A higher‐order extended finite element method for dislocation energetics in strained layers and epitaxial islands

This paper presents a higher‐order method for modeling dislocations with the extended finite element method (XFEM). This method is applicable to complex geometries, interfaces with lattice mismatch strains, and both anisotropic and spatially non‐uniform material properties. A numerical procedure for computing the J‐integral around a dislocation core to determine the energy release rate for a virtual advance of the dislocation line is described. Several examples in three dimensions illustrate the applicability of this method to material interfaces and semiconductor heterostructures, specifically the computation of the energetics of systems of dislocations in SiGe islands deposited on pure Si substrates. Copyright © 2010 John Wiley & Sons, Ltd.     

Spontaneous formation of vertical magnetic-metal-nanorod arrays during plasma-enhanced atomic layer deposition

A novel fabrication method of Co and Ni metal nanorods (NRs) without catalyst or template, based on the spontaneous formation of NRs during plasma-enhanced atomic layer deposition (PE-ALD) is developed. Pure Co and Ni NRs 9-10 nm in diameter are synthesized on SiO(2) and Si substrates by using metal-organic precursors and an NH(3) plasma mixed with a suitable amount of SiH(4) as a reactant. The lengths of the NRs are controlled on the nanometer scale by changing the number of PE-ALD growth cycles. Superconducting quantum interference device magnetometer measurements confirm the magnetic anisotropy of Co NRs caused by shape anisotropy.     

Defect formation in epitaxial layers of cadmium mercury telluride solid solutions highly doped with indium

We have studied the effect of strong (up to 5×10²¹ cm^?3) indium doping on the behavior of components in cadmium mercury telluride solid solutions. At an indium concentration in a modified subsurface layer on the order of 10²¹ cm^?3, these layers are depleted of mercury and cadmium; simultaneously, cadmium is segregated in the region immediately below the indium-doped surface layer. The strong doping with indium leads to the formation of extended defects, which is manifested by characteristic patterns in electron micrographs observed after chemical etching. The observed redistribution of the solid solution components upon doping is explained by peculiarities of the defect formation in cadmium mercury tellurides.     

Rotatable magnetic anisotropy in epitaxial ferrite layers

Magnetic domain structure and magnetic anisotropy were studied in monocrystalline epilayers of Mg0.9Mn0.3Fe1.8O4ferrite. The layers, several micrometers thick, were obtained by a CVD method on monocrystalline MgO substrates. Domain observations were performed by the Bitter's method. Magnetic anisotropy measurements were performed by torque and FMR methods. In the demagnetized state, a typical stripe structure of 2.0 to 2.8 μm period was observed. From the domains behavior in the in-plane magnetic fields it was found that in these epilayers the rotatable anisotropy was present. The existence of this anisotropy was confirmed by torque measurements in small in-plane fields. The magnetic parameters characterizing these layers are: 4ΠM = 3500 Gs, K1= - 2.2 × 10⁴ergs/cc, KN= 2.3 × 10⁵ergs/cc.     

Photothermal deflection studies of GaAs epitaxial layers

Photothermal beam deflection studies were carried out with GaAs epitaxial double layers grown on semi-insulating GaAs substrates. The impurity densities in thin epitaxial layers were found to influence the effective thermal diffusivity of the entire structure.     

High-temperature diode formed by epitaxial GaP layers

The preparation of pure, undoped, high-temperature GaP grown by liquid-phase epitaxy is reported. Results are presented of studies of GaP p-n structures grown at various crystallization initiation temperatures, using the capacitance-voltage (C-V) method and deep-level transient spectroscopy (DLTS). The characteristics of GaP are determined by the low concentration of background impurities and deep-level defects. Measurements of the temperature dependence of the forward branch of the current-voltage characteristic showed that the thermometric characteristic of the diode is linear between −191 and ∼+600 °C. Pis’ma Zh. Tekh. Fiz. 24, 1–7 (May 12, 1998)     

Double-cross epitaxial overgrowth of nonpolar gallium nitride layers

Epitaxial gallium nitride (GaN) structures have been manufactured by the lateral overgrowth technology, whereby GaN epilayers are grown in stripe windows on a partly masked initial GaN layer. It is established that in addition to the traditional orientation of stripes across the c axis, the process is also possible for the stripes oriented at 45° relative to this axis. In this case, two lateral overgrowth processes in mutually perpendicular directions can be performed, which would significantly reduce the relative area of imperfect material formed over windows in the mask.     

Carrier recombination at dislocations in epitaxial gallium phosphide layers

The nature of dark spots observed in cathodoluminescence micrographs of gallium phosphide epitaxial layers has been examined using the transmission electron microscope and etching studies. Each dark spot is shown to be located at the intersection of a dislocation with the layer surface. Moreover screw, edge and mixed dislocations all give rise to spots of similar size and intensity. It is suggested that enhanced non-radiative recombination which gives rise to the dark spots is due to the core structure, rather than a concentration of dopant atoms, method of layer growth, etc., and that different core structures are equally effective.     

High boron incorporation in selective epitaxial growth of SiGe layers

Incorporation of high amount of boron in the range of 1 × 10²⁰–1 × 10²¹ cm⁻³ in selective epitaxial growth (SEG) of Si_{1 − x}Ge_x (x = 0.15–0.315) layers for recessed or elevated source/drain junctions in CMOS has been studied. The effect of high boron doping on growth rate, Ge content and appearance of defect in the epi-layers was investigated. In this study, integration issues were oriented towards having high layer quality whereas still high amount of boron is implemented and the selectivity of the epitaxy is preserved.     

Behavior of epitaxial GaAs layers as α particle detectors

The properties of epitaxial GaAs-based p ⁺-n structures used as light-ion (α particle) were studied. A comparison is made with the latest published data on the possibilities of present-day semi-insulating GaAs (SI-GaAs). It is noted that the content of impurities and structural defects forming deep levels in the band gap of the material is two orders of magnitude lower in epitaxial layers. The deep levels determine the conditions of transport of nonequilibrium carriers in the detector, allowing for trapping of the carriers, and they also determine the electric-field profile. The charge-carrier lifetime was found to be ≥ 200 ns. This is two orders of magnitude longer than the values for SI-GaAs, in complete agreement with the lower content of deep centers. It is shown how deep centers influence the field profile, forming a quite large region of low field values. Pis’ma Zh. Tekh. Fiz. 24, 8–15 (April 12, 1998)     

Nanofabrication of self-organized, three-dimensional epitaxial oxide nanorods

In this article, we address the nanofabrication process of self-organized, three-dimensional (3D) epitaxial oxide nanorods of perovskite La_1−xSr_xMnO₃ and fluorite Gd₂Zr₂O₇ using pulsed laser ablation. These nanorods are epitaxially grown on (001) LaAlO₃ substrate and are well defined with a very narrow size distribution as studied by transmission electron microcopy. All of the nanorods are encapsulated by uniformly thick amorphous-like boundaries. The nanofabrication process leading to formation of 3D nanorods in these systems is discussed by considering the interplay of misfit strain energy and surface energy contributions.     

Investigations of selectively grown GaN/InGaN epitaxial layers

We have studied GaN/InGaN heterostructures grown by selective area low pressure metalorganic vapor phase epitaxy (LP-MOVPE). A GaN layer already grown on the c-face of sapphire has been used as substrate, partly masked by SiO₂. In a second epitaxial step a GaN/InGaN single heterostructure and GaN/InGaN/GaN double heterostructures were grown on the unmasked rectangular fields. We obtained good selectivity for GaN and for InGaN. A larger growth rate as compared to planar epitaxy and strong growth enhancement at the edges was observed. Spatially resolved measurements of the luminescence show an increase in indium incorporation of about 80% at the edges. Besides the larger indium offering at the edges, this is due to an enhanced growth rate. Very smooth facets are obtained. The influence of pressure on the surface morphology and growth enhancement was investigated.     

Microstructure and properties of epitaxial layers by laser glazing

Various processes of laser surface melting are employed to modify the features of epitaxially grown microstructures in the melt. Three kinds of microstructures are demonstrated in this investigation. The one with complex microstructures possesses the best resistivity against hot stress corrosion.     

Deep-level studies in GaN layers grown by epitaxial lateral overgrowth

The electrical properties, deep-level spectra, microcathodoluminescence (MCL) spectra and diffusion lengths of minority charge carriers were measured in GaN films grown by the epitaxial lateral overgrowth (ELOG) technique. The results are compared to the properties of GaN layers grown in a standard fashion without masking of the initial template. MCL and electron beam induced current (EBIC) imaging of the laterally overgrown regions revealed the presence of dark spots with density of 1-5 × 10⁶ cm^− 2 that are associated with individual dislocations. The concentration of deep electron and hole traps was found to be much higher in the standard material than in the ELOG material. Diffusion lengths of minority carriers determined from EBIC signal profiling gave values of 0.8-1 μm along the bright regions and 0.4-0.5 μm in the dark regions of the ELOG samples. Similar measurements on metal organic chemical vapor deposition templates gave a diffusion length of 0.4-0.5 μm, close to the diffusion length in the dark stripes of the ELOG samples.