A new technique for Ge/Si heteroepitaxy from the solution, referred to as interfacial energy epitaxy, produces Ge layers with atomically abrupt interfaces to Si and permits monolayer-controlled growth at temperatures up to 937°C. The initial driving force for epitaxy comes from interfacial energy differences between Ge, Si, and the solvent or growth mediator, whose surface free energy has to be smaller than that of Ge. A superheating of the growth solution partly out-balances this driving force, which allows us to minimize the total driving force for epitaxy. Two-dimensional growth results. Subsequent faceting and pseudomorphic island growth manifest additional driving forces for epitaxy, which may be due to interfacial- and strain energy gain.

Using hydrostatic pressure, we have transformed GaAs into an indirect band-gap semiconductor with a conduction-band minimum near the X point of the Brillouin zone. Ground to bound excited-state transitions of X-point group-IV donors in GaAs are investigated using broadband far-infrared Fourier-transform absorption spectroscopy.

We have used an optical pump-and-probe technique to measure the temperature dependence of the thermal conductivity, κ(T), of isotopically pure Si. The sample was made from 99.7% Si28 by liquid phase epitaxy. Measurements were performed over the temperature range of 100–375 K. We found an increase in the thermal conductivity of isotopically pure Si, as compared to Si of natural isotopic abundance, throughout the entire temperature range. The results were theoretically reproduced by appropriately scaling the parameters used recently to fit the thermal conductivity of Ge samples with different isotopic compositions. A maximum in κ(T) of ∼4×104 W m−1 K−1 is predicted for Si28 at T≃33 K.

Crystalline Si was grown on substrates of fused quartz, borosilicate, and sodalime glass. The glass substrates were initially coated with a seeding layer of thin nano-crystalline silicon. The nano-crystalline Si was deposited by plasma processes from a mixture of SiH4H4 gas. Then, on the seeding layer, crystalline Si was grown from a metallic solution of In or Ga solvent which was saturated with Si. The grains in the solution-grown Si reached sizes up to 100 μm. The properties of the crystalline silicon on glass are described.

We investigate by transmission electron microscopy and atomic force microscopy the development of the growth surface profile of Si 0.97 Ge 0.03 Si (001) grown from metallic solution near thermodynamic equilibrium. We show that sinusoidal surface undulations form to relax the mismatch strain elastically and result in a locally varying strain energy density at the growth surface. This leads to a locally varying difference in Gibbs free energy and thus to locally different growth rates. At sites where the strain energy is highest the layer dissolves. This dissolution in principle can be used to measure the local supersaturation of the solute at the growth surface.

Nonlinear spectroscopy of the exciton fine structure in GaAs has allowed us to measure simultaneously both magnetic dipole two-photon absorption and electric dipole one-photon absorption. The splitting of the excitonic ground state into the spin-allowed orthoexciton and the spin-forbidden paraexciton gives the electron-hole exchange energy directly. The peak assignment is proved by nonlinear magnetoabsorption. Utilizing electric dipole two-photon magnetoabsorption within the same experiment, a rich fine structure of the 2P exciton has been observed that has not been previously resolved.

By applying liquid phase epitaxy, we have grown defect-free silicon and silicon–germanium layers on partially oxide-masked Si wafers. The growth of the layers started epitaxially in oxide-free seeding areas and proceeded laterally over the thermal oxide film. Detailed studies by x-ray topography and electron microscopy show that the obtained thin semiconductor-on-insulator layers bend towards the oxide during lateral growth. The bending of the layers can be ascribed to adhesion and interfacial forces. Adhesion operates across a gap between the closely spaced surfaces of the oxide and the epitaxial Si and facilitates lateral growth of high-quality semiconductor layers on dissimilar layers or substrates. The technical potential of adhesion-dependent solution growth on dissimilar substrates is discussed.

We have grown defect-free semiconductor-on-insulator (SOI) layers by liquid phase epitaxy. Defect-free Si layers grow laterally over SiO2 by starting from seeding windows or ridge seeds on selectively oxide-masked (111) Si substrates. Growth is terminated when {111} facets at the sidewalls develop. The thin SOI layers are slightly bent in relation to the substrate and adhere firmly to the oxide film. The surface of defect-free SOI layers is formed by a perfect (111) facet, whereas monoatomic steps are found at the interfacial bottom of the layers. Although the Si layers are slightly bent, layers grown from different seeds may coalesce defect-free with seams of up to 150 μm in length. In SiGe layers on patterned Si substrates misfit and threading dislocations promote vertical growth of relaxed layers; SiGe layers grown laterally over oxide-covered Si substrates contain only few dislocations.

We prepared polycrystalline silicon layers on quartz glass and glassy carbon substrates using liquid phase epitaxy at temperatures below 920/spl deg/C. Before epitaxial growth, the substrate surfaces were coated with a 10 to 25 /spl mu/m thick silicon seed layer which we obtained by ion beam-assisted plasma deposition from a SiH/sub 4//H/sub 2/ gas mixture. The grains of these layers reached sizes up to 1 pm and had a preferential orientation in [111] direction with respect to the substrate. On the seed layer, a polycrystalline Si layer has been grown from solution. The Si crystals grew individually and had an average size of several ten /spl mu/m. Apart from twins the Si crystals were almost defect-free. Coalescences of the individual crystals with grain boundaries between them result in good lateral connections over the layer area of 4 cm/sup 2/. The results of the electrical characterization show that the layers are suitable for photovoltaic application.

Two centrifugal techniques, I and II, have been applied to grow semiconductor layers in a rotating crucible. Technique I employs centrifugal forces to transport the solutions in the liquid phase epitaxial process. Layers of Si and SiGe grown on 100 mm diameter Si wafers and of GaAs on GaAs substrates outlined the capability and potentialities of technique I. Technique II requires higher rotational frequencies of the crucible. The higher centrifugal forces available in this technique influence the local distribution of the solute in the solvent. Locally increased solute concentration in the solution allows us to prepare multicrystalline self-supporting and inclusion-free films. or to prepare thick homo- and hetero-epitaxial LPE layers even on dissimilar substrates. We describe, in this paper, experimental results obtained by growing SiGe layers on 100 mm single-crystalline Si wafers using centrifugal technique I. We describe also the first results obtained by centrifugal technique II, and thereby focus on self-supporting multicrystalline sheets of Si, SiGe, and GaAs, and on multicrystalline Ge layers grown on sintered porous quartz substrates.

High purity GaAs exhibits excited state far-infrared photoconductivity in the temperature range from 2K to 4.2K. The response is characterized by an exceptionally sharp peak which is magnetically tunable over a broad range. This dominant peak, at 35.8 cm-1 (279 μm), belongs to the 1s-2p transition of the residual shallow level impurities, and its response is over an order of magnitude above the continuum. The preliminary results of the measurements of responsivity, dark current, and NEP of this device are reported.

By means of x-ray double-crystal topography we have investigated silicon-on-insulator lamellae grown by liquid-phase epitaxy upon thermally oxidized silicon. The majority of the lamellae were free of extended defects. It is shown that the topographic contrasts of these lamellae are mainly due to vertical stress exerted by the lamellae onto the substrate. This is surprising because the aspect ratio (thickness/lateral dimension) is of the order of 10(-2). Our first calculations lead us to estimate the stress to be around 10 N cm(-2). A simple model, which may be assumed to apply in general for crystal growth on amorphous substrates, is described here. it relates the stress to an adhesive force, which acts during growth.

By liquid phase epitaxy (LPE) we have grown silicon layers on silicon and partially masked silicon at temperatures below 450 °C from Ga and Ga-In solutions. Oxidation of the cleaned silicon substrate surfaces before epitaxial growth has been prevented by a buffered hydrofluoric acid treatment. The epitaxial layers reached a thickness of 7 jim and were free of extended defects. Low growth temperatures make it possible to grow silicon layers also on pre-treated glass substrates. The amorphous glass is first coated with a thin nano-crystalline silicon layer which is deposited by plasma processes from a mixture of SiH4/H2 gas. The grains in the silicon layers grown from Ga solution on glass have reached sizes up to 100 μm.

We investigate by transmission electron microscopy and atomic force microscopy the interaction of elastic relaxation (due to roughening) and dislocation formation in Si0.97Ge0.03 grown from In solution onto Si(001). We show that formation of an undulated layer and dislocation formation are cooperating mechanisms in strain relaxation that mutually influence each other: First ripples aligned along <001> directions form, then dislocations nucleate at the rim of the substrate and cause enhanced growth at strain relaxed parts on top of these dislocations, such that ridges form. These ridges build a crosshatch pattern In the next stage of relaxation dislocations preferably nucleate near the troughs due to locally enhanced shear stresses. Based on a three dimensional finite element calculations of shear stresses in the undulated layers, we give a criterion for preferred dislocation nucleation at these troughs.

We study the interplay of elastic and plastic strain relaxation of SiGe/Si(001). We show that the formation of crosshatch patterns is the result of a strain relaxation process that essentially consists of four subsequent stages: (i) elastic strain relaxation by surface ripple formation; (ii) nucleation of dislocations at the rim of the substrate followed by dislocation glide and deposition of a misfit dislocation at the interface; (iii) a locally enhanced growth rate at the strain relaxed surface above the misfit dislocations that results in ridge formation. These ridges then form a crosshatch pattern that relax strain elastically. (iv) Preferred nucleation and multiplication of dislocations in the troughs of the crosshatch pattern due to strain concentration. The preferred formation of dislocations again results in locally enhanced growth rates in the trough and thus leads to smoothing of the growth surface.

We investigate by atomic force microscopy the early growth stages of Ge 0.85 Si 0.15 grown by solution epitaxy on Si(001). The layers grow in the Stranski-Krastanov growth mode with facetted islands of pyramidal and, with further growth, truncated pyramidal shape. Finite element calculations of the strain fields within the islands at different growth stages yield an increasing strain energy density near the island basis edges. The effect of the increase in strain energy density is to limit the lateral growth, whereas the relaxed top regions enhance growth in height.