J. C. Barbour

Generation of misfit dislocations in semiconductors

The acting slip mechanism for the generation of misfit dislocations in diamond‐type–semiconductor heterostructures is investigated with transmission electron microscopy. It is shown that dissociation of the 60°‐mixed dislocations can lead to a difference in strain accommodation for tensile and compressive strain. A strain/thickness relation is obtained from the energy expression for nucleation of half‐loops. This relation is compared with other theoretical relations and with experimental strain data for Si/GaP(001) and In0.07Ga0.93As/GaAs(001) , measured with transmission electron microscopy and ion blocking.

Ion‐assisted pulsed laser deposition of cubic boron nitride films

Ion‐assisted pulsed laser deposition has been used to produce films containing ≳85% sp3‐bonded cubic boron nitride (c‐BN). By ablating from a target of hexagonal boron nitride (h‐BN), BN films have been deposited on heated (50–800 °C) Si(100) surfaces. The growing films are irradiated with ions from a broad beam ion source operated with Ar and N2 source gasses. Successful c‐BN synthesis has been confirmed by Fourier transform infrared (FTIR) spectroscopy, high‐resolution transmission electron microscopy (TEM), selected‐area electron diffraction, electron energy‐loss spectroscopy, and x‐ray diffraction. The films are polycrystalline and show grain sizes up to 300 A. In addition, Rutherford backscattering, elastic recoil detection, and Auger electron spectroscopies have been used to further characterize the samples. The effects of varying ion current density, substrate growth temperature, growth time, and ion energy have been investigated. It is found that stoichiometric films with a high c‐BN percentage ca...

Asymmetries in dislocation densities, surface morphology, and strain of GaInAs/GaAs single heterolayers

The dislocation densities, surface morphology, and strain of Ga1−xInxAs/GaAs epitaxial interfaces as a function of indium composition and layer thickness have been investigated by transmission electron microscopy, medium energy ion blocking, and double‐crystal x‐ray diffractometry. The electron microscopy shows that in the thinnest dislocated films (90 and 160 nm, x=0.07) 60° α dislocations form first in one 〈110〉 direction at the interface. Surprisingly, however, an asymmetry in residual layer strain is not detected in these samples, suggesting that the dislocations have the same Burgers vector or are evenly distributed between two Burgers vectors. Orthogonal arrays of dislocations are observed in films thicker than 300 nm (60° and edge‐type, x=0.07). In this case, dislocation densities in each 〈110〉 direction are equal to within experimental error while an asymmetry in in‐plane strain is measured (18% and 30% for x=0.07, 300, and 580 nm thick, respectively). An unequal distribution of Burgers vectors of...

Effects of hydrogen in the annealing environment on photoluminescence from Si nanoparticles in SiO2

The role of hydrogen in enhancing the photoluminescence (PL) yield observed from Si nanocrystals embedded in SiO{sub 2} has been studied. SiO{sub 2} thermal oxides and bulk fused silica samples have been implanted with Si and subsequently annealed in various ambients including hydrogen or deuterium forming gases (Ar+4%H{sub 2} or Ar+4%D{sub 2}) or pure Ar. Results are presented for annealing at temperatures between 200 and 1100 C. Depth and concentration profiles of H and D at various stages of processing have been measured using elastic recoil detection. Hydrogen or deuterium is observed in the bulk after annealing in forming gas but not after high temperature (1100 C) anneals in Ar. The presence of hydrogen dramatically increases the broad PL band centered in the near-infrared after annealing at 1100 C but has almost no effect on the PL spectral distribution. Hydrogen is found to selectively trap in the region where Si nanocrystals are formed, consistent with a model of H passivating surface states at the Si/SiO{sub 2} interface that leads to enhanced PL. The thermal stability of the trapped H and the PL yield observed after a high temperature anneal have been studied. The hydrogen concentration and PL yield are unchanged for subsequent anneals up to 400 C. However, above 400 C the PL decreases and a more complicated H chemistry is evident. Similar concentrations of H or D are trapped after annealing in H{sub 2} or D{sub 2} forming gas; however, no differences in the PL yield or spectral distribution are observed, indicating that the electronic transitions resulting in luminescence are not dependent on the mass of the hydrogen species.

Thermal stability of amorphous carbon films grown by pulsed laser deposition

The thermal stability in vacuum of amorphous tetrahedrally coordinated carbon (a‐tC) films grown on Si has been assessed by in situ Raman spectroscopy. Films were grown in vacuum on room‐temperature substrates using laser fluences of 12, 22, and 45 J/cm2 and in a background gas of either hydrogen or nitrogen using a laser fluence of 45 J/cm2. The films grown in vacuum at high fluence (≳20J/cm2) show little change in the a‐tC Raman spectra with temperature up to 800 °C. Above this temperature the films convert to glassy carbon (nanocrystalline graphite). Samples grown in vacuum at lower fluence or in a background gas (H2 or N2) at high fluence are not nearly as stable. For all samples, the Raman signal from the Si substrate (observed through the a‐tC film) decreases in intensity with annealing temperature indicating that the transparency of the a‐tC films is decreasing with temperature. These changes in transparency begin at much lower temperatures (∼200 °C) than the changes in the a‐tC Raman band shape an...

THE SYNTHESIS, CHARACTERIZATION, AND MECHANICAL PROPERTIES OF THICK, ULTRAHARD CUBIC BORON NITRIDE FILMS DEPOSITED BY ION-ASSISTED SPUTTERING

Significant ion irradiation is needed during growth to synthesize cubic boron nitride (cBN) films. This results in large film stresses, which have limited cBN film thicknesses to only a few hundred nm and represents a significant barrier in the development of cBN film technology. Using a new hybrid deposition technique, we have synthesized cubic BN films up to 700 nm (0.7 μm) thick. A compositional and structural analysis of the films using several standard characterization techniques confirms that relatively thick polycrystalline films with a high cBN content were synthesized. Thicker cBN films enable hardness measurements to be undertaken without major substrate effects. Nanoindentation measurements yield hardness values for the cubic BN films up to 60–70 GPa, which are greater than values measured for bulk cBN. The measured elastic modulus was observed to be lower than the bulk, and this can be accounted for by an elastic deformation of the silicon substrate. The mechanical properties of the cubic BN f...

Growth of cubic BN films on β‐SiC by ion‐assisted pulsed laser deposition

Cubic BN(c‐BN) films were deposited on cubic SiC (β‐SiC) films on Si(100) by ion‐assisted pulsed laser deposition. The films were nearly phase pure, with c‐BN fractions of up to ∼90% as determined by infrared spectroscopy. Cross‐sectional transmission electron microscopy showed that much of the film/substrate interface had a thin amorphous layer next to the β‐SiC, followed by hexagonal/turbostratic BN (h‐BN/t‐BN), and then polycrystalline c‐BN, as commonly observed on Si substrates. However, there are also c‐BN crystals that extend to within 10 A of the SiC interface, with no intervening h‐BN/t‐BN layer. A sharp falloff in c‐BN content was observed for substrate temperatures <150 °C, and below 100 °C c‐BN did not form for any ratio of the ion current flux to the deposition flux. At a different ion‐to‐substrate angle (20° closer to glancing incidence) the falloff in c‐BN content for T<150 °C was less sharp. The existence of a critical temperature for c‐BN formation does not result from a nitrogen deficienc...

Amorphous-tetrahedral diamondlike carbon layered structures resulting from film growth energetics

High-resolution transmission electron microscopy (HRTEM) shows that amorphous-tetrahedral diamondlike carbon (a-tC) films grown by pulsed-laser deposition on Si(100) consist of three-to-four layers, depending on the growth energetics. We estimate the density of each layer using both HRTEM image contrast and Rutherford backscattering spectrometry. The first carbon layer and final surface layer have relatively low density. The bulk of the film between these two layers has higher density. For films grown under the most energetic conditions, there exists a superdense a-tC layer between the interface and bulk layers. The density of all four layers, and the thickness of the surface and interfacial layers, correlate well with the energetics of the depositing carbon species.

Kinetics of NiAl3 and Ni2Al3 phase growth on lateral diffusion couples

The phase formation of NiAl3 and Ni2Al3 is studied on lateral diffusion couples of an Al‐rich source on a Ni thin film at temperatures from 375 to 500 °C. Analytical electron microscopy is used to determine the crystal structures, chemical compositions, and the widths of growing phases. Simultaneous growth of NiAl3 and Ni2Al3 is observed at 375 and 450 °C. Al atoms dominate the diffusion process in NiAl3 and Ni2Al3. The growth of Ni2Al3 has a parabolic dependence on annealing time, and the growth constant, X2/t, has an activation energy of 2.0±0.2 eV. The growth kinetics is further studied by comparing the growth rates of NiAl3 in one‐ and two‐phase growth, and by applying the criteria proposed by Gosele and Tu to the simultaneous growth of NiAl3 and Ni2Al3.

Phase formation of NiAl3 on lateral diffusion couples

The kinetics of NiAl3 phase growth is studied on lateral diffusion couples in the temperature range from 375 to 450 °C. The lateral diffusion couple consists of an Al‐rich source on a Ni2 Al3 thin film. Analytical electron microscopy is used to determine the crystal structures and chemical compositions of the growing phases. The results show that: (1) Al is the dominant moving species in the growing NiAl3 phase; (2) an equilibrium concentration of Al is established during the growth; and (3) the growth has a parabolic dependence on the annealing time. The study of NiAl3 growth kinetics on lateral diffusion couples bridges the gap between bulk and thin‐film diffusion couples in terms of reaction temperatures. The activation energy of NiAl3 growth is 1.2±0.2 eV.