Molecular beam epitaxy of GaSb/AlxGa1 − xSb quantum well structures

Molecular beam epitaxy (MBE) is used to grow GaSb/Al_xGa_{1 − x}Sb quantum well (QW) structures on GaSb(001) substrates using both Sb₂ and Sb₄ molecules. While the optoelectronic properties of thick GaSb epitaxial layers are significantly affected by the type of molecule used, no influence is noted on the QW photoluminescence properties. It is shown that MBE allows a very precise and reproducible control of the QW structure parameters such as QW widths for which monolayer precision is obtained. Through the variation of the QW associated PL energy as a function of the growth temperature, the occurrence of a surface segregation-like phenomenon is evidenced. However, this effect is rather weak so that a good estimation of the valence band offset through the PL energy variation with the QW width can be made. Moreover, the QW width for which the Γ-L crossover occurs is very precisely determined.     

Laser-induced structural transformation of AsxSe1-x thin amorphous films

The changes in the optical and holographic recording properties of amorphous As_xSe_1-x films with 0 ≤ x ≤ 0.2 under laser irradiation have been measured. The dependence of the transmissivity and diffraction efficiency on the irradiation energy density shows two qualitatively different regions. Below an energy density threshold, E_th, only small changes in the local structure of the system can be detected. In this low-E region, the transmissivity varies reversibly with exposure. Qualitative explanation of the observed behavior may be based on associating such with alteration of deep defect states. Above E_th, the changes were attributed to crystallization transformation. The Raman spectra reveal the progressive transformation of the system from amorphous into the crystalline phase under laser irradiation.     

Structural and optical properties of quaternary AlInGaN epilayers grown by MOCVD with various TMGa flows

AlInGaN quaternary epilayers have been grown with various TMGa flows by metalorganic chemical vapor deposition to investigate the influence of growth rate on the structural and optical properties. Triple-axis X-ray diffraction measurements show AlInGaN epilayers have good crystalline quality. Photoluminescence (PL) measurements show that the emission intensity of AlInGaN epilayers is twenty times stronger than that of AlGaN epilayer with comparable Al content. V-shaped pits are observed at the surface of AlInGaN epilayers by atomic force microscopy (AFM) and transmission electron microscopy (TEM). High growth rate leads to increased density and size of V-shaped pits, but crystalline quality is not degraded.     

Effect of Asi on the optical properties of Ga1−xInxAs/InP grown by molecular beam epitaxy

This report focuses on the effect of the As species and the V/III ratio on the optical properties of Ga_1−xIn_xAs/InP grown by molecular beam epitaxy (MBE). The band gap energies of the layers were measured by low temperature photoluminescence (PL) while the indium contents x were determined by X-ray for samples in the investigated range of 0.50<x<0.56. For the analysis of these data we considered the model of Kuo et al. which we confined with a correction for the different measurement temperatures in PL (4.2 K) and X-ray (300 K). Using As₄ with an effective V/III ratio higher than 1.3, we find the best agreement of the band gap energies and predictions of the theory. A lower V/III ratio always implies a reduction of the band gap energy to values 5-15 meV lower than expected. In contrast, using As₂ the PL data fit quite well independent of the effective V/III ratio above unity.     

Photocurrent measurements on GaAs1−xNx epilayers grown by metalorganic chemical vapor deposition

GaAs_1−xN_x epilayers were grown on a GaAs(0 0 1) substrate by metalorganic chemical vapor deposition. Composition was determined by high resolution X-ray diffraction. Band gap was measured from 77 to 400 K by using photocurrent measurements. The photocurrent spectra show clear near-band-edge peak and their peak energies drastically decrease with increasing nitrogen composition due to band gap bowing in the GaAs_1−xN_x epilayers. Those red shifts were particularly notable for low nitrogen compositions. However, the shifts tended to saturate when the nitrogen composition become higher than 0.98%. When the nitrogen composition is in the range 1.68–3.11%, the measured temperature dependence of the energy band gap was nicely fitted. However, the properties for the nitrogen composition range 0.31–0.98% could not be fitted with a single fitting model. This result indicates that the bowing parameter reaches 25.39 eV for low nitrogen incorporation (x=0.31%), and decreases with increasing nitrogen composition.     

A new substrate holder for liquid-phase epitaxy by the dipping method and its application to Hg1-xCdxTe

This paper describes a substrate holder for liquid-phase epitaxy (LPE) by the dipping method and its use on Hg_1-xCd_xTe LPE. The holder consists of a shaft, a pivotable plate, and a paddle that is fed through the shaft. This holder automatically places the substrate in a horizontal position during dipping and in a vertical position during withdrawal ensuring uniform film growth and good melt drainage. The holder has been successfully used on the liquid-phase epitaxy of Hg_1-xCd_xTe and excellent results were obtained.     

The growth and characterization of ZnSe epilayers grown by VPE and MOCVD

Zinc selenide (ZnSe) is a useful semiconductor for homojunction or heterojunction optoelectronic devices. In this paper we review the fabrication techniques of vapor phase epitaxy (VPE) and metalorganic chemical vapor deposition (MOCVD) for the growth of ZnSe epilayers. These techniques can play important roles in achieving ZnSe blue light-emitting devices. Recent and future trends in growing these devices are also reviewed and studied.     

A study of growth and morphological features of TiOxNy thin films prepared by MOCVD

The growth and morphological features of MOCVD TiO_xN_y films have been characterized to evaluate the effect of various process parameters on film growth. XRD analysis of the films deposited at 600°C on Si(1 1 1) and mica show a TiN(1 1 1) peak at 2θ=36.6°, but only anatase peaks are detected below 550°C. Above 650°C, both anatase and rutile peaks are detected. The presence of ammonia is not effective below 550°C as the deposited film is mostly TiO₂. Also, ammonia does not play any role in homogeneous nucleation in the gas phase, as evident by the deposition of anatase/rutile particles above 650°C. The following changes in the morphological features are observed by varying process parameters. By increasing the ratio of titanium-isopropoxide to ammonia flow, the cluster shape changes from angular to rounded; dilution of the flow results in larger elongated clusters; increase in flow rate at constant precursor to ammonia ratios, changes the cluster shape from rounded to elongated and the cluster size deceases. Deposition at higher temperatures results in finer clusters with a slower growth rate and eventually results in a very thin film with particle deposition at 650°C and above.     

High carbon doping of Ga1−xInxAs (x≈0.01) grown by molecular beam epitaxy

We have grown layers of Ga_1−xIn_xAs:C (x ≈ 0.01) on (100) GaAs by molecular beam epitaxy. As C source a graphite filament was used. Structures coherent with the substrate were obtained by adjusting properly the In and C concentrations. With simultaneous incorporation of In and C the strain is compensated and, consequently, the defect density is reduced. A maximum hole concentration value of p = 6×10¹⁹ cm⁻³ was achieved, which is twice higher than the saturation value of C doping of GaAs produced under the same conditions. There is evidence that this value is not in the saturation limit. The product of the hole density times the mobility increases, so the resistance decreases with higher C doping. Raman spectra show that the C_As peak broadens and shifts to lower frequencies for increasing concentration of indium. In H-passivated samples, Raman spectroscopy shows that C_As is surrounded by Ga atoms only. Indium atoms are thus present only in the second group III shell.     

Crystal growth of MnxCd1-xGa2Se4 (0.00 x 0.20)

Crystals of Mn_xC_1-xGa₂Se₄ (0.00 x 0.20) have been grown the vapour phase by chemical transport modified by the t ime variation of the temperature profile procedure. Crystals with dimensions up to 15 × 2 × 2 mm were obtained and characterized by EPR spectroscopy.     

GaSb/GaAs异质结热光伏电池材料的MBE生长

利用分子束外延方法(MBE)在GaAs (001)衬底上外延生长了GaSb薄膜,并对GaSb薄膜进行了高温退火研究,利用高分辨透射电子显微镜(HRTEM)、原子力显微镜(AFM)、Hall效应(Hall Effect)和低温光荧光谱(LTPL)等手段对薄膜的晶体质量、电学性质和光学性质进行了研究.发现直接生长的GaSb膜表面平整,空穴迁移率较高.研究发现30 s、650℃的快速热退火可消除位错等缺陷,显著提高GaSb薄膜的光学质量.     

Calculation of the Refractive Indices of M1-xRxF2+x Crystals (M = Ca, Sr, Ba, Cd, Pb; R are Rare Earth Elements)

It is shown that the refractive indices of two-component M _1-x R _x F_2+x crystals (M = Ca, Sr, Ba, Cd, Pb; R = La-Lu, Y; 0 ≤ x ≤ 0.5) can be calculated with a rather high accuracy in a wide spectral range (depending on the rare-earth-element content) using molecular refraction additivity for the components.     

Growth of GaN/AlN and AlGaN by MOCVD using triethylgallium and tritertiarybutylaluminium

Films of aluminium nitride (AIN) with thicknesses in the range from 200 to 3600 Å have been deposited at 1050°C by low-pressure MOCVD. Using an alternative precursor, tritertiarybutylaluminium (^tBu₃Al), and ammonia (NH₃), we have grown AlN on sapphire (c-Al₂O₃). At a growth rate of 0.35 μm/h, the FWHM of the rocking curve measured by X-ray diffraction was 150 arcsec. Therefore, we used the thin AlN films as buffer layers for the deposition of gallium nitride (GaN) at 950°C using triethylgallium (Et₃Ga). Aluminium gallium nitride (Al_xGa_1−xN) with aluminium contents x from 0 to 0.5 were grown using a mixture of Et₃Ga and ^tBu₃Al. The strctural and optical properties of GaN, AlGaN and AlN were verified by X-ray diffraction (XRD), spectrally resolved photoconductivity (SPC), photothermal deflection (PDS) and photoluminescence spectroscopies.     

Electrical resistivity of amorphous Fe90-xCoxZr10 alloys: Weak localization and spin fluctuation effects

The results of electrical resistivity () measurements performed on amorphous Fe_90-xCo_xZr₁₀ alloys in the temperature range 77 K to 350 K are presented and discussed in the light of existing theoretical models. Besides unambiguously identifying weak localization, electron-phonon scattering, electron-magnon scattering and scattering of conduction electrons from spin fluctuations as main mechanisms governing the temperature dependence of within the temperature range covered in this work, the present results demonstrate that inelastic scattering of electrons from longitudinal phonons provides the most effective dephasing mechanism. Weak localization effects basically account for the negative temperature coefficient of observed for temperatures below the minimum and the inelastic scattering time or dephasing time increases rapidly with Co concentration. Spin fluctuation effects show up clearly for temperatures in the vicinity of the Curie temperature through a contribution to (T) which varies with temperature as . That spin fluctuations get suppressed by Co substitution is strongly indicated by a continuous decline of the coefficient of the term with increasing Co concentration.     

Growth and annealing effect of high-quality ZnSe:N/ZnSe by MOCVD

The ZnSe : N epitaxial layers were grown on (1 1 0) ZnSe substrates in a low-pressure metalorganic chemical vapor deposition (MOCVD) system using hydrogen as a carrier gas, and using ammonia as a dopant source. In order to obtain highly doped ZnSe : N epitaxial layers, the optimum growth and doping conditions were determined by studying the photoluminescence (PL) spectra from the ZnSe epitaxial layers grown at different ammonia flux and VI/II flux ratio. Furthermore, in order to enhance the concentration of active nitrogen in ZnSe epitaxial layer, a rapid thermal anneal technique was used for post-heat-treating. The results show that the annealing temperature of over 1023 K is necessary. Beside, a novel treatment method to obtain a smooth substrate surface for growing high quality ZnSe epitaxial layers is also described.     

Growth and MBMS studies of reaction mechanisms for InxGa1−xAs CBE

The reaction mechanism involved in the growth of In_xGa_1−xAs lattice matched to InP by chemical beam epitaxy (CBE) was investigated using growth and modulated beam mass spectrometry studies. Emphasis was placed on elucidating how variations in substrate temperature, indium composition and arsenic overpressure influence growth kinetics and how sensitive changes in experimental conditions bring about deviations in the ideal stoichiometry (In_0.53Ga_0.47As) required for lattice matching to InP. Our observations indicate that the compositional variations in the InGaAs stoichiometry at high temperatures (> 485°C) arise because of the changes in the DEG decomposition: desorption branching ratio which is controlled by a temperature- and arsenic pressure-dependent surface population of indium atoms. The low temperature behaviour is governed by the availability of metal surface sites for triethylgallium decomposition which is increased by the presence of surface indium atoms.     

Cd1−xZnxTe: Growth and characterization of crystals for X-ray and gamma-ray detectors

The choice a suitable crystal growth method and a reasonable x value is of profound importance in the preparation of high quality Cd_1−xZn_xTe crystals for x-ray and gamma-ray detectors. The present paper reviews the evolution and development of Cd_1−xZn_xTe crystal growth for x-ray and gamma-ray detectors. At the same time, emphasis is put upon finding the relationship between the x value and the quality of the Cd_1−xZn_xTe. Three sets of Cd_1−xZn_xTe ingots with different x values, specifically 0.10, 0.15, and 0.20 were grown by the vertical Bridgman method (VBM) and characterized. Their x specification was then correlated with their dislocation densities, Te precipitates, inclusions, IR transmission, resistivities, and impurity concentrations, respectively. It was found that VBM Cd_0.85Zn_0.15Te as grown in this paper possessed the best choice of qualities with respect to defects and impurities.     

MBE growth of cubic AlyGa1−yN/GaN heterostructures—structural, vibrational and optical properties

Cubic Al_yGa_1−yN/GaN heterostructures on GaAs(0 0 1) substrates were grown by radio-frequency plasma-assisted molecular beam epitaxy. High resolution X-ray diffraction, micro-Raman, spectroscopic ellipsometry, and cathodoluminescence measurements were used to characterize the structural, optical and vibrational properties of the Al_yGa_1−yN epilayers. The AlN mole fraction y of the alloy was varied between 0.07<y<0.20. X-ray diffraction reciprocal space maps demonstrate the good crystal quality of the cubic Al_yGa_1−yN films. The measured Raman shift of the phonon modes of the Al_yGa_1−yN alloy was in excellent agreement with theoretical calculations. Both SE and CL of the Al_yGa_1−yN epilayer showed a linear increase of the band gap with increasing Al-content.     

Growth and defect structure of CdF2 and nonstoichiometric Cd1?xRxF2 + x phases (R = rare earth elements and In). I. Growth of Cd1?xRxF2 + x single crystals (R = La-Lu, Y)

This article begins a series of publications on growth of single crystals of nonstoichiometric Cd_{1− x} R _x F_{2 + x} phases (R = La-Lu, Y, In) with the defect CaF₂-type structure, their crystal structures, and some properties. The present article is dedicated to the phase diagrams of the CdF₂-RF₃ systems in the region of Cd_1−x R _x F_{2 + x} formation. Their analysis shows that it is possible to synthesize homogeneous Cd_0.9 R _0.1F_2.1 crystals. The dependence of the defect structure of the crystals on the type and concentration of rare earth elements is studied on specially grown Cd_0.9 R _0.1F_2.1 (R = La-Lu) and Cd_1−x Y_xF_{2 + x} (x = 0.1, 0.15, 0.20) crystals. It is shown that, despite the fact that all the Cd_0.9 R _0.1F_2.1 crystals melted congruently, irrespectively of the rare earth elements used, they were rather homogeneous. The chemical compositions of the Cd_1−x R _x F_{2 + x} phases (R = Sm, Gd, Tb, Ho, and Lu) determined by the method of inductively coupled plasma atomic emission spectroscopy (ICP-AES) turned out to be close to Cd_0.9 R _0.1F_2.1. __________ Translated from Kristallografiya, Vol. 49, No. 3, 2004, pp. 566–574. Original Russian Text Copyright ? 2004 by Buchinskaya, Ryzhova, Marychev, Sobolev.     

Growth of Cu(AlxGa1−x)SSe pentenary alloy crystals by iodine chemical vapor transport method

Single crystals of Cu(Al_xGa_1−x)SSe pentenary alloys were successfully grown by the vapor transport technique using iodine as a transport agent. Systematic measurements of the basic crystal properties were carried out using powder X-ray, photoluminescence (PL), photoreflectance (PR), and Van der Pauw methods. Dependence of the lattice constants, exciton transition energies, and PL peak energies on Al composition, x, were examined in detail. The lattice constants obeyed Vegard's law. A quadratic dependence of exciton transition energies on x was found. The broadening parameters in the PR spectrum increase monotonically with increasing x, the results showing that the crystal quality degrades with increasing x. Exciton-related PL peaks were found for 0 ≤ x ≤ 0.77 at 77 K.