In this paper, we report on a combined modeling and experimental analysis of the GaN deposition behavior in the horizontal AIX 200/4 RF-S reactor. The study was aimed at revealing the effect of the variations of the operating parameters on the growth rate and uniformity. Variations of the trimethylgallium and hydride flow rates, changes in the composition of the mixture supplied through the hydride inlet, and the total flow redistribution between two reactor inlets have been considered. To get an insight into the mechanisms governing the measured GaN growth rate alterations, a detailed three-dimensional modeling has been used. Application of the reactor model accounting for important features of the reactor design and utilizing advanced chemical models has allowed us to reproduce fairly well experimental data and to draw conclusions on the mechanisms governing the deposition process.

The diffusion mass transfer of reagents under the conditions of local gas-phase epitaxy through a mask has been studied by the method of numerical modeling. The possible effect of adsorption of reagents on the surface of the mask and their surface diffusion on the local growth rate is studied. The computational results are compared with published experimental data.

The existence of InGaAs2 and GaAs phases in InxGa1-xAs (x similar to 0.1-0.2) have been established from Raman scattering (RS) and infra red reflectivity (IR) spectra. The evidence of partial ordering of InGaAs2 phase into [001]-(InAs)(1)(GaAs)(1) monolayer superlattice have been obtained. The measurement of the free-carrier dependence of InxGa1-xAs electron effective masses from plasmon RS revealed decreasing of the nonparabolicity of the conduction band compared with die predictions of Kein model. Growth temperature induced band gap lowering and absorption edge splitting have been observed in photoluminescence (PL) and optical absorption (OA) spectra of InxGa1-xAs. The possible origin of the observed band gap anomaly is exciton localisation at InGaAs2-phase size fluctuations.

Strained layer GaAs.95P.05 photo cathodes are presented, which emit electron beams spinpolarized to a degree of P = 75% typically. Quantum yields around QE = 0.4% are observed routinely. The figure of merit P2 × QE = 2.3 × 10−3 is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or diode lasers respectively. The cathodes are produced using MOCVD-techniques. A GaAs.55P.45-GaAs.85P.15 superlattice structure prevents the migration of dislocations from the substrate and bottom layers to the strained overlayer. The surface is protected by an arsenic layer so that no chemical cleaning is necessary before installation into vacuum. The source of polarized electrons attached to the Mainz race track microtron MAMI works with such cathodes now. More than 1000 hours beamtime have been performed successfully.

A multilayer heterostructure consisting of a GaAs/AlAs-based Bragg reflector and a GaAs cover layer was investigated. The Bragg reflector consisted of ten pairs of alternating layers of GaAs and AlAs with thicknesses of 45 and 60 nm, corresponding to the computed spectral position of the maximum of the main reflection band centered at lambda(0)=710 nm. Radiation at this wavelength is strongly absorbed in GaAs and is not absorbed in AlAs. It was determined experimentally and shown theoretically that the presence of a GaAs cover layer with optical thickness different from lambda(0)/4 on such an absorbing Bragg reflector results in the appearance of a deep dip in the region of the main reflection band. The spectral position of the dip depends on the thickness of the cover layer. If the optical thickness of the cover layer is equal to a half wavelength, then the dip lies at the center of the main reflection band. In the case where the optical thickness of the cover layer is equal to a quarter wavelength, there is no dip in the main reflection band. (C) 1996 American Institute of Physics.

plasma has been applied for high-quality, low-defect anisotropic reactive ion etching (RIE) of submicrometre scale elements in AlGaAs/GaAs heterostructures. Raman spectroscopy and photoluminescence (PL) study of the RIE-etched GaAs show no structural damage. AlGaAs/GaAs quantum well wire (QWW) structures with width 20 - 30 nm and period 250 nm were fabricated using RIE and structure preparation for overgrowth in one RIE chamber. After overgrowth by a 10 - 50 nm thick layer of AlGaAs (or GaAsP) QWW structures show the same PL intensity as initial unetched single quantum well structures.

Optical phonons of three types are seen in the Raman scattering spectra and the IR reflection spectra of the two-component solidsolutions InxGa1-xAs (x = 0.1 -0.3). The oscillator strengths S(p) and the Faust-Henry coefficients C(p) of the optical phonons of InxGa1-xAs (x almost-equal-to 0.2) are found from the Raman spectra. Analysis of the values of S(p) and C(p) and also of the polarization state in the spectra shows that optical phonons with the frequencies of transverse components, 236 and 260 cm-1, stem from vibrations of a spontaneously ordered phase. This phase has the structure of a monolayer (InAs)1(GaAs)1 superlattice in the (100) plane. The analysis also shows that the optical phonons with 267 cm-1 stem from vibrations of the GaAs phase with the zinc blende structure. The conclusion that there is a partial ordering of the InxGa1-xAs crystal lattice, accompanied by the formation of a monolayer (InAs)1(GaAs)1 superlattice, is supported by calculations of the transverse-response function in a linear-chain model. (C) 1994 American Institute of Physics.

A study has been made of how treatment in the plasma of a hydrogen glow discharge affects the photoluminescence of test samples of several types at a temperature of 78 K. The samples were layers of several compositions grown by vapor-phase epitaxy from metal-organic compounds. The layers consisted of undoped Al0.3Ga0.7As; silicon-doped Al0.28Ga0.72As (n approximately 10(17) cm-3); undoped GaAs; undoped multilayer structures with several GaAs/Al0.23 Ga0.77As quantum wells, with widths of 2, 3.6, 5.4, and 23 nm; and undoped GaAs/AlGaAs double heterostructures with separate electronic and optical confinement with a 20-nm active region. The hydrogenation reduces the photoluminescence intensity of undoped Al0.3Ga0.7As and GaAs layers, while it intensifies this luminescence in the case of silicon-doped Al0.28Ga0.72As. The photoluminescence intensity of GaAs/AlGaAs quantum wells is increased sharply by the treatment in a hydrogen plasma. The observed effect is seen most vividly in the case of narrow quantum wells. It stems from a passivation by hydrogen of radiationless defects at heterojunctions. After hydrogenation of a double heterostructure with separate confinement containing transition layers with a composition gradient near the heterojunctions, the photoluminescence spectrum of the GaAs active region becomes sharply narrower.

physica status solidi (b)Volume 178, Issue 1 p. K57-K59 Short Note Enhancement of Photoluminescence Intensity in MOCVD-Grown GaAs/AlGaAs Quantum Wells by Hydrogenation Y. A. Bumai, Y. A. Bumai Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorB. S. Yavich, B. S. Yavich A. F. Ioffe Physico-Technical Institute, St. PetersburgSearch for more papers by this authorM. A. Sinitsyn, M. A. Sinitsyn A. F. Ioffe Physico-Technical Institute, St. PetersburgSearch for more papers by this authorA. G. Ulyashin, A. G. Ulyashin Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorN. V. Shlopak, N. V. Shlopak Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorV. V. Krasovskii, V. V. Krasovskii Belorussian State Polytechnical Academy, Minsk Search for more papers by this author Y. A. Bumai, Y. A. Bumai Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorB. S. Yavich, B. S. Yavich A. F. Ioffe Physico-Technical Institute, St. PetersburgSearch for more papers by this authorM. A. Sinitsyn, M. A. Sinitsyn A. F. Ioffe Physico-Technical Institute, St. PetersburgSearch for more papers by this authorA. G. Ulyashin, A. G. Ulyashin Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorN. V. Shlopak, N. V. Shlopak Belorussian State Polytechnical Academy, Minsk Search for more papers by this authorV. V. Krasovskii, V. V. Krasovskii Belorussian State Polytechnical Academy, Minsk Search for more papers by this author First published: 1 July 1993 https://doi.org/10.1002/pssb.2221780137 F. Skaryna ave. 65, 220027 Minsk, Republic of Belarus. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume178, Issue11 July 1993Pages K57-K59 RelatedInformation

An investigation was made of the dependence of the efficiency of spontaneous emission from the active region and barrier layers on the current density in AlGaAs/GaAs quantum-well laser diodes. The main reasons for the increase in the threshold current density and reduction in the differential efficiency of laser diodes characterized by large output losses were an increase in the proportion of nonequilibrium carriers recombining in the waveguide layers and the process of electron leakage to the p-type emitter.

The paper reports on theoretical and experimental studies of the threshold current density and differential quantum efficiency dependencies on output losses for AlGaAs/GaAs and InGaAsP/GaAs SQW SCH laser diodes. A theoretical model is proposed to calculate the effect of waveguide recombination and leakage to the cladding on the threshold current and differential quantum efficiency of SQW SCH lasers. It is shown that the model assuming quasineutrality and continuity of quasi Fermi levels at interfaces gives a correct description of the process of carrier recombination in the waveguide layers of the lasers in question. Carrier leakage from the active region should be the main cause of increase of the threshold current density in the SQW lasers for densities in excess of ∼3 kA/cm2. It has been established that the carrier concentration in the waveguide increases above the lasing threshold as well, which can result in enhanced leakage into the claddings with increasing current density and to an anomalous decrease of differential efficiency in short‐cavity laser diodes for structures with small (≲100 meV) bandgap difference between the waveguide and cladding layers. The experimentally revealed decrease of the differential efficiency in short‐cavity diodes is essentially faster than that predicted by the model. One of possible causes of the decrease of differential efficiency is the enhanced filamenttion of lasing with decreasing cavity length.

The problem of increasing the lifetime of GaAs/AlGaAs double heterostructure (DHS) laser stimulated a wide range of publications concerning with the study of degradation processes.1-6 On the whole, at present a certain understanding of the problem has been achieved. It was shown in Refs. 1-3 that the processes of recombination-enhanced dislocation climb (REDC) and recombination-enhanced dislocation glide (REDG) may dominate in the rapid degradation phenomenon. Dislocation climb requires the motion of intrinsic point defects, while the dislocation glide occurs mainly due to local stress or local heating as a result of nonradiative recombination. The role and the origin of point defects which participate in the dislocation climb process is not understood yet. There are two models of defect generation: extrinsic and intrinsic.1.3 The first model assumes that V(Ga) and V(As) are produced in the dislocation core at an equal rate during REDC. The second model requires the absorption of existing point defects (As interstitials) at a dislocation and the generation of antisite defects As(Ga), Ga(As), V(Ga) during REDC of dislocation. A heterointerface may be probably viewed as a source of large concentration point defects. 2,7,8 Interface defects may be generated due to a local stoichiometry variation during the growth of a heteroepitaxial layer.2.7 The processes of heterostructure laser degradation are usually investigated by transmission and scanning electron microscopy techniques. Dark line defects (DLD), which form at a rapid laser degradation and which are the centers of nonradiative recombination, are observed by an electron probe induced current technique.