Room-temperature epitaxial growth of CeO2(001) films on YSZ buffered Si(001) substrates

2 (001) epitaxial thin films deposited on Si(001) with yttria-stabilized zirconia buffers have been obtained for the first time at room temperature by pulsed-laser deposition. The influence of oxygen pressure on the crystal quality of CeO₂ was studied for the films deposited at 100 °C. The rocking curve full width at half maximum of the CeO₂(002) peak for films deposited at room temperature and 100 °C was between 1° and 2°, for oxygen pressures below 3×10^-2 mbar. The best crystal quality was obtained at around 3×10^-3 mbar. Epitaxial growth at room temperature was confirmed by cross-sectional transmission electron microscopy. Scanning electron microscopy and atomic force microscopy revealed very smooth surfaces for oxygen pressure below 3×10^-2 mbar, with rms roughness values around 0.3 nm over 5 μm×5 μm. Received: 25 September 1997/Accepted: 22 April 1998     

Comparative study of epitaxial growth of Pt and Ir electrode films grown on MgO-buffered Si(100) by PLD

(200)-oriented Pt and Ir electrode films have been epitaxially grown on MgO/Si(100) by in situ pulsed-laser deposition (PLD). A comparison of crystallinity and surface morphology of both electrode films was made. It was found that both electrode films featured remarkable atomic-scale smooth surfaces and had the same epitaxial relationship with substrates. Different from the noncompact surface morphology of the Pt film, the morphology of the Ir film offers a rectangular grain shape and the grains are arrayed regularly and compactly. The difference in the surface morphology of both electrode films is briefly explained in terms of the degree of species saturation. PACS 81.15.Fg; 68.55.Jk; 61.14.Hg; 68.55.-a; 81.15.-z; 77.55.+f     

Electron-stimulated desorption of thin epitaxial films of KBr grown on (100)InSb

We have measured time-of-flight (TOF) distributions of Br atoms desorbed from thin (less than 1000 Å) epitaxial films of KBr on (100) InSb with a 2 keV electron beam. Although the general structure of the TOF spectra was similar to that obtained previously for the thick crystals, both the fast and the slow (thermal) components of the distribution were strongly dependent on the film thickness. We argue that this dependence is due to two different diffusion processes involved in the transport of the primary excitation products from the bulk to the surface. By measuring the velocity resolved ESD yield for films of various thicknesses, we determined that a diffusion length of the carriers responsible for the thermal ESD component varied from 30 to 700 Å with temperature in the range 20–300°C. In contrast, for the non-thermal desorption we found the carrier diffusion length of about 140 Å which did not depend significantly on the temperature.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)     

Room-temperature photoluminescence of doped 4H-SiC film grown on AlN/Si(100)

Well-defined room-temperature photoluminescence (PL) was observed from 4H-SiC films on AlN/Si(100) complex substrates grown at temperatures below 1150 °C by the chemical vapor deposition method. The PL spectrum consists of three major emission peaks in the vicinities of 3.03, 3.17 and 3.37 eV. By the combination of experimental measurements and theoretical analysis, the origins of the PL emission peaks have been identified and associated with N donors, Al acceptors in the 4H-SiC films and the band-to-band transition between the second minimum of the conduction band and the top of valance band of the 4H-SiC. The room-temperature SiC PL can be much utilized for optoelectronic high-power, high-frequency and high-temperature applications in the ultraviolet spectral regime. PACS 81.05.Hd; 81.05.Ea; 78.55.-m     

Plastic relaxation anisotropy in epitaxial films grown on miscut Si(001) substrates

A way of calculating the structural parameters of semiconductor epitaxial layers grown on miscut (0 0 1) substrates is developed. It is shown that the difference between the tensor of film elastic strains and the spherical tensor of strains translating the film’s crystal lattice into the substrate’s lattice is a tensor whose components are proportional to X-ray strains. The technique is used to analyze GaAs and Ge_0.2Si_0.8 films grown on (1 1 13) Si substrates. The anisotropy of the degree of plastic relaxation is established for lateral directions perpendicular and parallel to the interfacial steps in the GeSi film. It is proposed that noninteger Miller indices be used to denote the direction and value of the rotation of the film’s crystal lattice with respect to the substrate lattice.     

Ion-beam-induced ferromagnetism in Ca-doped LaMnO3 thin films grown on Si (100)

The ion-bean-induced room temperature ferromagnetic ordering in pulsed laser deposited Ca-doped LaMnO₃ thin films grown on Si (100) are presented in the present study. In addition to this, changes bought by the ion beam in structural, morphological and electrical properties are presented. Dense electronic excitation produced by high energy 120?MeV Ag⁹⁺ ion irradiation causes change in surface roughness, crystallinity and strain. It is also evident that these excitations induce the magnetic ordering in this system. The observed modifications are due to the large electronic energy deposited by swift heavy ion irradiation. The appearance of ferromagnetism at 300?K in these samples after irradiation may be attributed to the canting of the antiferromagnetically ordered spins due to the structural distortion. It is observed that the irradiated films show higher resistance than unirradiated films for all the compositions.     

Photoacoustic spectroscopy of thin SiO2 films grown on (100) crystalline Si substrates

Photoacoustic Spectroscopy (PAS) has been used to measure the thickness of thin SiO₂ films grown on (100) Si wafers. The data are in reasonable agreement with a simple theoretical model. It suggests that photoacoustic Spectroscopy is complementary to optical interferometry, in that it is capable of giving quantitative estimates of thin transparent films on opaque substrates of low reflectivity via the transmitted fraction of the optical energy incident on the sample. Both theoretical and experimental results indicate that PAS can be very useful in the measurement of thin films on substrates of low reflectivity.     

In situ RHEED analysis of epitaxial Gd2O3 thin films grown on Si (001)

Epitaxial Gd₂O₃ thin films were successfully grown on Si (001) substrates using a two-step approach by laser molecular-beam epitaxy. At the first step, a ～0.8 nm thin layer was deposited at the temperature of 200 ^°C as the buffer layer. Then the substrate temperature was increased to 650 ^°C and in situ annealing for 5 min, and a second Gd₂O₃ layer with a desired thickness was deposited. The whole growth process is monitored by in situ reflection high-energy electron diffraction (RHEED). In situ RHEED analysis of the growing film has revealed that the first Gd₂O₃ layer deposition and in situ annealing are the critical processes for the epitaxial growth of Gd₂O₃ film. The Gd₂O₃ film has a monoclinic phase characterized by X-ray diffraction. The high-resolution transmission electron microscopy image showed all the Gd₂O₃ layers have a little bending because of the stress. In addition, a 5–6 nm amorphous interfacial layer between the Gd₂O₃ film and Si substrate is due to the in situ high temperature annealing for a long time. The successful Gd₂O₃/Si epitaxial growth predicted a possibility to develop the new functional microelectronics devices.     

Oxidation kinetics of epitaxial Ge-covered Si(100) surfaces

We compared oxidation kinetics on Ge-covered Si(100) surfaces grown at 350 and 600°C for 0.9 and 2.0 ML Ge overlayer thicknesses. The O_KLL intensities showed clear oxidation enhancement on the surfaces grown at 600°C. The oxygen interaction for the surface covered with 2 ML Ge formed at 350°C was weaker than for the Ge(100) surface, indicating that the compressive strain due to the lattice mismatch may suppress the oxygen interaction with surface Ge dimers.     

Strain-driven morphology of Si1-xGex islands grown on Si(100)

A study has been carried out on the morphology and structure of three-dimensional (3D) SiGe islands grown by molecular beam epitaxy (MBE) on Si(100) substrates. Samples of Si1-xGex alloys have been prepared to investigate the effects either of the alloy composition or of the growth temperature. Atomic force microscopy (AFM) evidenced the growth of 3D islands and transmission electron microscopy (TEM) demonstrated wetting layer growth on Si(100), independently on the deposition conditions. Energy dispersive spectroscopy (EDS) micro-analyses carried out on cross-sections of large Si1-xGex islands with defects allowed a measurement of the Ge distribution in the islands. To the best of our knowledge, these have been the first experimental evidences of a composition change inside SiGe islands. The interpretation of the experimental results has been done in terms of strain-enhanced diffusion mechanisms both of the growing species (Si and Ge) and of small islands.     

Studies of interface structures of W films grown on patterned and bare Si(100) by TEM

+ Si(100) and bare Si(100) wafers by low pressure chemical vapour deposition (LPCVD) at 230–280 °C. The films were investigated by transmission electron microscopy (TEM). The cross-sectional TEM samples of W/Si(100) exhibited a fine scale interface roughness, which was attributed to the surface preparation. Irregular W plug structures were observed depending on the predeposition procedures. It was observed that an insufficient deposition of W films on the contact surface leads to the presence of aluminium around and underneath the plugs. This was observed by energy dispersive X-ray spectrometry (EDX). A study, using conventional electron diffraction, confirmed that no silicides formed at the interfaces of W-bare Si(l00) wafers. Received: 16 December 1996/Accepted: 6 May 1997     

Study of the wurtzite zinc-blende mixed-structured GaAs nanocrystals grown on Si (111) substrates

The structure and growth mechanism of GaAs nanocrystals grown on Si (111) substrates by using the molecular beam epitaxy method have been studied using transmission electron microscopy. The isolated nanocrystals had hexangular shapes, with aspect ratio ～1 and high symmetry. The crystal structure of the GaAs nanocrystals contains a mixture of a stable state of zinc-blende and a metastable state of wurtzite. A number of thin wurtzite layers parallel to the Si (111) plane are introduced into the zinc-blende GaAs nanocrystals as stacking faults. Formation of partial dislocations near the GaAs/Si interface and the small difference in the Gibbs free energy between the zinc-blende and wurtzite structures could cause formation of wurtzite as stacking faults in the zinc-blende structure