) are promising due to the relatively large band discontinuity at the interface and lack of misfit strain. Despite the recent progress in the growth, there still exists some questions as to the true lattice matching condition of InAlN to GaN due to discrepancies in the value of the lattice parameters of the InN binary, as well as the literature value of the InAlN bowing parameters. In order to address this, we used the gate lag as a supplementary measurement to verify lattice matching to the underlying GaN, as strain‐free layers would not have piezoelectric charge at the surface, which would be one source of lag. We observe very low lag for a nearly lattice matched barrier, and a marked increase as the composition deviates from the lattice matched condition. Additionally, FETs fabricated on a nearly matched layer boast a maximum drain current of over 1.5 and ∼2.0 A/mm and transconductances of ∼275 and ∼300 mS/mm at DC and in pulsed modes, respectively, and a cutoff frequency of 15.9 GHz (an fT*LG product of 10.3) for a gate length of 0.65 µm.

Suppression of phase separation in InGaN layers grown on lattice-matched ZnO substrates

Sapphire and SiC are typical substrates used for GaN growth. However, they are non-native substrates and result in highly defective materials. The use of ZnO substrates can result in perfect lattice-matched conditions for 22% indium InGaN layers, which have been found to suppress phase separation compared to the same growths on sapphire. InGaN layers were grown on standard (0 0 0 2) GaN template/sapphire and (0 0 0 1) ZnO substrates by metalorganic chemical vapor deposition. These two substrates exhibited two distinct states of strain relaxation, which have direct effects on phase separation. InGaN with 32% indium exhibited phase separation when grown on sapphire. Sapphire samples were compared with corresponding growths on ZnO, which showed no evidence of phase separation with indium content as high as 43%. Additional studies in Si-doping of InGaN films also strongly induced phase separation in the films on sapphire compared with those on ZnO. High-resolution transmission electron microscopy results showed perfectly matched crystals at the GaN buffer/ZnO interface. This implied that InGaN with high indium content may stay completely strained on a thin GaN buffer. This method of lattice matching InGaN on ZnO offers a new approach to grow efficient emitters.

Electronics and Photonics Integration on Non-Crystalline Substrates via Nanoheteroepitaxy

The ability to grow dissimilar materials with large lattice mismatches on a single substrate removes the integration related constraints of incorporating photonics with electronics. We review our recent nanoheteroepitaxy efforts on the epitaxial growth of bridged InP NWs between two vertical, (111)-oriented Si surfaces by forming connections during the NW growth facilitating their direct electrical probing via Si electrodes and a new method of synthesizing III-V NWs on a non-single crystalline surface that directly relaxes any lattice matching conditions. The current-voltage behavior with temperature and the resulting photo-enhanced thermal failure is also discussed.

(Al,In)N layers and (Al,In)N/GaN heterostructures grown by plasma-assisted molecular beam epitaxy on6H-SiC(0001)

We study the properties of (Al,In)N layers and (Al,In)N/GaN heterostructures grown on $6H\text{-SiC}(0001)$ by plasma-assisted molecular beam epitaxy. The (Al,In)N films are deposited on a GaN buffer layer. A growth temperature of $500\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ and above results in low In contents which give rise to cracks due to the large tensile strain experienced from the underlying GaN buffer layer. In addition, these layers exhibit strong phase separation leading to inhomogeneous In composition and rough surfaces. In contrast, samples with homogeneous and well-controlled In-contents between 10%--30% are reproducibly obtained in the temperature range of $250--350\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. Surprisingly, nominally lattice-matched layers with an In content of 17%--18% also exhibit cracks. Symmetric $\ensuremath{\omega}\ensuremath{-}2\ensuremath{\theta}$ x-ray diffraction scans and reciprocal space maps reveal the presence of a strain gradient in these layers despite the apparently lattice-matched conditions. Transmission electron microscopy indicates that these cracks are the result of tensile stresses induced by crystallite coalescence and grain-boundary formation. This mechanism can be counteracted by augmenting the adatom mobility through increasing the growth temperature and the N flux. However, phase separation sets an upper limit on the growth temperature and a moderate increase to $350--400\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ is sufficient to obtain crack-free and homogeneous (Al,In)N layers. The results of our growth experiments lead to a phase diagram which shows the optimum growth window for (Al,In)N layers. By choosing the growth conditions within this window, we are able to obtain crack-free ${\text{Al}}_{0.82}{\text{In}}_{0.18}\text{N}/\text{GaN}$ multilayers with abrupt interfaces.

Low-Threshold 1.3-$\mu$m GaInNAs Quantum-Well Lasers Using Quaternary-Barrier Structures

GaInNAs quaternary-barrier structures, where indium is incorporated to achieve the lattice-matched condition, have been employed for 1.3-m GaInNAs-GaAs single- (SQW) and triple-quantum-well (TQW) lasers. Compared to a GaNAs ternary-barrier structure, photoluminescence results from the quaternary-barrier sample show improved optical properties. Threshold current densities have been achieved with the lowest values of 150 and 529 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for GaInNAs SQW and TQW lasers at room temperature, respectively.

Role of substrate bias on the magnetic properties and microstructure of CoCrPt:SiO2 perpendicular recording media

The role of substrate bias during the sputter deposition of various layers of double-layered CoCrPt−SiO2 perpendicular recording media has been investigated in order to understand the physical mechanisms behind the various effects observed. Perpendicular recording media with dual Ru intermediate layers were investigated using several magnetic and microstructural characterization techniques. It was observed that, in general, the application of a bias voltage during the deposition of the seedlayer (Ta) and the first intermediate layer (Ru) is helpful in reducing the c-axis dispersion of the recording layer. For the other layers, application of bias voltage leads to deterioration in the magnetic properties. It was also observed that the application of a bias voltage during the deposition of the first intermediate layer (especially Ru) may not enhance the preferred growth of Ru hexagonal-close-packed (00.2) planes parallel to the disk surface, as predicted before. However, the bias voltage on the Ru layer still reduces the c-axis dispersion of the magnetic layer. From the omega-offset x-ray diffraction investigations, it is estimated that the lattice parameter “a” of the Ru layer is reduced slightly with bias voltage, which could probably lead to a reduction in the lattice mismatch between the Ru layer and Co-alloy layer. Bias conditions also could lead to improved interface condition. Such an improvement in the lattice matching or interface conditions could probably be the cause of the reduction of c-axis dispersion of the recording layer.

Energy band gaps for the GaxIn1−xAsyP1−y alloys lattice matched to different substrates

Abstract A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the GaxIn1−xAsyP1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all y compositions whatever the lattice matching to the substrates of interest. The ( Γ → Γ ) band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of y and the substrate, GaxIn1−xAsyP1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties.

Deep donor-acceptor pair recombination in InGaAs-based heterostructures grown on InP substrates

We are investigating a series of lattice-matched InxGa1−xAs∕InAsyP1−y double heterostructures with indium concentrations ranging between x=0.53 and x=0.78. The double heterostructures incorporating indium-rich alloys (x&amp;gt;0.53) experience lattice mismatch relative to the InP substrate. Previous work has produced convincing but indirect evidence that the distribution of defect levels in the InxGa1−xAs changes dramatically when the epistructure deviates from the lattice-matched condition. In particular, deep midgap states appear to give way to shallower near-band-edge states with increasing mismatch. Here, we report sub-band-gap photoluminescence measurements that explore these changes directly. We observe a broad low-energy peak in the spectra of the lattice-matched and nearly lattice-matched epistructures that is not present in the more mismatched case. The sub-band-gap emission blueshifts and grows superlinearly with photoexcitation up to and exceeding 1000W∕cm2. This unusual behavior is attributed to transitions between ordinary acceptor levels and deep, defect-related donorlike states. We find no evidence for the shallower defect states that we expected to arise with increasing lattice mismatch.

Conformational studies of self-organized regioregular poly(3-dodecylthiophene)s using non-contact atomic force microscopy in ultra high vacuum condition

Conformations of one of the variations of π-conjugated poly-alkylthiophene, poly(3-dodecylthiophene)s (P3DDT)s on the surface in ultra high vacuum (UHV) were investigated by non-contact atomic force microscopy (NC-AFM) operated by frequency-modulation mode (FM-mode). From individual molecules to several multi-layered ones, polymer chains on the surface were clearly resolved on conducting highly oriented pyrolytic graphite (HOPG) substrates and insulating mica ones, respectively. Solvent evaporation was found to have two stages, which influenced the diffusion, ordering, and adhesion processes of polymer chains on the substrate. To keep the ordered conformations of deposited polymer chains when they are transferred from ambient condition to UHV, these evaporation processes should be carefully considered. The initial conformation of polymers on the substrate was found to depend strongly on the lattice matching conditions and interactions between polymers and substrates. Formations of stripe-like structures of P3DDT polymers were found on the mica substrates, which is promising for device application.

Effect of Induced Strain Due to Lattice Mismatch between MgyZn1-yS Cladding Layers and CdxZn1-xS/ZnS Quantum Wells on Effective Band Gap Energy in CdxZn1-xS/ZnS/MgyZn1-yS Separate-Confinement Heterostructures

We calculate the effect of the induced strain due to lattice mismatch between CdxZn1-xS/ZnS quantum wells (QWs) and MgyZn1-yS cladding layers on the effective band gap energy in CdxZn1-xS/ZnS/MgyZn1-yS separate-confinement heterostructures (SCHs). The effective band gap energy in the CdxZn1-xS/ZnS/MgyZn1-yS SCHs increases with increasing Mg content (y) for wider wells. The variation in effective band gap energy reflects the peak energy of optical gain spectra. The effect of the induced strain due to MgyZn1-yS cladding layers on the threshold carrier concentration for the production of a positive optical gain is very weak. The lattice-matching condition for the MgyZn1-yS cladding layers with respect to the CdxZn1-xS/ZnS MQWs is estimated. The induced strain due to the lattice mismatch between MgyZn1-yS cladding layers and CdxZn1-xS/ZnS MQWs is suppressed by adjusting y.

In depth study of the compensation in annealed heavily carbon doped GaAs

Heavily C-doped GaAs epitaxial layers with holes concentrations ranging from 1019 to 1.6×1020cm−3 have been grown by metal organic vapour phase epitaxy (MOVPE) using CCl4 as C-growth precursor. The carbon doping characteristics of GaAs epilayers have been investigated by optimizing the V/III ratio and the growth temperature. Additional informations have been extracted from the evolution of the in situ reflectivity signal during the growth of GaAs:C. The appearance of discernible oscillations in the reflectivity response indicates the high carbon incorporation and the good surface quality in spite of the CCl4 etching effect. The hole concentration tends to saturate at about 1.5×1020cm−3. The comparison between Hall effect measurements realized on sets of as grown and annealed layers, and theoretical calculations of the mobility lead to the determination of the compensation ratio of the samples.The lattice matching conditions were systematically investigated by using high X-ray diffraction measurements from (004) and (115) planes. A comparison between the experimental mismatch and the one calculated with the Vegard's law allows the estimation of the possible origin of the compensation. Secondary ion mass spectrometry, scanning electron microscopy and atomic force microscopy have been used as complementary tools to characterize the films.

Influence of lattice‐matching on structural properties of GaInNAs epitaxial films grown on GaAs

We studied the relationship between lattice-matching and crystalline quality of GaInNAs films grown on GaAs(001) substrates. The lattice mismatch between GaInNAs and GaAs was varied from –0.35% to 0.29%, and the coherent growth of GaInNAs for all of sample in this study was confirmed by (224) X-ray reciprocal space mapping. The full-width at half-maximum (FWHM) of (004) rocking curves showed minimum at the lattice-matched condition, and the FWHM did not depend on N composition. In Raman scattering measurements with the spectrum range of nitrogen-related local-vibrational mode (Ga-N like LO2 mode), a broad peak at 470 cm–1 was observed for all of GaInNAs samples. In addition to the peak at 470 cm–1, a clear shoulder peak at 490 cm–1 which has been understood as stress-relaxation mode was observed only at the lattice-matched sample. It was found that the lattice-matching has a significant effects not only on the crystal axis orientation but also local stress relaxation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth and Characterization of InGaNAs Quaternary Alloys for the Fabrication of Long Wavelength MSM Photodetectors on GaAs Substrates

ABSTRACTIn this paper, the optical and electrical properties of both as-grown and annealed thick InxGa1−xNyAs1−y layers grown by metal organic chemical vapour deposition (MOCVD) are presented. Through careful control of the trimetylyindium (TMIn), dimetylyhydrazine (DMHy), trimethylgallium (TMGa) and arsine (AsH3) precursors, lattice matching conditions were achieved for epitaxial layers containing up to 3% nitrogen (0≤y≤0.03) and 11% indium (0≤x≤0.11) with bandgap wavelengths to 1.3 μm. Nomarski optical microscopy and double crystal x-ray diffraction (XRD) measurements are used to investigate surface morphology, material quality and lattice-matched conditions. There is little or no 10K photoluminescence from the as-grown layers; alloy activation through rapid thermal annealing must be performed to obtain observable photoluminescence peaks. Annealing is also performed to reduce the resistivity of the as-grown layers. Once annealed, the undoped layers exhibited p-type carrier concentrations of 5.5×1017 cm−3 and mobilities of 50 cm2/Vs. The DC and frequency response performance characteristics of metal-semiconductor-metal (MSM) photodetectors fabricated on both as-grown and annealed InGaNAs layers are examined and compared to similar structures fabricated using GaAs and InGaAs/InP epitaxial materials.