Structure characterization of MHEMT heterostructure elements with In<Subscript>0.4</Subscript>Ga<Subscript>0.6</Subscript>As quantum well grown by molecular beam epitaxy on GaAs substrate using reciprocal space mapping

The crystallographic parameters of elements of a metamorphic high-electron-mobility transistor (MHEMT) heterostructure with In_0.4Ga_0.6As quantum well are determined using reciprocal space mapping. The heterostructure has been grown by molecular-beam epitaxy (MBE) on the vicinal surface of a GaAs substrate with a deviation angle of 2° from the (001) plane. The structure consists of a metamorphic step-graded buffer (composed of six layers, including an inverse step), a high-temperature buffer of constant composition, and active high-electron-mobility transistor (HEMT) layers. The InAs content in the metamorphic buffer layers varies from 0.1 to 0.48. Reciprocal space mapping has been performed for the 004 and 224 reflections (the latter in glancing exit geometry). Based on map processing, the lateral and vertical lattice parameters of In_xGa_1–xAs ternary solid solutions of variable composition have been determined. The degree of layer lattice relaxation and the compressive stress are found within the linear elasticity theory. The high-temperature buffer layer of constant composition (on which active MHEMT layers are directly formed) is shown to have the highest (close to 100%) degree of relaxation in comparison with all other heterostructure layers and a minimum compressive stress.     

Relaxation and recovery processes of AlxGa1−xN grown on AlN underlying layer

The processes as in title of relaxation of the lattice mismatch and the recovery of crystalline quality in thick Al_xGa_1−xN on high-temperature-grown AlN were investigated. When x=0.3, rapid lattice relaxation occurred over a few microns, then the crystalline quality gradually recovered over 10 μm. In contrast, when x=0.7, relaxation of the lattice mismatch gradually occurred over 5 μm.     

X-ray diagnostics of P-HEMT AlGaAs/InGaAs/GaAs structures

The structural characteristics of the P-HEMT AlGaAs/InGaAs/GaAs heterostructure have been studied by high-resolution X-ray diffractometry. The parameters of the heterostructure layers were determined by simultaneous analysis of the X-ray reflection curves for the (004) and (113) crystallographic planes. Interface diffusion has been established for the In_yGa_1?yAs quantum well and the Al_xGa_1?x As spacer layer, which are characterized by reconstructed profiles of the lattice parameter distribution and anisotropic distribution of random displacements in the layer plane and in the perpendicular direction.     

X-ray investigation on GaAlAs/GaAs epilayers bending at temperatures 77–750 K

The Bond method of precise lattice constants measurements and double crystal (+, −) (004) reflections were applied to measure lattice constants, lattice mismatch, thickness of the layers and samples bending in temperature 77–750 K. The results enabled to calculate the ratio of GaAs and Ga_1−xAl_xAs elastic constants as well as thermal expansion coefficients.     

MOVPE Growth of Wide Band-Gap II—VI Compounds for Near-UV and Deep-Blue Light Emitting Devices

We report on the growth by metalorganic vapour phase epitaxy of high structural and optical quality ZnS, ZnSe and ZnS/ZnSe multiple quantum well (MQW) based heterostructures for applications to laser diodes operating in the 400 nm spectral region. High purity ^tBuSH, ^tBu₂Se and the adduct Me₂Zn:Et₃N were used as precursors of S, Se and Zn, respectively. The effect of the different MOVPE growth parameters on the growth rates and structural properties of the epilayers is reported, showing that the crystallinity of both ZnS and ZnSe is limited by the kinetics of the incorporation of Zn, S and Se species at the growing surface. Very good structural and optical quality ZnS and ZnSe epilayers are obtained under optimized growth conditions, for which also dominant (excitonic) band-edge emissions are reported. The excellent ZnS and ZnSe obtained by our MOVPE growth matches the stringent requirements needed to achieve high quality ZnS/ZnSe MQWs. Their structural properties under optimized MOVPE conditions are shown to be limited mostly by the formation of microtwins, a result of the intrinsic high lattice mismatch involved into the ZnS/ZnSe heterostructure. Despite the large amount of defects found, the optical quality of the MQWs turned out to be high, which made possible the full characterization of their electronic and lasing properties. In particular, photopumped lasing emission up to 50 K in the 3.0 eV energy region are reported for the present MQWs heterostructures under power excitation density above 100 kW/cm².     

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.     

TEM analysis of the container effect of Au‐based catalyst droplets during vapour‐liquid‐solid growth of axial ZnTe/CdTe nanowires

Axial heterostructure nanowires (NWs) of ZnTe/CdTe were grown by vapour‐liquid‐solid growth realized in a molecular beam epitaxial chamber. By alternative supply of Zn or Cd and constant Te the heterostructure was generated. The liquid phase is provided by a Au‐based eutectic droplet which stays at the tip of the NW during the entire growth. For structural and chemical characterization by TEM the NWs were harvested from the substrate and transferred to a holey carbon film. The NWs exhibit an expansion of the diameter correlated with the interface region between ZnTe and CdTe. Idiomorphic growth of the CdTe is evident from electron diffraction experiments. The growth rate of CdTe appears to be smaller compared to that of ZnTe at the same temperature. Both, quantitative high‐resolution TEM and energy dispersive X‐ray spectroscopy line scans reveal a smeared ZnTe/CdTe interface along about 200 nm. The smearing is due to both, the liquid catalyst which buffers the supply of Cd instead of Zn at the liquid/solid interface and to the strain which is induced by the lattice mismatch. It forces the system to consume the remnant Zn for the NW growth in favour of Cd. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermodynamic analysis of vapor-phase epitaxial growth of GaAsN on Ge

In this paper, we use thermodynamic analysis to determine how the nitrogen (N) ratio in the source gases affects the solid composition of coherently grown GaAs_1?xN_x(x～0.03). The source gases for Ga, As, and N are trimethylgallium ((CH₃)₃Ga), arsine (AsH₃), and ammonia (NH₃), respectively. The growth occurs on a Ge substrate, and the analysis includes the stress from the substrate–crystal lattice mismatch. Calculation results indicate that to have just a few percent N incorporation into the grown solid, the V/III ratio in the source gases should be several thousands and the input-gas partial-pressure ratio NH₃/(NH₃+AsH₃) should exceed 0.99. We also find that the lattice mismatch stress from the Ge substrate increases the V/III source–gas ratio required for stable growth, whereas an increase in input Ga partial pressure ratio has the opposite effect.     

Controlled lattice constant mismatch by compositional changes in liquid phase epitaxially grown single crystal films of rare earth yttrium iron gallium garnets on gadolinium gallium garnet substrates

Liquid phase epitaxy (LPE) by dipping substrates into supercooled fluxed solution provides a convenient way of changing the melt and film composition. The apparatus, method and composition of the melts that we use will be described in detail. The composition of the layer is essentially Y₃GaFe₄O₁₂, which has a smaller lattice constant than the Czochralski-grown gadolinium gallium garnet substrate. By substitutions such as gadolinium, samarium or lanthanum for yttrium the lattice constant mismatch can be controlled. The effect of these substitutions on film properties such as cracks, stresses and magnetic domain pattern as well as the interaction of substrate defects such as dislocations with the epitaxially-grown film are discussed.     

Thermal Expansion of SrF2 at Elevated Temperatures

The X-ray method was used to determine the linear thermal expansion coefficient of SrF₂ in the temperature range from 301 to 1173 K. A comparison of the thermal expansion coefficients of CaF₂, SrF₂ and BaF₂ at T > 300 K shows that the degree of lattice an–harmonicity in the alkaline earth fluorides decreases with increasing mass of the alkaline earth atom. The results for the thermal expansion of SrF₂ are used to discuss the temperature dependence of the lattice mismatch in the SrF₂/InP film–substrate system.     

Optical anisotropy associated with growth striation of yttrium garnet,Y3 (Al,Fe)5O12

The optical anisotropy associated with growth striae of yttrium garnet, Y₃(Al, Fe)₅O₁₂, was studied in terms of optical microscopy and EPMA analysis. It turned out that the lattice mismatch due to the compositional change at the growth striae gives rise to stressbirefringence. The result can be applied to compositional characterization of garnet single crystal by determining the vibration directions of polarized rays under a microscope.     

GaP?AlxGa1−xP heterostructure edge coupling waveguides for hybrid integrated optic devices

In this paper we present the performance of GaP Al_xGa_1−xP heterostructure waveguides for integrated optic hybrid devices. The waveguide layer is graded with a parabolic refractive index profile for the light emission of a DH GaAs semiconductor laser. The waveguide heterostructure performed allows to couple at it edge crossection semiconductor laser or photodetector as well as fix or solder them on the same substrate on which the heterostructure layers were deposited. The heterostructure layers were grown by liquid phase epitaxy and the heterostructure waveguide was performed by means of etching technics specially developed for this purpose. Both, the growth procedure, as well as the etching technics are described. The results achieved are shown in curves and photographs, taken on a scanning microscope.     

Metamorphic growth of tensile strained GaInP on GaAs substrate

Optical and structural properties of tensile strained graded Ga_xIn_1−xP buffers grown on GaAs substrate have been studied by photoluminescence, X-ray diffraction, atomic force microscopy, and scanning electron microscopy measurements. The Ga composition in the graded buffer layers was varied from x=0.51 (lattice matched to GaAs) to x=0.66 (1% lattice mismatch to GaAs). The optimal growth temperature for the graded buffer layer was found to be about 80–100 °C lower than that for the lattice matched GaInP growth. The photoluminescence intensity and surface smoothness of the Ga_0.66In_0.34P layer grown on top of the graded buffer were strongly enhanced by temperature optimization. The relaxation of tensile GaInP was found to be highly anisotropic. A 1.5 μm thick graded buffer led to a 92% average relaxation and a room temperature photoluminescence peak wavelength of 596 nm.     

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)_relax ～ (1.1–1.2) × 10^–4 is recorded in isotopically modified ¹³С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.     

Composition latching phenomenon and lattice mismatch effects in LPE-grown In1−xGaxAs on InP substrate

We describe the possible composition range of In_1?xGa_xAs grown directly on InP substrates by LPE, the expansion of the range by use of In_0.53Ga_0.47As as a buffer layer, and the composition latching phenomenon in which only an x = 0.445 ± 0.005 layer is grown from the melt of any solidus composition between 0.40 and 0.45. This phenomenon does not occur on the larger composition side relative to the lattice matching compostition of x = 0.47, but only on the smaller side. The effects of the growth temperature, cooling rate, and step-cooling interval on this phenomenon, and the effects of the lattice mismatch on the crystal perfection and surface morphology are also described.     

Thick LPE Layers of InAs1—xSbx for 3—5 μm Optoelectronic Applications

N-InAs_1—xSb_x/n, p-InAs heterostructures were grown by liquid phase epitaxy on (100) oriented substrates. The layer composition was varied in the interval 0 < x < 0.1, the corresponding lattice mismatch being not greater than 0.5%. The layer composition was studied by microprobe analysis on the surface of the structure cross-section. Microhardness profiles were investigated using Vickers and Knoop indentors. Raman scattering was also studied.     

A method of investigation of heterostructure for junction lasers based on photoluminescence measurements

A four layer GaAs–Al_xGa_1–xAs heterostructure photoluminescence spectrum measured at 77K has been compared with the results of investigations concerning the composition of this heterostructure, performed by using the electron microprobe JXA-50A. The application of photoluminescence investigations of such heterostructures as a simple and convenient control method that can be used during the performance of a heterostructure laser has been proposed.     

Influence of the graduated composition region on the properties of GaInAs epitaxial layers grown on GaAs substrates

The electrical properties of Ga_1-xIn_xAs layers (0 < x < 0.3) are investigated. The layers are grown on <111> oriented GaAs substrates. A transition layer is grown with an increasing indium content to decrease the mismatch of the lattice parameters of the substrate and the final layer. A special many-section crucible is used. In dependence on composition the decrease both of mobility and carrier concentration with the increase of compensation is observed. These facts are connected with the introducing of additional acceptors without donor concentration changes.     

Effect of the sign of misfit strain on the formation of a dislocation structure in SiGe epitaxial layers grown on Si and Ge substrates

Comparative analysis of the specific features of the formation of a dislocation structure in the single-layer epitaxial heterostructures Si_1?xGe_x/Si and Ge_1?ySi_y/Ge is performed. It is ascertained that, at a relatively low lattice mismatch between an epitaxial layer and a substrate, the sign of misfit strain at the interface significantly affects the processes of defect formation. The most probable reasons for the observed phenomena are analyzed with allowance for the specific features of the state of the ensemble of intrinsic point defects in epitaxial layers subjected to elastic strains of a different sign.     

Method for measurement of lattice parameter of cubic GaN layers on GaAs (0 0 1)

An extended technique derived from triple-axis diffraction setup was proposed to measure lattice parameters of cubic GaN(c-GaN) films. The fully relaxed lattice parameters of c-GaN are determined to be 4.5036±0.0004 Å, which is closer to the values of a hypothetical perfect crystal. The speculated zero setting correction (Δθ) is very slight and within the range of the accuracy of measurement. Additionally, we applied this method to analyze strain of four different kinds of c-GaN samples. It is found that in-plane strain caused by large lattice mismatch and thermal expansion coefficients mismatch directly influence the epilayer growth at high temperatures, indicating that the relaxation of tensile strain after thermal annealing helps to improve the crystalline quality of c-GaN films and optical properties.