ESTIMATION OF THE STRAIN STATE OF GEXSI1-X/SI STRAINED-LAYER SUPERLATTICES BY DOUBLE-CRYSTAL X-RAY-DIFFRACTION

20-period strained-layer superlattices of nominal composition and width Ge0.2Si0.8 (5 nm)/Si(25 nm) and Ge0.5Si0.5 (5 nm)/Si(25 nm) were studied by double-crystal X-ray diffraction. The Ge content x was determined by computer simulation of the diffraction features from the superlattice. This method is shown to be independent of the relaxation of the superlattice. Alternatively, x can be obtained from the measured difference DELTAa/a in lattice spacing perpendicular to the growth plane. It is sensitive to the relaxation. Comparing the results obtained in these two different ways, information about the relaxation of the superlattices can be obtained.

GROWTH OF WIDE-BAND GAP IMMISCIBLE II-VI ALLOYS BY METALORGANIC VAPOR-PHASE EPITAXY

Although metalorganic vapor phase epitaxy (MOVPE) is generally regarded as a non-equillibrium process, it can be assumed that a chemical equilibrium is established at the vapor-solid interface in the diffusion limited region of growth rate. In this paper, an equilibrium model was proposed to calculate the relation between vapor and solid compositions for II-VI ternary alloys. Metastable alloys in the miscibility gap may not be obtained when the growth temperature is lower than the critical temperature of the system. The influence of growth temperature, reactor pressure, input VI/II ratio, and input composition of group VI reactants has been calculated for ZnSSe, ZnSeTe and ZnSTe. The results are compared with experimental data for the ZnSSe and ZnSTe systems.

GROWTH OF GASB AND GAASSB IN THE SINGLE-PHASE REGION BY MOVPE

GaSb layers are grown on GaSb substrates; the effects of input partial pressure of trimethylantimony and the V/III ratio are studied. A model of the MOVPE phase diagram for the growth of GaSb and GaAsxSb1-x is developed which assumes thermodynamic equilibrium to be established at the solid-vapor interface.

CBE GROWTH OF GAAS/GAAS, GAAS/SI AND ALGAAS/GAAS USING TEG, ASH3 AND AMINE-ALANE PRECURSORS

The growth of high quality AlGaAs by CBE bas been limited by the high levels of carbon and oxygen contamination. The use of alane based precursors offers a significant reduction in such contamination. We report for the first time the CBE growth of AlxGa1-xAs from triethylgallium, dimethylethylamine-alane and arsine, and compare with. growth from triethylgallium, trimethylamine-alane and arsine. Some preliminary results of work on the CBE growth of GaAs on silicon will also be reported.

Stoichiometric defects in semi-insulating GaAs

The influences of arsenic interstitials and dislocations on the lattice parameters of undoped semi-insulating (SI) GaAs single crystals were analyzed. It was shown that the dislocations in such crystals serve as effective gettering sites for arsenic interstitials due to the deformation energy of dislocations. The average excess arsenic in GaAs epilayers grown by molecular-beam epitaxy (MBE) at low temperatures (LT) is about 1%, and the lattice parameters of these epilayers are larger than those of liquid-encapsulated Czochralski-grown (LEG) SI-GaAs by about 0.1%. The atomic ratio, [As]/([Ga] + [As]), in SI-GaAs grown by low-pressure (LP) LEC is the nearest to the strict stoichiometry compared with those grown by high-pressure (HP) LEC and vertical gradient freeze (VGF). After multiple wafer annealing (MWA), the crystals grown by HPLEC become closer to be strictly stoichiometric.

Phase diagrams for the MOVPE growth of ZnTe and ZnSeTe

The phase diagrams for the MOVPE growth of ZnTe and ZnSeTe have been proposed for the first time, based on the thermodynamic equilibrium established at the solid-vapor interface, The regions for the single condensed phase of ZnTe(s) and of ZnSeTe(s) have been investigated, respectively, Additionally, the growth conditions of appearance for the double condensed phase of ZnTe(s) + Zn(s or l) and ZnTe(s)+ Te(s or l) for the ZnTe system, of ZnSeTe(s) + Zn(s or l) and ZnSeTe(s)+ Te(s or l) for the ZnSeTe system are discussed.

GSMBE growth and PL investigation of lattice-matched InGaAs/InP quantum wells

Using a home-made gas-source molecular beam epitaxy system, high quality InGaAs quantum wells with different well widths lattice-matched to a (001) InP substrate have been obtained. Sharp and intense peaks for each well can be well resolved in the PL spectra for the sample. For well widths larger than similar to 60 Angstrom, the exciton energies are in good agreement with those of calculation. For wells narrower than 40 Angstrom, our line widths are below the theoretical values of line width broadening due to one monolayer interface fluctuation, showing that the interface fluctuation of our sample is within one monolayer.

GROWTH INTERRUPTION INDUCED INTERFACE MICROROUGHNESS IN SINGLE QUANTUM-WELLS

Growth interruption-induced microroughness is studied by photoluminescence (PL) of single quantum wells with different well widths and interruption times. Analysis of the peak splitting in the PL spectra shows that the adjacent peak splittings correspond to well width differences smaller than one monolayer. The number of split peaks increases with increasing well width, saturating when the well width exceeds 11 monolayers. This trend correlates well with the decrease in the lateral dimension of the exciton, which corresponds roughly to the minimum optically sampled area of the interface. For a given quantum well, a plot of the normalized integrated intensities of the split PL peaks versus the well width fluctuation is well described by a Gaussian distribution with an average fluctuation smaller than one monolayer. These results are consistent with the microroughness model.

BACKGATING AND LIGHT SENSITIVITY IN GAAS METAL-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS

Three different types of GaAs metal-semiconductor field effect transistors (MESFET) by employing ion implantation, molecular beam epitaxy (MBE) and low-temperature MBE (LT MBE) techniques respectively were fabricated and studied in detail. The backgating (sidegating) measurement in the dark and in the light were carried out. For the LT MBE-GaAs buffered MESFETs, the output resistance R(d) and the peak transconductance g(m) were measured to be above 50 k Omega and 140 mS/mm, respectively, and the backgating and light sensitivity were eliminated. A theoretical model describing the light sensitivity in these kinds of devices is given. and good agreement with experimental data is reached.

Chemical etching of a GaSb crystal incorporated with Mn grown by the Bridgman method under microgravity conditions

A GaSb crystal incorporated with Mn has been grown by the Bridgman method on the Polizon facility onboard the FOTON-M3 spacecraft. Structural defects and growth striations have been successfully revealed by the chemical etching method. By calculating various parameters of the convection, the striation patterns can be explained, and the critical value of the Taylor number, which characterizes the convective condition of the rotating magnetic field induced azimuthal flow, was shown. The stresses generated during crystal growth can be reflected by the observations of etch pit distribution and other structural defects. Suggestions for improving the space experiment to improve the quality of the crystal are given.

Growth and photoluminescence of InAlGaN films

Two quaternary InAlGaN films were grown by metal-organic chemical-vapor deposition (MOCVD) on sapphire (0001) substrates with and without high-temperature GaN interlayer, respectively. The structural and optical properties of the quaternary films were investigated by high-resolution X-ray diffraction (HRXRD), high-resolution electron microscopy (HREM), temperature-dependent photoluminescence (PL) spectroscopy and time-resolved photoluminescence (TRPL) spectroscopy. According to the HRXRD and PL results, it is demonstrated that two samples have the same crystal quality. The TRPL signals of both samples were fitted well as a stretched exponential decay from 14 K to 250 K, indicating significant disorder in the materials, which is attributed to recombination of excitons localized in disorder quantum nanostructures such as quantum dots or quantum disks originating from indium (In) clusters or In composition fluctuation. The cross-section HREM measurement further proves that there exist disorder quantum nanostructures in the quaternary. By investigating the temperature dependence of the dispersive exponent beta, it is shown that the stretched exponential decays of the two samples originate from different mechanisms. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Space-grown SI-GaAs and its application

A semi-insulating GaAs single crystal ingot was grown in a recoverable satellite, within a specially designed pyrolytic boron nitride crucible, in a power-travelling furnace under microgravity. The crystal was characterized systematically and was used in fabricating low noise field effect transistors and analogue switch integrated circuits by the direct ion-implantation technique. All key electrical properties of these transistors and integrated circuits have surpassed those made from conventional earth-grown gallium arsenide. This result shows that device-grade space-grown semiconducting single. crystal has surpassed the best. terrestrial counterparts. Studies on the correlation between SI-GaAs wafers and the electronic devices and integrated circuits indicate that the characteristics of a compound semiconductor single crystal depends fundamentally on its stoichiometry.

Twin and grain boundary in InP: A synchrotron radiation study

Experimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.

High-quality metamorphic HEMT grown on GaAs substrates by MBE

Metamorphic high electron mobility transistor (M-HEMT) structures have been grown on GaAs substrates by molecular beam epitaxy (MBE). Linearly graded and the step-graded InGaAs and InAlAs buffet layers hal e been compared, and TEM, PL and low-temperature Hall have been used to analyze the properties of the buffer layers and the M-HEMT structure. For a single-delta-doped M-HEMT structure with an In0.53Ga0.47As channel layer and a 0.8 mum step-graded InAlAs buffer layer, room-temperature mobility of 9000 cm(2)/V s and a sheet electron density as high as 3.6 x 10(12)/cm(2) are obtained. These results are nearly equivalent to those obtained for the same structure grown on an InP substrate. A basic M-HEMT device with 1 mum gate was fabricated, and g(m) is larger than 400 mS/mm. (C) 2001 Elsevier Science B.V. All rights reserved.