This paper presents results of the low—temperature epitaxial growth of GaAs on Si substrates with orientation 1°—4° off (100) by molecular beam epitaxy (MBE). The epitaxial growth ·is carried out on Si wafers subjected to HF solution treatment by “spin-etch” technique before the wafer is transferred to the entry chamber of MBE system. Methods used for reducing defect density in the epitaxial layers are proposed. The characterization techniques include cross-sectional transmission electron microscopy (XTEM), plan-view transmission electron microscopy, scanning electron microscopy (S EM), and double crystal X-ray diffraction (DCXRD). Epitaxial films with a full width at half—maximum (FWHM) of about 310 arcsec measured by DCXRD are obtained without annealing.-

The initial stage of solid phase epitaxial (SPE) growth of GaAs films on the vicinal Si (001) substrate was investigated by high resolution transmission electron microscopy (H-RTEM). Cross-sectional [110] and [110] HRTEM images show that the SPE growth of crystalline GaAs islands from the amorphous phase proceeds via the formation of three-dimensional islands at the initial stage and islands' size and spacing are not critically dependent on the substrate tilt direction. The average vertical and lateral dimensions of islands were found to be 9 nm and 14 nm respectively, and the average island spacing was 10 nm. Moreover, many internal stacking faults (and/or microtwins) and a few dislocations have been already formed at this initial stage of growth. In addition, the critical thickness for misfit dislocation formation is found to depend upon the islands' lateral dimensions as well as the heights.

Molecular beam epitaxy of silicides is conventionally carried out at temperatures ≤500°C, with stoichiometric Si:metal flux ratios or deposition of pure metal. We have found novel growth modes for epitaxial CoSi2 at high temperatures coupled with Si-rich flux ratios or low deposition rates. In the first of these modes, codeposition of metal and Si at 600-800°C with excess Si leads to the formation of epitaxial silicide columns surrounded by single-crystal Si. During the initial stages of the deposition, the excess Si grows homoepitaxially in between the silicide, which forms islands, so that the lateral growth of the islands is confined. Once a template layer is established by this process, columns of silicide form as a result of selective epitaxy of silicide on silicide and Si on Si. This growth process allows nanometer control over silicide particles in three dimensions. In the second of these modes, a columnar silicide seed layer is used as a template to nucleate subsurface growth of CoSi2. With a 100 nm Si layer covering CoSi2 seeds, Co deposited at 800°C and 0.01 nm/s diffuses down to grow on the buried seeds rather than nucleating surface silicide islands. For thicker Si caps or higher deposition rates, the surface concentration of Co exceeds the critical concentration for nucleation of islands, preventing this subsurface growth mode from occurring. Using this technique, single-crystal layers of CoSi2 buried under single-crystal Si caps have been grown.

The faceted surface morphology of films grown on on-axis GaAs(111) substrates in the reconstruction regime is studied with an atomic force microscope. It reveals that facets are vicinal surfaces. Surface morphologies of films grown on substrates tilted toward different directions have been compared. An explanation is given for all observed surface morphologies. Smooth films can only be obtained on substrates tilted toward [211] in the surface reconstruction regime.

For the first time, Si1 xGex layers on amorphous SiO 2 were produced by modification of the Si surface layer of a SIMOX wafer. We used two alternative methods. An additional Si1.. Gey layer was deposited epitaxially on a SIMOX wafer followed by rapid thermal annealing. Diffusional intermixing of the layers produced a homogeneous Si1 xGex layer on SiO 2. In a second attempt, Ge was implanted into the Si surface layer and thermally treated. In both cases epitaxial Si1 xGex layers on SiO2 with minimum yield values around 9% were obtained. Rutherford backscattering and cross sectional transmission electron microscopy were used to characterize the new structures.

The potential of realizing quantum box structures via in-situ molecular beam epitaxical growth on the (111)B face of GaAs is explored. Growth is carried out on patterned (111)3B substrates with an array of truncated triangular pyramidal mesas. The mesa tops with arbitrarily small areal dimensions are used as templates for quantum box realization. Under appropriate conditions of growth along with the attendant interfacet migration, a mesa top growth profile characterized by monotonically shrinking lateral dimensions resulting in 'pinch-off is achieved.

The effect of biaxial stress on solid phase epitaxial growth (SPEG) rate of crystalline Si(100) into self-implanted amorphous surface layer has been measured. Biaxial stresses in the crystalline and amorphous phases were generated by bending the silicon wafer using the residual stresses in Ge films deposited on the back side of the wafer. Stresses were determined at SPEG temperatures by optical measurements of wafer bending curvatures. Tensile stresses up to 13 MPa in the crystalline phase and 34 MPa in the amorphous phasewere achieved during SPEG at 530ºC. An optical system based on the time-resolved reflectivity (TRR) technique was devised to measure the growth rates of two adjacent samples during a single SPEG run. This enables a direct comparison of the growth rates under different stress conditions without concern for run-to-run temperature variations. We found that the growth kinetics in all the samples were retarded as the c/a interface approached the free surface. However, the extent of this rateretardation was reducedin the stressed samples, leading to stress-enhanced growth kinetics. We speculate that the application of the biaxial tensile stresses might slow down the incorporation of hydrogen into the amorphous phase, a mechanism for the rate-retardation.

In this study, transmission electron microscopy (TEM) was used to investigate the growthconditions which produce the highest quality GaAs(111)B films by molecular beam epitaxy (MBE). Low-temperature growth using both As4 and arsine as an As2 source produced highly twinned structures, although the use of As4 provided for a smoother surface and slightly different defect structure. Two distinct twin boundaries, (112)A and (112)B, were identified by cross-sectional transmission electron microscopy (XTEM). The (112)A defect could be over-grown by a subsequent high temperature growth but the roughness associated with the (112)B defects only increased with further growth. High temperature growth of GaAs and AlAs films, while maintaining the GaAs(11)surface reconstruction, resulted in substantial reduction in the number of twins boundaries. We also found that GaAs(111)B layer quality and surface morphology can be further improved by a high temperature growth with low arsenic to Ga flux ratio of I to 1.5 ona slightly misoriented substrate.

By employing metalorganic molecular beam epitaxy (MOMBE), the heteroepitaxy of ZnSe on GaAs has been achieved using diethylselenium and diethylzinc. Significant (10x ∼ 15x) growth rate enhancement has been observed when radiation from an argon ion laser is incident to the surface; photons with energies greater than the bandgap at the growth temperature contribute to the enhancement. Photo-thermal effects are ruled out due to the low power densities used (∼200 mW/cm2). Growth rate enhancementis found to be a function of substrate temperature, VI/II gas flow ratio, laser wavelength and intensity. To further understand the effect of the laser on ZnSe growth, solid sources of Zn and Se are used in conjunction with metalorganic gas sources. The effect of laser illumination is found to depend on the combination of precursors employed: both growth rate enhancement and growth rate suppression are observed. Laser-assisted growth has application for achieving. selective area epitaxy and for tuning the surface stoichiometry.

We investigated relationships between self-texture and interfacial restriction on the epitaxy of directed, bonded, thin films. Defect structures in ZnO films grown epitaxially on (0001)sapphire mere evaluated by 3—dimensional maping of k—spacing using an X—ray double crystal spectrometer. The orientation distribution and variation in lattice spacing of the films wre individually measured to elucidate the mechanism of growth. The growth mode was found to change at a film thickness of approximately 100 Å. The layer within 100Å of the interface had a small orientation distribution (1.8'), a large lattice spacing distribution, and a large cumpressive stress.The layer that was more than 100Å from the interface had a larger orientation distribution, a smaller lattice spacing distribution, and a smaller compressive stress.

Characterization of A1GaAs layers grown in a VG-V80H chemical beam epitaxy chamber was achieved using dynamic optical reflectivity (DOR). The reflectivity for both stationary and rotating substrates was measured using a normal incidence visible laser. The DOR technique was used to measure the complex refractive index and the growth rate of the layer.The composition of the AlGaAs layer was then obtained from the published variation of refractive index with aluminum fraction. Using the refractive indices determined by DOR, good agreement with theory was achieved for the reflectivity trace from a AlGaAss/GaAs superlattice structure.

In the proposed method space and time temperature gradients are used for GaAs epitaxial deposition on Si substrates from liquid phase. Minimal Si substrate dissolution and preferential GaAs deposition from the liquid phase on Si substrate can be obtained by selecting dissolvents, requiring necessary gradients temperature values and times of active phases interaction. Because of nonuniformities in the etched Si substrate surface act as crystallization centres, the deposition process begins from GaAs island growth. Due to the dominate tangential growth rate, the separate single crystals coalesce into a GaAs monolayer.

Non-thermal Chemical Vapor Deposition (CVD) such as laser-enhanced photo-CVD of Si at low temperatures is important for Si-based heterostructures and doping superlattices. Growth kinetic models must be developed to allow these processes to be fully exploited. Intrinsic Si epitaxial layers were deposited at low substrate temperatures of 250-350ºC using the 193 nm output of an ArF excimer laser to directly dissociate Si2H6. The intrinsic film deposition rate can be described by a kinetic model that considers the gas phase reactions of the primary photolysis products and diffusion ofsilicon-bearing molecules to the growth surface. With the laser beam tangential to the substrate surface, growth rates as a function of beam-to-substrate distance have been characterized and indicate that very little gas phase reaction occurs for the dominant Si growth precursor. In order for intrinsic film deposition to result solely from Si2H6 photolysis products, a sticking coefficient ≥ 0.6 must be assigned to the dominant growth precursor in order to fit the observed yield of Si deposited in the films, indicating that the dominant growth precursor in 193 nm Si2H6 photolysis is perhaps H2SiSiH2.

We developed GaAs heteroepitaxy on a Si substrate by metalorganio vapor phase epitaxy (MOVPE) using tertiarybutylarsine (TBAs). When we preheated Si at 1000ºC in the atmosphere including TBAs, a carbide layer was formed on the Si surface. This led to polycrystalline GaAs growth. By carrying out high-temperature preheating in an H2 -only atmosphere and supplying TBAs after the preheating, we have successfully grown single-crystal GaAs with a mirror surface in a process completely free of AsH3.

Silicon lamellae grown laterally over silicon dioxide by liquid phase epitaxy are investigated using X-ray double crystal topography. The lamellae are grown from Indium solution. All of the lamellae show growth striations with indium concentration differences of about 1016...4x1017 cm−3 Overgrowth widths up to 320μm are obtained on sides of the seeding window by growth under conditions of low supersaturation. Facetting of the lamella edges then becomes less pronounced and, therefore,striations are detected farther away from the windows.

About 60% of the lamellae are free of crystallographic defects. In the defective lamellae single dislocations parallel to the sample surface are detected. They extend between seeding window edges and re—entrant corners at the lamella edges. Dislocations probably form during the cooling process due to strains near the edges of the seeding windows, and as a result of indium incorporation in high concentration.

A new method for the growth of epitaxial compound thin films, termed allotaxy, is proposed and the fabrication of the silicide heterostructure Si/CoSi2/Si(100) Is demonstrated. Allotaxy is a two. step process. In our example, Si is deposited on a heated Si substrate and then Co is coevaporated at varying rates such that a peaked Co-depth profile in Si is generated. At appropriate deposition conditions CoSi2 precipitates embedded in single crystalline Si are formed. These precipitates coarsen and coalesce into a buried, uniform, epitaxial CoSi2 layer during the second processing step, a high temperature anneal. Allotaxy should allow not only the epitaxial growth of silicides but also that of other binary, precipitates forming systems.

A rapid radiant heating, very low pressure CVD (RRH/VLP—CVD) has been successfully applied to GexSi1−x strained layer epitaxy on Si using SiH4' GeH4' B2H6 and PH3 as reaction gases at low temperature ranging from 550 to 650ĉ for operation pressure around mTorr. High quality GexSi1−x/Si strained layer heterostructure and superlattice were fabricated and high electrically active in—situ boron doping in GexSi1−x epilayer was also successfully achieved.

As demonstrated by recent STM [1] and LEED [2] experiments the platinum (110) surface undergoes, at carbon monoxide submonolayer coverages, a phase transition from the 1 x 2 “missing-row” (reconstructed) state to the 1 x 1(bulk-like) state under specific temperature and partial-pressure conditions. The catalytic oxidation reaction CO + 1/2 → CO2 drives a microfaceting instability [3] [4] of the Pt(110) surface which ends up in a regular sawtooth profile with a period ≈ 200 Å, along the [110] direction.

We introduce the idea that the rather extensive Pt mass transport, as involved in the process, could be energetically assisted by the reaction itself. Energy and momentum-balance considerations lead us to expect an energy ≲ 0.5 eV to be transferrable to thesubstrate. This should efficiently contribute to initiating the “scraping”process that leads to the microfaceted pattern.

A simple model for nucleation and growth of facets is presented (see ref. 5), yielding characteristic times of order minutes (at T = 500 K), in fair agreement with experiment.

Independently of the structural/catalytic problem, adsorption of CO at submonolayer coverages on, e.g., Pt(110) might be of interest from a surfactantphysics point of view (see ref. 6 for a very recent study on layer-by-layer homoepitaxial metal growth).

We report results of a synchrotron X-ray diffraction study of Co-Pt multilayers, with Pt[111] as the growth axis. The multilayers were grown by MBE on Pt seedfilms on basal-plane sapphire substrates at growth temperatures of 100 and 200ºC.The multilayers comprised 15 periods of Co 3Å, Pt 15Å and both exhibited perpendicular anisotropy. Grazing-incidence radial- and phi-scans revealed a set of {110{ peaks indicating doubling of real space periodicity consistent with the presence of the ordered alloy CoPt3. This supports the results of other studies which indicate interdiffused interfaces in Co-Pt multilayers and shows that chemical ordering can occur at much lower temperatures than in bulk alloys where annealing times of several days at ∼ 700ºC are required to stimulate ordering.

A new method of identifying the interfacial structure in the type-B CoSi2//Si(l11) bicrystal is presented. It involves using the kinematic structure factor equation to calculate the levels of contrast which will arise in darkfield micrographs due to steps at the interface. These are then matched to the levels of contrast measured directly from experimental images using an optical densitometer. By analysing the contrast levels measured from the same region of the bicrystal in both g=400B-aCos2 and g=111B-aCos2 micrographs, it is shown that the experimental resultsare consistent with the 7-fold coordinated interfacial structure.