InGaAs/InAlAs in-plane superlattices grown on slightly misoriented (110) InP substrates by molecular beam epitaxy

InGaAs/InAlAs in-plane superlattices (IPSLs) composed of InAs/GaAs and InAs/AlAs monolayer superlattices were grown using molecular beam epitaxy. The substrates were misoriented (110) InP tilting 3° toward the [00 ] direction. We grew half monolayers of AlAs and GaAs and single monolayers of InAs alternately, keeping regular arrays of single monolayer steps. The structures were evaluated by transmission electron microscopy (TEM). In a transmission electron diffraction pattern from the ( 10) cross-section, we observed two types of superstructure spot pairs double-positioned in the [001] direction, indicating the formation of the intended IPSL structures. In a cross-sectional TEM dark-field image, we observed the InGaAs/InAlAs superlattice structures formed almost in the [001] direction. The mean period of the superlattices was approximately 4 nm, which was comparable to the terrace width expected from the substrate tilt angle. However, IPSL structures were not completely formed, i.e., the lateral interfaces meandered along the growth direction, and partial disorderings were often observed. The photoluminescence spectrum from the IPSL had a peak corresponding to the InGaAs (2 nm thick)/InAlAs (2 nm thick) superlattice in addition to a peak corresponding to the In_0.5Al_0.25Ga_0.25As alloy.     

Anisotropy in InGaAs/GaAs heterostructures grown by low-pressure MOVPE and CBE

InGaAs/GaAs heterostructures grown on (001) substrates by low-pressure MOVPE exhibit a measurable anisotropy in their structural, optical and electrical properties. This anisotropy occurs in structures which have undergone partial or complete strain relaxation and it can be strongly reduced by using slightly misoriented substrates. A comparison with similar structures grown by CBE indicates that this anisotropy is less important. This study suggests that strain relaxation is achieved by a combination of several mechanisms whose relative importance depends on the orientation of the substrate and on growth temperature which varies with the growth technique.     

Transmission electron microscopic evaluation of InGaAs/InAlAs in-plane superlattices grown on slightly misoriented (110)InP substrates by molecular beam epitaxy

InGaAs/InAlAs in-plane superlattices (IPSLs) consisting of InAs/GaAs and InAs/AlAs monolayer superlattices grown on slightly misoriented (110)InP substrates by molecular beam epitaxy have been structurally evaluated by transmission electron microscopy. We used (110)InP 3° tilted toward the [00 ] direction. The ISPLs were fabricated by an alternative growth of half monolayers of AlAs and GaAs and one monolayer of InAs while maintaining regular arrays of one monolayer steps on the growth surface. In electron diffraction patterns from the ( 10) cross-section, two types of superstructure spots double-positioned in the 001 direction are observed, consistent with the existence of the IPSLs. Dark-field imaging from the superstructure spots reveal a periodic diffraction contrast with an average lateral periodicity of about 4 nm, i.e., one terrace width. However, meandering of the vertical interface and partial disordering in the IPSLs are often observed. From high resolution ( 10) cross-sectional TEM images, the presence of IPSLs was also confirmed with an atomic scale resolution, although their vertical interface are meandering. In electron diffraction patterns from the (110) plan-view, extra-spots similar to those observed in the ( 10) cross-section were seen. Dark-field images from the superstructure spots indicated that the IPSLs were formed almost exactly along the 110 direction, suggesting that the steps on the growth surface are very straight along the 110 direction.     

Structural and electrical properties of InAlAs/InGaAs/InAlAs HEMT heterostructures on InP substrates with InAs inserts in quantum well

A complex study of the influence of nanoscale InAs inserts with thicknesses from 1.7 to 3.0 nm introduced into In_0.53Ga_0.47As quantum wells (QWs) on the structural and electrical properties of In_0.52Al_0.48As/In^0.53Ga_0.47As/In_0.52Al_0.48As heterostructures with one-sided δ-Si-doping has been performed. The structural quality of a combined QW was investigated by transmission electron microscopy. A correlation between the electron mobility in QW with the thickness of InAs insert and the technology of its fabrication is established. Specific features of the InP(substrate)/InAlAs(buffer) interface are investigated by transmission electron microscopy and photoluminescence spectroscopy. A relationship between the energy positions of the peak in the photoluminescence spectra in the range of photon energies 1.24 eV < ?ω < 1.38 eV, which is due to the electronic transitions at the InP/InAlAs interface, and the structural features revealed in the interface region is established. It is found that an additional QW is unintentionally formed at the InP/InAlAs interface; the parameters of this QW depend on the heterostructure growth technology.     

Influence of semi-insulating InP substrates on InAlAs epilayers grown by molecular beam epitaxy

Tensile-strained InAlAs layers have been grown by solid-source molecular beam epitaxy on as-grown Fe-doped semi-insulating (SI) InP substrates and undoped SI InP substrates obtained by annealing undoped conductive InP wafers (wafer-annealed InP). The effect of the two substrates on InAlAs epilayers and InAlAs/InP type II heterostructures has been studied by using a variety of characterization techniques. Our calculation data proved that the out-diffusion of Fe atoms in InP substrate may not take place due to their low diffusion coefficient. Double-crystal X-ray diffraction measurements show that the lattice mismatch between the InAlAs layers and the two substrates is different, which is originated from their different Fe concentrations. Furthermore, photoluminescence results indicate that the type II heterostructure grown on the wafer-annealed InP substrate exhibits better optical and interface properties than that grown on the as-grown Fe-doped substrate. We have also given a physically coherent explanation on the basis of these investigations.     

Metamorphic InAs(Sb)/InGaAs/InAlAs nanoheterostructures grown on GaAs for efficient mid-IR emitters

High-efficiency semiconductor lasers and light-emitting diodes operating in the 3–5?μm mid-infrared (mid-IR) spectral range are currently of great demand for a wide variety of applications, in particular, gas sensing, noninvasive medical tests, IR spectroscopy etc. III-V compounds with a lattice constant of about 6.1?Å are traditionally used for this spectral range. The attractive idea to fabricate such emitters on GaAs substrates by using In(Ga,Al)As compounds is restricted by either the minimum operating wavelength of ～8?μm in case of pseudomorphic AlGaAs-based quantum cascade lasers or requires utilization of thick metamorphic In_xAl_1-xAs buffer layers (MBLs) playing a key role in reducing the density of threading dislocations (TDs) in an active region, which otherwise result in a strong decay of the quantum efficiency of such mid-IR emitters. In this review we present the results of careful investigations of employing the convex-graded In_xAl_1-xAs MBLs for fabrication by molecular beam epitaxy on GaAs (001) substrates of In(Ga,Al)As heterostructures with a combined type-II/type-I InSb/InAs/InGaAs quantum well (QW) for efficient mid-IR emitters (3–3.6?μm). The issues of strain relaxation, elastic stress balance, efficiency of radiative and non-radiative recombination at T?=?10–300?K are discussed in relation to molecular beam epitaxy (MBE) growth conditions and designs of the structures. A wide complex of techniques including in-situ reflection high-energy electron diffraction, atomic force microscopy (AFM), scanning and transmission electron microscopies, X-ray diffractometry, reciprocal space mapping, selective area electron diffraction, as well as photoluminescence (PL) and Fourier-transformed infrared spectroscopy was used to study in detail structural and optical properties of the metamorphic QW structures. Optimization of the growth conditions (the substrate temperature, the As₄/III ratio) and elastic strain profiles governed by variation of an inverse step in the In content profile between the MBL and the InAlAs virtual substrate results in decrease in the TD density (down to 3?×?10⁷ cm^?2), increase of the thickness of the low-TD-density near-surface MBL region to 250–300?nm, the extremely low surface roughness with the RMS value of 1.6–2.4?nm, measured by AFM, as well as rather high 3.5?μm-PL intensity at temperatures up to 300?K in such structures. The obtained results indicate that the metamorphic InSb/In(Ga,Al)As QW heterostructures of proper design, grown under the optimum MBE conditions, are very promising for fabricating the efficient mid-IR emitters on a GaAs platform.     

Raman and photoluminescence analyses of the crystalline InAlAs layer grown on InP substrate

Photoluminescence and Raman measurements are used to characterize the In_xAl_1-xAs (0.48 < × <0.573)epilayers grown on InP substrate by molecular beam epitaxy. It is found that as In composition, x, deviates too much from 0.52, misfit dislocations may be introduced. These dislocations will dramatically reduce the radiative efficiency of the InAlAs epilayers. Raman spectra become broader and more asymmetry due to alloy potential fluctuations as the mismatch becomes large.     

Molecular beam epitaxial growth and thermodynamic analysis of InGaAs and InAlAs lattice matched to InP

Reflection high-energy electron diffraction (RHEED) intensity oscillations have been used to detect the onset of metal droplet formation on the surface of InAs, InGaAs and InAlAs during molecular beam epitaxy. The growth conditions which produce such droplets are shown to be in good agreement with predictions based on thermodynamic arguments.     

Structural Characteristics of Epitaxial Low-Temperature Grown {InGaAs/InAlAs} Superlattices on InP(100) and InP(111)A Substrates

Crystallography Reports - The structural characteristics of {InGaAs/InAlAs} superlattices, grown by molecular-beam epitaxy (MBE) at a temperature of 200°C on InP substrates with the...     

Hydrogen removal by annealing from C-doped InGaAs grown on InP by metalorganic chemical vapor deposition

Hydrogen removal from C-doped InGaAs grown on InP substrate by metalorganic chemical vapor deposition is discussed based on the dependence of hole concentration on various annealing conditions. It is revealed that the hydrogen removal rate becomes higher as the annealing temperature is higher and the activation energy of hydrogen removal is about 1.9 eV regardless of C-doped layer thickness. The hydrogen removal rate is also found to be inversely proportional to C-doped layer thickness, suggesting that the hydrogen removal reaction is mainly governed by hydrogen diffusion.     

Crystal structure of stacking faults in InGaAs/InAlAs/InAs heterostructures

Stacking faults and dislocations in InGaAs/InAlAs/InAs heterostructures have been studied by electron microscopy. The use of different techniques of transmission electron microscopy (primarily, highresolution dark-field scanning transmission electron microscopy) has made it possible to determine the defect structure at the atomic level.     

Alloy phase separation in InAs/InAlAs/InP nanostructure superlattices studied by finite element calculation

The alloy phase separation effect in InAlAs spacer layer of InAs/InAlAs nanostructure superlattices was studied by two-dimensional finite element calculation. The calculation results showed that InAs islands with wide top would prefer to induce “V”-like In-rich InAlAs arms above InAs islands in InAlAs spacer layer, while InAs islands with narrow top would promote the formation of “I”-like In-rich InAlAs arms above InAs islands in InAlAs spacer layer which corresponded well with the experimental results reported in Ref. [9].     

In-situ photoluminescence and capacitance-voltage characterization of InAlAs/InGaAs regrown heterointerfaces by molecular beam epitaxy

This paper characterizes the electronic properties of InAlAs/InGaAs molecular beam epitaxy (MBE) regrown interfaces by combined use of in-situ photoluminescence surface state spectroscopy (PLS³) and capacitance-voltage (C-V) techniques. It is shown that the interface state density at the continuously grown InAlAs/InGaAs interface is low and comparable with that of the uninterrupted AlGaAs/GaAs interface, and that the effect of the growth interruption was surprisingly small, whereas the same interruption resulted in almost 10² times reduction of the PL efficiency for the AlGaAs/GaAs system. It is also shown that a high density of surface states exists at the MBE InGaAs surface. Interruption after the growth of the bottom InAlAs layer in the InAlAs/InGaAs/InAlAs system also leads to appreciable generation of interface states, but it is much smaller as compared with the case of the AlGaAs/GaAs/AlGaAs system.     

Low-temperature LPE Overgrowth of InGaAs/InP Mesa Heterostructure

Preparation of planar buried mesa ridge (PBMR) epitaxial wafers suitable for integrated optoelectronic circuits is presented. For this purpose the LPE growth of InP and InGaAsP (λ_g = 1.3 μm) below 600 °C on nonplanar ridge pattern was realized. Etching of the InGaAsP/InP ridge structure with ridge of 2–2.5 μm was found to be reproducible when HBr:H₂O₂:H₂O etchant was used. The best PBMR epitaxial wafers were obtained via regrowth in multiple-bin sliding boat by two thin layers of InP using a combination of one- and two-phase growth processes between 600 and 594 °C.     

Growth of InP/InGaAs multiple quantum well structures by chemical beam epitaxy

InP/InGaAs multiple quantum well structures with up to 200 periods have been grown by CBE. These structures exhibit exceptional lateral uniformity, measured as ±1 Å in period, ±13 ppm in lattice mismatch and ±0.5 nm in wavelength across a 2 inch wafer. Good surface morphology, sharp interfaces and excellent growth control have all been demonstrated.     

High-quality InP grown by chemical beam epitaxy

InP films were grown by chemical beam epitaxy using trimethylindium (TMI) and pure phosphine (PH₃) in a flow control mode with hydrogen as the carrier gas, with the TMI flow rate fixed at 3 SCCM. Substrate temperatures were varied between 505 and 580°C and V/III ratios from 3 to 9. InP layers with high optical quality (intense and narrow excitonic transition lines) and high crystalline quality (narrow and symmetric X-ray diffraction peaks) could be grown only within a narrow parameter window around a substrate temperature of 545°C (δT_s ≤ 25°C) and a V/III ratio of 5.5 (δ(V/III) ≤ 2). Carrier densities of 8 × 10¹⁴ cm^-3 with mobilities of 70000 cm²/V.s measured at 77 K were obtained for growth conditions close to the edge of this parameter window towards low V/III ratios. The growth rate of inP was also clearly at its maximum in the given parameter window. Leaving the window, by changing either the growth temperature or the V/III ratio, significantly decreased the growth rate. This reduced growth rate was accompanied by a degradation in the crystalline quality. We also demonstrate that for higher TMI flow the parameter window shifts to higher growth temperatures. The InP could be doped effectively with Si in the range from 9 × 10¹⁵ to 3 × 10¹⁸ cm^-3.     

CBE growth of InGaAsP/InP multiple quantum wells for optical modulator applications

The incorporation of group III and group V in the chemical beam epitaxy of InGaAsP/InP multiple quantum well structures has been studied in the temperature range of 470 to 550°C. Both Ga/In and P/As composition ratios are found to be strongly dependent on the growth temperature. The enhancement of phosphorus incorporation at high temperature is identified for the first time, which has a profound impact on the incorporation of group III, in particular the adsorption/pyrolysis of triethygallium. With accurate growth temperature control, high quality InGaAsP/InP superlattices with a large number of periods can be grown under continuous growth mode. Clear quantum confined Stark effect near 1.5 μm has been observed in a p-i-n test modulator structure.     

InGaAsP/InP multiple quantum wells grown by gas-source molecular beam epitaxy

We have grown In₁-_xGa_xAs_yP₁-_y/InP multiple quantum well structures with 1.3 μm excitonic absorption at room temperature by gas-source molecular beam epitaxy. In-situ composition determination in GaAs₁-_xP_x and InAs_xP₁-_x was carried out by measuring group-V-induced intensity oscillations of reflection high-energy electron diffraction. Based on the in-situ composition calibration for these ternary end members, Ga and As compositions in the quaternary compound, In₁-_xGa_xAs_yP₁-_y, were controlled successfully. Measurements by X-ray rocking curve, low-temperature photoluminescence and absorption spectroscopy indicate that high-quality In₁-_xGa_xAs_yP₁-_y/InP multiple quantum well samples were obtained.     

Highly uniform AlGaAs/GaAs and InGaAs(P)/InP structures grown in a multiwafer vertical rotating susceptor MOVPE reactor

Highly uniform AlGaAs/GaAs and InGaAs(P)/InP epitaxial layers have been grown in a vertical rotating susceptor MOVPE reactor capable of accommodating three 2′ wafers. The unique water-cooled “showerhead”-type injection distributor which is located 1.5 cm above the substrates ensures a uniform reactant distribution, resulting in uniform growth over a wide range of growth conditions. Periodic multilayer and single layer structures have been used to investigate the thickness and compositional uniformities. The thickness variations over a radial distance of 48 mm for three wafers grown in the same run are within ± 2% for both AlGaAs and InGaAs layers, resulting in a standard deviation of only 0.9%. The gallium concentration of an InGaAs layer varies from 46.88% to 47.01% over the same radial distance with the standard deviation of 0.043%. Measurements of InGaAsP layers grown onto 2′ InP wafers with different alloy compositions show good compositional uniformity yielding standard deviations within 4.4 nm in PL wavelength and 135 ppm in lattice mismatch over a 46 mm radial distance.     

Generation mechanism of CuAu-I type ordered structures in InGaAs crystals grown on (110) InP substrates by molecular beam epitaxy

The generation mechanism for CuAu-I type ordered structures in InGaAs grown on (110) InP substrates by molecular beam epitaxy is discussed. On the basis of previous work together with considerations of the atomic arrangement of the ordered structure and surface reconstruction on the (110) plane, we propose four possible models for the ordering. Through precise evaluation of these models, two models are selected as the most probable ones: these involve formation of the ordered structures on surfaces dominated by two monolayer steps. This model have been experimentally proven by the analyses of electron diffraction patterns from different crystals grown on different growth surfaces.