The growth of metals and semiconductors on reconstructed semiconductor surfaces proceeds through a number of conceptually distinct stages. These include: 1) the growth of the first layer or layers, which may have different reconstructions as growth proceeds; 2) the growth of (2D or 3D) islands of the deposit, and/or by step flow; 3) coalescence and/or coarsening of islands and/or the introduction of defects such as dislocations. Of particular interest are cases when the different ‘stages’ are in competition with each other, i.e. they constitute alternative sinks for (and sources of) arriving and migrating adatoms. The development of rate equations to describe such situations, and extract relevant atomic parameters, is outlined. Experimental examples are taken from recent work on Ag and Ge deposits on Si( 111) and (100) surfaces.

An important role of type SB step edges in determining the as-grown microstructure of Si-Ge superlattices and alloys is implicated from direct Z-contrast images of as-grown structures. A variety of different ordered phase variants can arise at each Si on Ge interface as a result of vertical segregation during superlattice growth. A new monoclinic-ordered structure is predicted to arise as a result of lateral segregation during alloy growth.

Deliberate introduction of a surfactant can drastically influence the growth mode of germanium on silicon. Without a surfactant germanium growth proceeds in a typical Stranski-Krastanov mode. The system is minimizing its built-in energy by undergoing strain relaxation through a clustering mechanism (islanding). In all surfactant-mediated growth processes it was possible to obtain smooth layers without island formation. The influence of different ways for introducing the surfactant layer (at the interface between substrate and growing film, in the growing film below the critical Stranski-Krastanov thickness, or on top of the grown Ge film) will be presented. Especially in surfactant-controlled solid phase epitaxy (SPE) the smooth epitaxial germanium layer was obtained by passing through an island formation stage. These islands formed below 400 °C are of different structure than the ones formed without a surfactant. Possible mechanism for the “smoothing out” of islands developed in the beginning stage of surfactant-controlled SPE will be proposed. The island formation stage can be completely suppressed by depositing the surfactant on top of the amorphous Ge layer before increasing the temperature.

Transmission electron microscopy and photoluminescence studies were performed to determine the critical thickness for generation of misfit dislocations in Sil-xGex layers grown by low pressure chemical vapor deposition. Above a certain Ge content the transition from two dimensional to three-dimensional growth occurs before generation of misfit dislocations. For instance, for x ∼0.3 and a substrate temperature around 700°C island formation was observed to start at 1.8 nm. The formation of islands is attributed to the preferential growth of SiGe in areas with less lattice strain. Islands were observed to broaden the exciton photoluminescence of the quantum well structures.

The nucleation of epitaxial transition-metal nitride films with different lattice mismatch and growth of the corresponding supcrlattices were studied. In-situ Auger electron spectroscopy (AES) was used to characterize the nucleation mechanisms of V0.3Nb0.7N films on TiN (1.7% mismatch), TiN films on VN (2.4% mismatch), TiN films on NbN (3.6% mismatch), NbN films on VN (5.7% mismatch), and VN films on NbN grown by ultra-high vacuum reactive magnetron sputtering. The initial growth mechanism was layer-by-layer for mismatch values up to 3.6%, but three-dimensional island nucleation occurred for 5.7% mismatch. Scanning tunneling microscopy (STM) observations of NbN films showed threedimensional islands, confirming the AES results. X-ray diffraction spectra from the corresponding superlattices showed strong superlattice reflections except for the large-mismatch NbN/VN combination. Cross-sctional transmission electron microscopy studies showed that the superlattice layers were.velldefined and planar for low mismatch, but were irregular and non-planar for VN/NbN, in agreement with the X-ray, AES, and STM results. The maximum lattice mismatch for epitaxial nitride superlattice growth was thus limited by island nucleation and in the range from 3.6 - 5.7%.

We have investigated the molecular beam epitaxial growth of homoepitaxial InAs and GaSb and InAs/GaSb heterostructures on both the (111)A and (111)B orientations. Our studies have found that high quality GaSb epilayers can be grown on both the (111)A and (111l)B orientations over a wide range of growth temperatures and flux ratios. Reflection high energy electron diffr-action phase diagrams for GaSb [111[ are presented. InAs/GaSb heterostructures, simultaneously grown on (11l)A and (111)B orientations, have been investigated by secondary ion mass spectroscopy depth profiles and double crystal x-ray diffraction. Unintentional incorporation of the ‘second’ group-V element is found to be approximately three times greater in the (111)A orientation than in the (111)B for both species.

The initial stages of epitaxial growth of laser ablated YBa2Cu3O7-δ (YBCO) thin films on (001) SrTiO3, LaAlO3, and MgO substrates, and on slightly miscut LaA1O3 and SrTiO3, have been studied with scanning tunneling microscopy (STM). Surface images show that the initial YBCO growth mode can be either of the Stranski- Krastanov or the Volmer-Weber type, depending on the film-substrate lattice mismatch and the growth temperature. A small substrate miscut angle is found to strongly influence the growth mode of YBCO films. Screw dislocation-mediated growth is suppressed, and films grown at 800°C on (001) LaAlO3 substrates with miscut angle of 2.0° along <100> or <110> directions were found to consist of tilted platelets that are epitaxially aligned with the substrate crystal lattice.

An impurity adsorption model is proposed accounting for a distortion of the surface morphology of GaAs:Be epitaxial layers and an emergence of misoriented facets. According to the model, the morphology distortion occurs as the surface sublimation energy of the growing face drops down to zero because of adsorption of Be atoms at the layer surface. The model is in good agreement with available experimental data on the surface morphology distortion of GaAs:Be layers grown by MBE.

The room temperature chemisorption of disilane on Ge(100) and subsequent reaction at elevated temperatures was investigated by core level photoemission spectroscopy. At room temperature Si2H6 chemisorbs dissociatively on Ge(100) forming a surface populated largely by Si-H groups. Annealing the sample to 300°C effectively reduces the Si-H species to elemental Si. An additional anneal to 580°C promotes the diffusion of Si into the bulk and restores the Ge surface to an atomically clean state.

The growth of CuCl/CaF2 heterostructures has been studied with an atomic force microscope (AFM). We have grown by molecular beam epitaxy (MBE) CuCl thin films at various substrate temperatures and thicknesses on CaF2(111) substrates. AFM studies reveal that islanding is the dominant growth mechanism. We calculated the height-height correlation function, 〈lh(qt)|2〉, for each of our films and compared them to the predictions made by the Shadowing Growth Theory, a preexisting growth model that enabled us to extract the important kinetic parameter of surface diffusion length for the growth condition of each of the four films.

The growth of high quality Si/GaAs superlattices on GaAs substrates using molecular beam epitaxy is described. A typical superlattice structure consisted of ten periods of thin (<5Å) layers of pseudomorphic silicon alternating with thick GaAs layers; typical GaAs thicknesses range from 100Å to 1850Å. In situ reflection high energy electron diffraction analysis of the structures during growth showed the silicon layers developed a (3 ×1) reconstruction, while the GaAs exhibited a (4×2)→(3×2)→(3×1)→(2×4) reconstruction sequence. Both observations agree with prior studies of the growth of embedded silicon in GaAs/Si/GaAs heterostructures. X-ray diffraction using the (004) reflection showed sharp and intense satellite peaks (out to 22 orders in one case), indicating a high level of structural quality. Very good agreement has been obtained between observed diffraction patterns and those calculated via dynamical simulation.

Reflection High Energy Electron Diffraction (RHEED) oscillations under arsenic and gallium-controlled Molecular Beam Epitaxy (MBE) growth conditions have been used to measure the sticking and desorption coefficients of As2 and As4. The coefficients are obtained from measurements of the arsenic incorporation rates. Comparisons are made with measurements obtained from desorption rates using modulated beam mass spectroscopy. The transition from gallium to arsenic-controlled growth is observed to occur after excess gallium atoms accumulate on the surface. The maximum intrinsic arsenic sticking coefficients occur when the maximum number of gallium atoms can be incorporated for a given arsenic flux. The intrinsic maximum arsenic sticking coefficients are found to be 0.75 and 0.50 for As2 and As4, respectively. During galliumcontrolled growth, the arsenic sticking coefficients are independent of substrate temperature as long as the sticking coefficient of gallium is equal to one. However, a temperature dependent maximum gallium-controlled arsenic sticking coefficient exists. It can be measured by the maximum Ga to As4 flux ratio that produces specular film surfaces. During gallium-controlled growth, the Ga to As flux ratios are shown to be equal to the gallium-controlled arsenic sticking coefficients. The activation energy for arsenic desorption during arsenic-controlled growth conditions was measured as -0.50 eV for independent As4 and As2 incident fluxes. During gallium-controlled growth with incident As4 fluxes, an activation energy for arsenic desorption of -0.70 eV was measured for the maximum gallium-controlled arsenic sticking coefficients.

In this work we investigate the initial stages of growth of heteroepitaxial films of InAs on semi-insulating InP substrates using MOCVD. Very thin films grown at different temperatures, Tn, were studied using TEM and SEM. The 3.2% lattice mismatch between InAs and InP causes strains that are partially accomodated by the generation of misfit dislocations at the interface. Our studies indicate that the deposited InAs nucleates in the form of islands which then grow and coalesce to form the film. Elemental mapping studies indicate that the area of substrate covered by the film is a function of the growth temperature. The thickness of the film and the electron mobilities also vary with T°. The films with best mobilities were obtained for Tn = 480°C.

By Pulsed Gas CVD-growth, heteroepitaxial growth of pure Ge-layers from pure GeH4 has been accomplished at 650 °C on Si-substrates without intermediate Si1−xGex-bufferlayers. The material has been studied by means of RBS, SEM, ECP, XRD and cross-sectional, highresolution and plan-view TEM. The thickness of the Ge-layers varied between 2 and 24 monolayers. From 5 monolayers on, some part of the Ge appears to be fully relaxed. Uptill 12 monolayers, the growth is fully 2-dimensional and results in specular, flat surfaces; for thicker layers islanding starts (Stranski-Krastanow growth). The material is completely defect-free. According to XRD-measurements, the perpendicular strained Ge-cell dimension is 5.748 Å, which is very reproducible for all layer-thicknesses. Nevertheless, from linear elastic theory considerations, it should be 5.83 Å. The Ge-layers so formed appear to be suitable for use in short-period (SinGem)p-superlattices.

Semiconductor heterostuctures ZnxCd1−xTe/CdTe were found to be of interest recently due to their potential practical usage. The reason for this is the beautiful variety of electrical heterostucture properties which arise from the strong influence of elastic deformation distribution. Thin epilayer films and superlattices ZnxCd1−xTe/CdTe were prepared on GaAs semi-isolator substrates by MBE technology with RHEED oscillation measurements of the deposited layers. X-ray measurements have shown high crystalline quality of the samples.

We have performed Raman scattering studies of ZnxZnxCd1−xTe/CdTe structures. The data obtained were interpreted as a proff of the pseudomorphous growth model. That is, ZnxCd1−xTe/CdTe SLS keeps the lattice constant of the buffer layer.

Thin films of (AI/In)N alloys have been deposited on AIN-nucleated (00.1) sapphire by reactive (pure N2 gas) magnetron sputtering and characterized by X-ray scattering, stylus profilometry, optical spectroscopy, and electrical transport measurements. Initial efforts have concentrated on producing films with compositions near Al0.31In0.69N (bandgap tailored to GaN). The alloy sputtering targets were disks fabricated by cold pressing appropriate molar mixtures of beads of 99.99% purity Al and In. The resulting thin films are composed of heteroepitaxial grains {(00.1)InNll(00.1)sapphire; (10.0)InNll(11.0)Sapphire} and their chemical composition has been deduced from the variation in the a cell constant (as measured by the X-ray precession method) to yield equilibrium film compositions near Al0.04In0.96N and Al0.25In0.75N, respectively. Preliminary results are presented on the dependence of the quality of heteroepitaxial growth and electrical and optical properties of. these AlxIn1−xN alloy films on various growth parameters: such as chemical composition; film thickness; morphology; and substrate temperature.

By using Transmission Electron Microscopy we have studied the presence of composition inhomogeneities in In0.52Al0.48As layers grown on (100) InP. We have found a critical temperature equal to 550°C above which composition inhomogeneities start to appear nonuniformly distributed over the sample area. However, as the growth temperature increases they cover the whole layer. Furtermore, the density of stacking faults and threading dislocations increases for growth temperatures beyond the optimum value of 530°C.

GaAs/In.2Ga.8As/GaAs quantum well structures containing InGaAs layers of thickness over and under the critical thickness (hc) were studied, as grown by both conventional molecular beam epitaxy (C-MBE) and migration-enhanced epitaxy (MEE) techniques. A 6.0 monolayer per cycle (ML/cyc) growth rate, in contrast to a one or less-than-one ML/cyc growth rate used in a conventional MEE process, was used to grow In.2Ga.8As layers over hc. As-grown samples were characterized via photoluminescence, X-ray diffraction, and transmission electron microscopy (TEM). The 6.0 ML/cyc MEE-grown layers over hc show superior optical quality to MBE-grown layers with the same thickness. Both X-ray diffraction and TEM microstructure results indicate that the 6.0 ML/cyc MEE-grown In.2Ga.8As layers are still strained layers while those grown by conventional MBE method are not. The 6.0 ML/cyc MEE process seems to be advantageous for growing InGaAs layers over the critical thickness.

It has been found that y-cut LiNbO3 heteroepitaxial layers of good quality (as determined from X-ray diffraction patterns) can be obtained by radio frequency sputtering on noncrystallographic (vicinal) substrate surfaces approximating (1102) of Al2O3, in accord with the results concerning (100) Si growth on A12O3.

Such material may find application in optical modulators monolithically integrated on to silicon-on-sapphire (SOS) circuits.

The results of a transmission electron microscopy study of Co/Au and Co/Pd multilayers are reported. Special emphasis is put on the epitaxial growth and the relaxation of the misfit strain of these high misfit systems. In bright-field cross-sectional images, periodic contrast fringes are observed at the interfaces, which are the result of Moiré interference and which allow determination of the degree of misfit relaxation at the interface. It was established that 80-85% of the misfit is relaxed. From high resolution electron microscopy images the Burgers vector of the misfit dislocations was derived, being a/2<110> lying in the (111) interface plane. The results obtained for the Co/Au and Co/Pd multilayers will be discussed in comparison with those obtained for a bilayer of Co and Au.