摘要:

A simple method is presented for calculating the stress and strain distributions arising from an initially uniformly strained quantum dot of arbitrary shape buried in an infinite isotropic medium. The method involves the evaluation of a surface integral over the boundary of the quantum dot and is therefore considerably more straightforward to implement than alternative stress evaluation techniques. The technique is ideally suited to calculating strain distributions within disordered arrays of pyramidal quantum dots prepared by Stranski–Krastanow growth. The strain distribution for a cuboidal quantum dot is presented and compared to that of a rectangular quantum wire. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365210

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Stress in crystalline TiN/amorphous B–C–N multilayered thin films has been determined by the substrate curvature technique. It is established that the total stress is dependent on the number of deposited bilayers and on the bilayer repeat length. The linear relationship between the stress and the inverse of the bilayer repeat length allows calculation of the value of the interface stress. It is found to be compressive with a value between 1.79 and2.46 J/m2,depending on the calculation method. An apparent dependence between the interface stress and the total thickness of the multilayer film is observed. It is interpreted as an additional relaxation due to an increase of the roughness of the interfaces when the number of deposited bilayers is increased. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365211

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Among the growth approaches being considered currently to realize quantum dots and quantum wires is the selective epitaxial growth on patterned substrates. With this technique the feature size and geometry are mainly limited by the lithographic process. With optical lithography we achieved a lateral dimension of⩾0.4&mgr;m. Therefore, to further reduce the lateral dimension, but still using optical lithography, the tendency toward facet formation during selective epitaxial growth was investigated. Si0.70Ge0.30multiple quantum well structures with Si0.935Ge0.065spacers and buffers were deposited on (001) Si. The buffer thickness was varied so as to achieve facet junction. While on large areas the Si0.935Ge0.065buffer was relaxed, for dots⩽300&mgr;m or narrower the structures remained strained even for buffer thicknesses exceeding by a factor of two–three the critical thickness of large area. In dots and wires where facet junctioning has taken place a rounded region between facets (approximately 50 nm broad) in the quantum well layers was observed. In wires oriented parallel to⟨100⟩sidewalls self-organized wire formation and vertical correlation of these growth induced wires was observed. The photoluminescence of all dots and wires down to the lowest achieved dimension and including the self-organized wires is strong, with the integral intensity normalized to the surface coverage for 100 nm dots exceeding by a factor of 50 the emission from unpatterned areas. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365212

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this study, we examined the microstructure of Ag films grown on Si(001) substrates by radio frequency (rf) magnetron sputtering in a synchrotron x-ray scattering experiment. At a low rf power of0.22 W/cm2,the film was initially nucleated in the form of fine-grained epitaxial film with the crystalline axes parallel to the substrate crystalline axes. As the growth proceeded further, it changed to nonepitaxial three dimensional island growth. The Ag islands were not epitaxial, but grew preferentially along the ⟨111⟩ direction. At a higher rf power of0.44 W/cm2,the Ag film developed a nonepitaxial island growth from the early stage. Annealing the films at 500 °C increased the island size and enhanced the crystalline quality. The thin epitaxial film grown at the low rf power was recrystallized into islands during the annealing. This study suggests that it is feasible to grow heteroepitaxial Ag films on silicon substrates even by a sputtering process when the energy of the sputtered particles is minimized. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365213

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A model of one dimensional grain growth in a bicrystal film, driven by surface anisotropy, is presented. The equation of surface diffusion (Mullins Equation) and the curvature driven boundary equation of motion are simultaneously solved under a set of matching and boundary conditions that includes the mechanical equilibrium at the discontinuous points (surface corners due to anisotropy and grain boundary groove roots), the conservation of surface flux and the continuity of chemical potential at the groove root. An analytical solution is obtained for the steady state motion. This solution is investigated as a function of the degree of anisotropy. It is found that a steady state motion is possible for a limited range of anisotropies. Below a critical degree of anisotropy the film breaks up. It is shown that the steady state velocity decreases with the degree of anisotropy. Numerical analysis of the time dependent problem demonstrates that the steady state solution is stable. It is shown that anisotropy stabilizes the process of grain growth against film breakup. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365214

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical, optical, and structural properties of nitrogen-doped hydrogenated amorphous silicon films with the N content up to about 12 at. &percent; are systematically studied using electrical conductivity measurements, electron-spin resonance, light-induced electron-spin resonance, constant photocurrent method, optical absorption spectrophotometry, IR absorption spectroscopy, Raman scattering spectroscopy, and x-ray photoelectron spectroscopy. Both behaviors of the dark conductivity and the charged-dangling-bond density against the N content suggest that most of charged dangling bonds originate from potential fluctuations. Only part of charged dangling bonds created by the N doping up to 2 at. &percent; originate from positively charged fourfold-coordinated N. The decay behavior of the photoconductivity after turning off the probing light also supports that most of charged dangling bonds in N-doped hydrogenated amorphous silicon do not originate from positively charged fourfold-coordinated N. A possible origin of potential fluctuations is increased fluctuations in the net electron density at Si sites accompanying structural randomness caused by the N doping. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365215

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The interaction of aCl2plasma with a Si(100) surface has been investigated by angle resolved x-ray photoelectron spectroscopy (XPS). It was found that the amount of chlorine incorporated into the near-surface region of Si increases with ion energy, and does not change with long exposure to the plasma. Chlorine is present asSiClx(x=1–3)with average relative coverages (integrated over depth) of[SiCl]:[SiCl2]:[SiCl3]≅1:0.33:0.13at−240 Vdc bias (mean ion energy≈280 eV) and 1:0.34:0.087 at 0 V dc bias (mean ion energy≈40 eV), at x-ray photoelectron spectroscopy (XPS) binding energies of 100.2, 101.2 and 102.3 eV, respectively. Moreover, there is a substantial amount of disordered Si within the chlorinated layer at high ion energy, reflected in a broadening of the 99.4 eV Si peak and the appearance of a shoulder at 98.8 eV, ascribed to Si with a dangling bond. In addition, bulk Si plasmon losses associated with theCl(2p)andCl(2s)core levels indicate that roughly one-third of the Cl in the near-surface region is surrounded by bulklike Si at the high ion energy. Modeling of the dependence of the relative concentration of Cl on the take-off angle was used to estimate the Cl content and thickness of the surface layer. From an inversion of the observed take-off angle dependence of the relative Cl and Si XPS signals, depth profiles were derived for the near-surface region. Cl content falls off in a graded fashion, over a depth of about 25 and 13 Å for a mean ion energies of 280 and 40 eV, respectively. The Cl areal density (coverage integrated throughout the layer) increases with increasing mean ion energy from1.8×1015 Cl/cm2at 40 eV to3.5×1015 Cl/cm2at 280 eV. From a similar inversion of the take-off angle dependence of theSiClxsignals,SiCl2andSiCl3are found to be largely confined at the top∼5 Å,while below the surface, disordered Si and SiCl are present. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365216

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The surface topography and structure of low-pressure chemical vapor deposited silicon films on thermal oxide grown on (100) silicon substrates have been investigated after different processing steps. Atomic force microscopy topographic measurements are performed on undoped as-grown samples and afterex situphosphorous doping from aPOCl3source. In addition, topographies of the doped films are obtained using constant current scanning tunneling microscopy on hydrofluoric acid passivated surfaces under high vacuum. As a result we have found that surface topography and roughness are mainly determined by the deposition process. Roughness of films deposited at 620 °C is related to the grain structure represented by hillocks with typical lateral dimensions between 50 and 150 nm in the images. Doping by high temperature diffusion and subsequent annealing causes a complete recrystallisation of the film, leading to typical lateral grain sizes between 200 and 600 nm. However, the surface topography of the doped films still remains determined by the hillocks formed by the deposition process. Values of the surface roughness are between 7 and 14 nm depending on the process step. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365232

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Niobium films were deposited by physical vapor deposition (PVD) and ion-beam-assisted deposition (IBAD) using ion energies of 0, 250, 500 and 1000 eV, andRratios (ion-to-atom arrival rate ratio) of 0, 0.1, and 0.4 on (100) silicon, amorphous glass, and (0001) sapphire substrates of thickness 50–1000 nm. Besides a {110} fiber texture, an in-plane texture was created by orienting the ion beam with respect to the substrate. The in-plane texture as measured by the degree of orientation was strongly dependent on both ion-beam energy and theRratio. In fact, the degree of orientation in the films followed a linear relationship with the energy per deposited atom,En.The grain structure was columnar and the column width increased with normalized energy. The surface morphology depended on both the normalized energy of the ion beam and the film thickness. All films had domelike surface features that were oriented along the ion-beam incident direction. The dimension of these features increased with normalized energy and film thickness. Surface roughness also increased with normalized energy and film thickness, with the root-mean-square roughness increasing from 1.6 nm for the PVD sample (100 nm thick) to 36.7 nm for the IBAD film (1000 eV,R=0.4,800 nm thick). Both the surface morphology evolution and in-plane texture development in these films were the result of the different ion sputter rates among differently oriented grains. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365217

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By employing a deep level transient spectroscopy (DLTS) technique, this work investigates the deep trap levels of rf-sputtered(Ba0.4Sr0.6)TiO3(BST) thin films deposited at various temperatures. Arrhenius plots of DLTS spectra detect a single trap located at 0.45 eV in 450 °C deposited films, whereas two traps located at 0.2 and 0.40 eV appear in 550 °C deposited films. On the other hand, examining theI–Vcharacteristics of the films at the temperature range of 298–403 K reveals the presence of two conduction regions in the BST film capacitors, having ohmic behavior at low voltage(<1 V)and Schottky-emission or Poole–Frenkel mechanism at high voltage(>6 V).The barrier height and trapped level are, respectively, estimated to be 0.46 and 0.51 eV, corresponding to the trap activation energy 0.4–0.45 eV obtained from our DLTS measurements. Compared with previous published reports, the trap distributed at 0.4–0.5 eV should be an intrinsic defect of BST and possibly ascribed to be oxygen vacancies. Meanwhile, the trap plays a prominent role in the leakage current of BST films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365218

出版商:AIP    

年代:1997

数据来源: AIP