Planes Of GaAs Research Articles

Dislocation dynamics in anisotropic piezoelectric crystals. III. Elliptical dislocation loop

Abstract A line integral expression for the electric field around a uniformly moving elliptical dislocation loop in anisotropic piezoelectric crystals is derived from the Fourier integral expression which was given in the authors' previous (1985) paper. Numerical integrations are carried out for the electric fields generated by an elliptical dislocation loop which lies on the close-packed plane in GaAs.

Electronic structure of an InAs monomolecular plane in GaAs.

The electronic structure of an InAs monomolecular plane in the host GaAs is calculated by a self-consistent pseudopotential method. In this monomolecular-plane--host-crystal system, both electrons and holes are found to be strongly localized near the inserted InAs plane. The inserted InAs plane behaves somewhat like a quantum well. This result successfully explains the observed intense photoluminescence spectra. We also calculate the band structure for a system of two InAs monomolecular planes separated by N monolayers of GaAs. The calculated band gap as a function of GaAs thickness between the two InAs planes is in good agreement with experimental data.

Structure of (111) CdTe epilayers on misoriented (001) GaAs

Results concerning [111]CdTe growth on misoriented (001) GaAs substrates are presented and discussed. Growing CdTe on GaAs substrates with Ga steps results in twin-free layers, which is not the case for As steps. The tilt of the (111) CdTe planes with respect to the (001) GaAs planes is reported versus the GaAs substrate misorientation. We propose a model that establishes a correspondence between the measured tilt and the presence of interface dislocations as observed by high-resolution electron microscopy. This model also takes into account the effects of the surface morphology on the suppression of twins.

Tem Study of the Structure of Mbe GaAs Layers Grown at Low Temperature

ABSTRACTThe structural quality of GaAs layers grown at 200°C by molecular beam epitaxy (MBE) was investigated by transmission electron microscopy (TEM). We found that a high crystalline perfection can be achieved in the layers grown at this low temperature for thickness up to 3 μm. In some samples we observed pyramid-shaped defects with polycrystalline cores surrounded by microtwins, stacking faults and dislocations. The size of these cores increased as the growth temperature was decreased and as the layer thickness was increased. The upper surface of layers with pyramidal defects became polycrystalline at a critical thickness of the order of 3μm. We suggested that the low-temperature GaAs becomes polycrystalline at a critical thickness either because of a decrease in substrate temperature during growth or because strain induced by excess As incorporated in these layers leads to the formation of misoriented GaAs nuclei, thereby initiating polycrystalline growth. The pyramidal shape of the defects results from a growth-rate hierarchy of the low index planes in GaAs.

Structural characterization of AlGaAs/GaAs multiquantum-well structures grown on silicon

Abstract AlGaAs/GaAs multiquantum-well (MQW) structures deposited on Si(001) substrates misoriented by 4° toward 〈110〉 have been fabricated by molecular beam epitaxy (MBE) and a combination of organo-metallic chemical vapour deposition (OMCVD) and MBE. Such structures are of great interest for a better understanding of the growth of III–V compounds on misoriented silicon substrates. We have grown structures with 100 or 150 periods of GaAs wells 80 A thick and Al 0.25 Ga 0.75 As barriers 150 A thick. These structures have been studied by X-ray double crystal diffraction (DCD) and compared with those grown on GaAs substrates. We observe: (a) a tilt of the (001) planes of MQW and GaAs with respect to (001) silicon planes in the range of 0.04–0.2°. This is attributed to the initial misorientation of the silicon substrate and the 4% lattice mismatch between GaAs and silicon; (b) a perpendicular strain (ϵ⊥) of about −10 −3 corresponding to a stress parallel to the (σ∥) of about 2 × 10 8 Pa. This observation is related to the difference of thermal expansion coefficients of GaAs/AlGaAs and silicon, acting when the sample is cooled to room temperature; (c) a defect density in the range of 10 6 −10 7 cm −2 ; (d) in the best case; a full width at half maximum of the satellite peaks three times wider than those measured on GaAs substrates; (e) a misorientation of the MQW with respect to the (001) GaAs planes of about 3° toward 〈110〉 direction. The crystalline and stacking quality of the MQW structures are checked with scanning transmission electron microscopy (STEM) studies.

Electron and Positron Distribution for the Plane (1110) in Si and GaAs

AbstractThe electron and positron charge densities are calculated as a function of position in the unit cell for two diamond and zincblende semiconductors, using wave functions derived from nonlocal pseudopotential band structure calculations for the electronic part, and the positron wave functions are calculated for single‐particle approximation in manner which is free of any theoretical assumptions.

Electron counting model and its application to island structures on molecular-beam epitaxy grown GaAs(001) and ZnSe(001).

The principal reconstructions found on the low-index planes of GaAs and ZnSe can be explained in terms of a simple electron counting model. A surface structure satisfies this model if it is possible to have all the dangling bonds on the electropositive element (Ga or Zn) empty and the dangling bonds on the electronegative element (As or Se) full, given the number of available electrons. This condition will necessarily result in there being no net surface charge. The justification for this model is discussed. The GaAs(001)-(2\ifmmode\times\else\texttimes\fi{}4) reconstruction is known to involve surface dimers. It is shown that a (2\ifmmode\times\else\texttimes\fi{}4) unit cell with three dimers and one dimer vacancy is the smallest unit cell that satisfies the electron counting model for this surface. The electron counting model is used to explain the structure of islands imaged by scanning tunneling microscopy on the GaAs(001)-(2\ifmmode\times\else\texttimes\fi{}4) surface. The model shows that island structures built up from complete (2\ifmmode\times\else\texttimes\fi{}4) unit cells can be stable if they extend in the 2\ifmmode\times\else\texttimes\fi{} direction, but not if they extend in the 4\ifmmode\times\else\texttimes\fi{} direction. These island structures can also provide an explanation for the different step structures seen on GaAs(001) vicinal surfaces. Much less is known experimentally about step and island structures on ZnSe(001). Structures on this surface predicted by the electron counting model differ significantly from those found on GaAs(001).

InAs monomolecular plane in GaAs grown by flow-rate modulation epitaxy

InAs monomolecular planes are grown in GaAs by flow-rate modulation epitaxy. This structure exhibits low-temperature (2 K) photoluminescence with high intensity and a small linewidth. Two InAs planes separated by N monolayers of GaAs also exhibit intense, narrow photoluminescence. The peak photon energies drastically increase with the distance between the planes. Assuming that an InAs plane in GaAs forms a 1-monolayer-thick InAs/GaAs quantum well, the photoluminescence peak photon energies and the drastic increase are explained using a finite square well model.

The formation of microsplits and damage rafts in proton-bombarded GaAs

The technique of cross-sectional transmission electron microscopy has been used to study the nature and formation of damage rafts, which act as dislocation sources, in proton-bombarded (5×1015, 1016 and 1017 H+ cm−2) and annealed GaAs. The results show that the rafts consist of a planar array of voids lying on the {110} cleavage planes of GaAs. The dislocations generated at these rafts are glissile, of the (a/2) 〈110〉 type, and glide on the {111} planes intersecting the rafts. Models are presented to show that these damage rafts originated at microsplits on the {110} cleavage planes of GaAs following the cracking open of small hydrogen-filled platelets on {110} planes when the internal gas pressure exceeds that which is necessary for crack propagation. From the analysis of the results an average diffusion length of ∼1 μm was estimated for vacancies in proton-bombarded GaAs at ∼900° C.

New Approach to Growth of High-Quality GaAs Layers on Si Substrates

AbstractGaAs layers were grown on Si (001) substrates by molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). They were examined by transmission electron microscopy, doublecrystal X-ray diffraction and Rutherford backscattering/channeling technique. Initial layer growth in both MEE and MBE was governed by three-dimensional nucleation but a stronger tendency for GaAs islands to align along the surface steps of Si was observed in the case of MEE. There was no measurable tilt between the (001) planes of GaAs and Si if growth was initiated by MEE at low temperature, prior to further growth by MBE at higher temperatures. On the contrary, the tilt angle was 0.34• when the entire structure was prepared by conventional two-step MBE. Rutherford backscattering measurements indicated a significant reduction in the density of defects throughout MEE/MBE GaAs in comparison with MBE GaAs.

REM and RHEED investigation of the epitaxy of evaporated gold film on a CaAs (110) surface

Detailed understanding of the epitaxial grown gold thin film is highly desirable, both for fundamental physical reasons and due to increasingly sophisticated applications. In this paper, we present the utilization of the significant advantages of both REM and RHEED in a commercial Philip-400T instrument to investigate the crystalline quality and topography of epitaxical gold layers on GaAs(110) surfaces.The specimen preparation was carried out in a commercial FC-12E UHV system containing a quartz crystal sensor for thickness control. The experimental arrangement inside the UHV chamber is shown in Fig. 1, where the evaporating source is set in a position equally distance from the crystal sensor and the specimen substrate. The bulk shield next to the specimen is to block a part of the gold flux, thus the growing film with a certain variation of thickness can be formed on the GaAs (110) plane which faces the shield.

DLTS investigations of UHV prepared n-GaAs(110)-Au Schottky diodes

Deep level transient spectroscopy (DLTS), capacitance-voltage ( C- V) and current-voltage ( I- V) techniques are employed to investigate ultrahigh-vacuum (UHV) prepared n-GaAs(110)-Au Schottky diodes. These diodes are prepared on cleavage planes of GaAs (LEC) by evaporation of Au in UHV. All subsequent measurements are performed without breaking the UHV. Samples with “ideal” surfaces show no detectable amount of deep traps (less than 10 13 cm −3). Samples with stepped surfaces show a deep electron trap 0.3 eV below E C ( N T = 2 × 10 15 cm −3) with characteristics of the EL6-center.

Identification of hydrogen platelets in proton-bombarded GaAs

The technique of cross-sectional transmission electron microscopy has been applied to study the nature of the radiation damage in GaAs bombarded with 300 keV protons to total doses of 1015 and 5×1015 protons cm−2. The results indicate that upon annealing at temperatures of 500 °C and above, the precipitated damage becomes visible in the form of hydrogen platelets (i.e., hydrogen-filled edge vacancy loops) on the {110} cleavage planes of GaAs.

Growth of molybdenum and tungsten on GaAs in a molecular beam epitaxy system

Thin films of Mo and W were grown on top of (100) GaAs in a molecular beam epitaxy system. Mo grew epitaxially between 200 and 450 °C with its (111) plane parallel to (100) GaAs plane. W grew as a random polycrystalline deposit. For both metals, interaction with the GaAs occurred during growth at 500 °C. Schottky barrier heights determined by current and capacitance measurements show that the electrical properties of the metal-GaAs interface do not strongly depend on the growth temperature and the microstructure of the films.

Photoluminescence of CdTe: A comparison of bulk and epitaxial material

Photoluminescence (PL) studies of bulk and epitaxial CdTe samples obtained from several sources are discussed. Steady state PL measurements were carried out at temperatures ranging from 16–300 K. The effects of surface preparation, substrate temperature, and film thickness were studied in detail for homoepitaxial films grown on the (111)A and (100) planes of CdTe. PL studies of epitaxial CdTe films grown on (0001) sapphire by molecular beam epitaxy (MBE), by hot wall MBE, and by metal-organic chemical vapor deposition (MOCVD), and on the (111)B and (100) planes of GaAs by MBE have also been completed. The CdTe epilayers on sapphire and GaAs substrates typically display a bright PL spectrum dominated by the near edge peak at 1.58 eV (77 K). In addition, a number of films exhibit a near edge peak at 1.503 eV at 300 K, which is indicative of high quality epitaxy and which allowed direct measurement of the room temperature band gap of CdTe. PL studies of epitaxial Cd1−x MnxTe films grown by MBE on 5.0 μm thick CdTe buffer layers on GaAs substrates reveal shifts of the band gap into the visible spectral region with increasing x accompanied by a significant increase in edge peak magnitude.

AN ELECTRON SPECTROSCOPY STUDY OF THE In/GaAs (111) INTERFACE FORMATION PROCESS

The interface formation process for In deposited on noncleaved GaAs (111) plane has been studied by means of photoemission speetroscopy combined with LEED pattern analysis. It is shown that the growth of three-dimensional In clusters dominates in this process. The surface Fermi level is found at 0.75±0.05 eV above VBM for all the investigated n-type samples prior to the deposition of In: these include both Ga-terminated GaAs(lll)-A and Asterminated GaAs (lll)-B faces. The Fermi level rapidly shifts to 0.90±0.05 eV above VBM during the deposition of In.

The surface energy of Si, GaAs, and GaP

The surface energy of various planes in Si, GaAs, and GaP was measured by the use of a modified spark discharge method, previously used successfully in metals. Surface energy values were determined for the following cleavage planes in these crystals: Si {111}∼1.14 J/m2, Si {110}∼1.9 J/m2, GaAs {110}∼0.86 J/m2, and GaP {110}∼1.9 J/m2. The Si surface energy value was compared with previous experimental measurements. The Si {110}, GaAs {110}, and GaP {110} values were compared only to theoretical estimations, since as far as it is known, the surface energy of these planes have never been measured experimentally. Berg-Barrett x-ray topography and chemical etch pit analysis verified that plastic relaxation did not occur under the test conditions used. The cleavage surface energies determined in this work were in good agreement with previous theoretical estimations. Experimental observations confirmed a lack of plastic energy dissipation and a stability of cleavage propagation which indicated that the measured surface energies were close to the intrinsic values.

Focusing Effects of Surface Acoustic Waves in Crystalline Solids

Focusing of surface acoustic waves (SAW) due to elastic anisotropy of substrate crystals is investigated theoretically. For propagation on the (001) plane of GaAs, we find strong focusing effects of the SAW along certain directions. We also find that the number of independent pure-mode axes lying in the focusing directions is just one on the (001) surface.

Electron-microscope study of 10.6-μm laser damage in GaAs

The nature of the damage to GaAs caused by exposure to a 10.6-μm laser beam at power densities of 1130, 2260, and 5650 W/cm2 was determined by transmission electron microscopy. At 5650 W/cm2 damage was observed at the surface in the form of craters of 80 μm or larger in diameter. Within the craters were found concentric zones spreading out from the center and consisting of (1) an amorphous region, (2) a region showing striations and skeletal crystalline walls in an amorphous matrix, and (3) a mixed amorphous-crystalline region containing small rounded clusters of dislocations, some of which were helical. In one case crystalline arsenic was found near the central zone. The results observed at this power level indicate that thermal effects have caused melting, evaporation, and decomposition. It is suggested that the skeletal walls and the striations parallel to {110} planes are caused by preferential evaporation or decomposition and may be related to the presence of small precipitates or chemical inhomogeneities along {110} planes of GaAs as observed by others. Damage near the entrance surface at low power densities, and at the exit surface for the highest power density, consisted of unique clusters of dislocations spreading out along orthogonal 〈110〉 directions up to 3 μm. Although the direct cause of these dislocations could not be determined, it suggested that they result from cracking or cleavage of the crystal due to stresses caused by localized heating at sites of precipitates, occlusions, or other faults in the crystal.

Etch Pit Observation of Very Thin {001}-GaAs Layer by Molten KOH

The etching rate on a {001} plane of GaAs in molten KOH as the etchant is examined in order to reveal etch pits corresponding to dislocations for thin GaAs layers. The mean etching rates were 0.083 µm/min. and 0.98 µm/min. at 300°C and 350°C, respectively. It was found that the etching thickness of about 0.3 µm was sufficient to reveal the dislocation structure. This etching method using molten KOH is applicable to the examination of the correlation between dislocations in epitaxially grown thin layers and those in the substrates. Most dislocations propagate from the substrate to the epitaxial layers, whereas some parts of dislocations disappear in the epitaxial layers and the others are generated in the epitaxial layers.