Microhardness of silicon layers grown by liquid phase epitaxy

The microhardness of silicon epilayers grown from Sn fluxes is found to be lower than that of the silicon substrates and to significantly depend on the crystallographic orientation of the substrates. The microhardness values follow a Gaussian distribution in all of the epilayers. Unintentional impurities are shown to have a significant effect on the microhardness of the epilayers. The addition of ytterbium to the high-temperature solution reduces the microhardness of the epilayers.     

Surface roughness studies on 4H-SiC layers grown by liquid phase epitaxy

The surface roughness on 4H-SiC layers grown by LPE was systematically studied. The surface morphology was investigated by scanning electron microscopy and atomic force microscopy. Depending on the substrate orientation two different types of growth morphology were found: terraced and step flow growth. The height of growth steps was found to depend on the angle of the substrate off-orientation. The higher the degree of substrate off-orientation the higher the step height. The terrace height depends on the impurity concentration in LPE layers. With the decrease of the impurity level, the terrace height has been significantly decreased.     

Diffusion of tin in lead tin telluride epitaxial layers grown by liquid phase epitaxy

The distribution of tin in epitaxial layers of lead tin telluride grown by liquid phase epitaxy on lead telluride substrates has been determined by electron probe microanalysis. The diffusion coefficients calculated from the experimental data agree approximately with the literature values.     

An optical investigation of transient layers in magnetic garnet films grown by liquid phase epitaxy

The growth of garnet films using Liquid Phase Epitaxy has led not only to materials with improved performance for bubble domain memories but to materials which exhibit improved microwave properties as well. We have investigated the optical properties of such films and found that there exist transient layers at the substrate/film interface and at the film/air interface. Our results and conclusions regarding the substrate/film interface do not agree with those of Davies et al⁽¹⁾. The discovery of a post growth lead rich layer has not been previously reported to our knowledge and has important implications for both bubble domain and optical applications of garnet films.     

P-type InP grown by liquid phase epitaxy with rare earths: not intentional Ge acceptor doping

InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP:Fe substrates with praseodymium added to the melt. Room temperature Hall effect measurements revealed p-type conductivity of the layers with the hole concentration 6×10¹⁴ cm⁻³ and mobility 150 cm² V⁻¹ s⁻¹. By measuring temperature dependence of the hole concentration the binding energy of the dominant acceptor was determined as 223 meV. A photoluminescence line was found at 1.195 eV, close to the previously estimated no-phonon line of Ge acceptor transitions in Ge doped n-type InP. It was concluded that Ge acceptors cause the p-type conductivity of the grown layers.     

Spectroscopic evaluation of the structural and compositional properties of GaNxAs1−x superlattices grown by molecular beam epitaxy

GaN_xAs_1−x multiple-quantum-well (MQW) samples (x ≤ 0.025) grown by molecular beam epitaxy have been studied by photoluminescence (PL) spectroscopy, high-resolution X-ray diffraction (HR-XRD), secondary-ion mass spectrometry (SIMS) and ultra-high-resolution infrared local-vibrational-mode (IR LVM) spectroscopy in order to determine their compositional and structural properties. Compositional data from PL spectroscopy and HR-XRD, derived using simple models of the superlattice structure, show good agreement. SIMS depth profiles show that the wells are triangular, and are wider and shallower than predicted, with nitrogen present in the barrier layers. A comparison between SIMS and HR-XRD suggests the presence of interstitial nitrogen for samples with the highest nominal concentrations. By contrast, IR LVM measurements demonstrate that substitutional nitrogen incorporates linearly with increasing nitrogen fraction.     

Doping gradients in layers of gallium phosphide grown by liquid epitaxy

Layers of epitaxial gallium phosphide doped with either tellurium, sulphur or zinc over the range 10¹⁶ to 10¹⁸ cm⁻³ have been grown from gallium solution using a vertical dipping system. These layers of thickness 60 to 80 μm have been produced on the (100) and (111)B faces of gallium phosphide single crystal substrates at high growth rates. Doping gradients have been investigated by a Schottky barrier technique over an angle lapped region of the grown slice, measuring the capacitance voltage characteristics of the individual barriers. Significant changes in doping level have been observed throughout the thickness of the layers and these are related to the variation of distribution coefficient, the losses of impurity from the system and the presence of competing background impurity systems.     

Photoreflectance study of strained GaAsN/GaAs T-junction quantum wires grown by metal-organic vapor phase epitaxy

Strained GaAsN T-junction quantum wires (T-QWRs) with different N contents grown on GaAs by two steps metal-organic vapor phase epitaxy in [001] and [110] directions, namely QW1 and QW2 respectively, have been investigated by photoreflectance (PR) spectroscopy. Two GaAsN T-QWRs with different N contents were formed by T-intersection of (i) a 6.4-nm-thick GaAs0.89N0.011 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2 and (ii) a 5.0-nm-thick GaAs0.985N0.015 QW1 and a 5.2-nm-thick GaAs0.968N0.032 QW2. An evidence of a one-dimensional structure at T-intersection of the two QWs on the (001) and (110) surfaces was established by PR resonances associated with extended states in all the QW and T-QWR samples. It is found that larger lateral confinement energy than 100 meV in both of [001] and [110] directions were achieved for GaAsN T-QWRs. With increasing temperature, the transition energy of GaAsN T-QWRs decreases with a faster shrinking rate compared to that of bulk GaAs. Optical quality of GaAsN T-QWRs is found to be affected by the N-induced band edge fluctuation, which is the unique characteristic of dilute III-V-nitrides.     

Effect of substrate conductivity on the thickness and composition of GaAlSb epitaxial layers grown by liquid phase epitaxy

It is shown experimentally that the thickness and composition of Ga_1 − xAl_xSb layers grown by liquid phase epitaxy on Gasb substrates depend on the conductivity type of the substrates. To avoid experimental uncertainties that naturally happen from an experiment to another one, such as changes in the exact liquid composition, growth temperature, temperature gradients, etc., the Ga_1 − xAl_xSb layers have been grown simultaneously from the same liquid solution on N and P type GaSb substrates. The X-ray rocking curves show that for every couple of layers, grown on N and P type substrates, there is a consistent difference between their thickness and composition. The thickness difference has also been verified by optical microscopy. A likely explanation of this effect is a change in surface energy of the substrate induced by the surface electric field normally present in semiconductors.     

Properties of Eu-Yb-Y magnetic garnet films grown by liquid phase epitaxy

Epitaxial films of Eu_yYb_zY_3?y?zFe_5?xGa_xO₁₂ have been deposited from PbO-B₂O₃ solution on (111) Gd₃Ga₅O₁₂ substrates. Saturation magnetization, characteristic length, coercivity, anisotropy and domain wall mobility are discussed in relation to film composition. The films exhibit reasonable mobilities, satisfactory quality factors and good temperature stability. The system appears to be a promising candidate for bubble device application.     

Ordered domain structures of nitrogen-doped GaInP layers grown by organometallic vapor phase epitaxy

Transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies have been performed on organometallic vapor phase epitaxial GaInP heterostructures grown on (001) GaAs singular and vicinal substrates to investigate nitrogen doping effect on the ordering and domain structures. TEM results show that well-defined order–disorder–order heterostructures are formed when nitrogen doping level is high. This indicates that nitrogen hinders the occurrence of ordering. For the singular samples, ordered domain structures are found to be dependent on the nitrogen doping level of the underlying layer, on which they are grown. The doping dependence of ordered structures and the formation of anti-phase boundaries are described based on surface undulations (i.e., hillocks) and step configuration.     

The transient layer in magnetic garnet films grown by liquid phase epitaxy

A thin (～ 0.1 μm) layer is formed initially during the so-called “transient” period preceding the establishment of the steady state diffusion boundary layer in the melt, when films are dipped in a horizontal plane while undergoing axial rotation. Further evidence is given for the existence of the transient as a separate and distinct growth mode as compared to steady state growth. The transient layer, which grows comparatively rapidly, nevertheless has properties virtually identical to those of the subsequently grown steady state layer, except for its higher Pb concentration.     

Transport property of Sn-doped In0.5Ga0.5P layers grown by liquid phase epitaxy

The temperature-dependent Hall mobility and carrier concentration of Sn-doped In_0.5Ga_0.5P epilayers grown on (100) semi-insulating GaAs substrates by the liquid phase epitaxy technique have been investigated in the range of 77–300 K. It was found that the Sn-doped In_0.5Ga_0.5P epilayer was heavily compensated with the compensation ratio of 0.4–0.6. It was also found that the Sn shallow donor has an ionization energy 17–12 meV with increasing carrier concentrations through Hall measurements. The model taking into account ionized impurity, alloy and space-charge scattering mechanisms is considered in order to properly portray the observed features of the electron mobility results. The theoretical prediction is in good agreement with the observed results. The electron mobility was limited by ionized scattering up to 120 K and was also limited by alloy, space-charge scattering up to 300 K.     

Yb:CaF2 grown by liquid phase epitaxy

Ytterbium doped CaF₂ crystalline layers have been grown for the first time from high temperature solutions at controlled atmosphere by using the liquid phase epitaxy technique. Doped layers having thicknesses between a few microns to a hundred of microns have been grown onto non-oriented and (1 1 1) oriented CaF₂ substrates. The Yb³⁺:CaF₂ layers show structural properties very close to the undoped substrate without any further thermal treatment. Registration of room temperature emission spectra and fluorescence lifetime measurements performed with epitaxial layers corresponding to different ytterbium concentrations show similar spectroscopic properties as in the bulk crystals.     

The structure of GaN layers grown on SiC and sapphire by molecular beam epitaxy

A comparative study of the defects at the interfaces and inside the layers was carried out in GaN/AlN epitaxial layers on SiC and sapphire. Whereas surface cleaning of the sapphire substrates is rather standardised now, the SiC substrates cleaning is still to optimise conditions, as the high densities of defects inside the epitaxial layers cannot be explained solely by the 3.54% lattice mismatch. The investigated specimens were grown by molecular beam epitaxy (MBE), either assisted by electron cyclotron resonance or an NH₃ gas source system to provide atomic nitrogen. Assuming that MBE is a growth technique more or less close to equilibrium, the observed defects are interpreted and a growth mechanism, for GaN layers on the stepped (0001) SiC and sapphire surfaces, is proposed.     

Luminescence properties of hole traps in homojunction gallium nitride diodes grown by metal organic vapour phase epitaxy

A detailed investigation on p–n junction diodes of GaN using deep level transient Fourier spectroscopy (DLTFS) has been carried out. The typical deep level spectra on the various diodes on the same wafer demonstrate three electron levels labelled as E1, E2 and E3 and a hole trap H1 together with a broad band constituting three new hole levels H2, H3 and H4 therein. The electrical parameters like activation energy, trap concentration and capture cross section due to the observed levels have been measured for the comparison with the literature. The hole levels H1–H4 are found to be potentially involved in the radiative recombination and thereby, the luminescence role of the levels in the device is discussed.     

HgCdTe/CdZnTe液相外延材料的倒易空间图研究

采用高分辨X射线衍射的例易空间图研究了HgCdTe／CdZnTe(-0．044％晶格失配)液相外延材料界面处品格结构，结果显示，通常使用的10μm厚的碲镉汞液相外延材料的晶格相对碲锌镉衬底已处于完全弛豫状态，并且外延层和衬底的品向发生了0．01。的偏离，但是，由于外延层中存在着组分梯度以及衬底和外延层热膨胀系数存在着差异，界面处外延层中仍存在着应力和应变。对称衍射和非对称衍射的实验结果均显示外延材料的例易空间图沿垂直于散射矢量方向有所扩展．这一结果表明晶格失配的弛豫使得界面处外延层的晶体结构呈镶嵌结构。实验也发现，外延层的非对称衍射倒易空间图的扩展偏离散射矢量方向，根据弛豫线模型，这也是由于界面处外延层存在组分梯度和应变梯度所造成的。     

Microstructure characterization of InAs0.93Sb0.07 films grown by ramp-cooled liquid phase epitaxy

InAs_0.93Sb_0.07 alloy thin films were grown by ramp-cooled liquid phase epitaxy on (100) InAs substrate using horizontally sliding multi-wells graphite boats. The systematic microstructural characterizations of the epi-grown films were analyzed by X-ray diffraction, scanning electronic microscopy and energy dispersive spectra. Four typical surface morphologies of the films were observed, which depend sensitively on growth parameters such as the growth temperature, the substrate etching time, the flux of the hydrogen, and the cooling range and rate. The film shows high crystal perfection with (100) orientation, as evidenced by X-ray measurement. The crystal quality of the epilayer was evaluated by the X-ray double axes diffraction, and the dislocation density was estimated through fitting the (200) and (400) rocking curves by Gaussian lineshape.