D. J. Gravesteijn

Ge segregation at Si/Si1−xGex interfaces grown by molecular beam epitaxy

The interface quality of Si/Si1−xGex (0.08≤x≤0.33) interfaces grown by molecular beam epitaxy has been studied by means of secondary‐ion mass spectrometry. Ge segregation occurs into the Si capping layers. The segregation is characterized by a 17 nm/dec slope; the total amount of segregated Ge corresponds to a few tenths of a monolayer. The phenomenon is independent of the Ge fraction and does not depend on temperature as long as crystal growth is perfect. A possible explanation is given in terms of a Ge adlayer that is formed during growth as a result of site exchange between subsurface Ge and surface Si atoms. This adlayer is incorporated slowly during further Si growth. The Ge segregation can be suppressed by having an adlayer of Ga on the surface of the growing structure.

Microscale elastic‐strain determination by backscatter Kikuchi diffraction in the scanning electron microscope

It is shown that backscatter Kikuchi diffraction in the scanning electron microscope can be used for the determination of elastic strain with μm resolution. From the shift of Kikuchi bands in backscatter Kikuchi diffraction patterns of epitaxial Si1−xGex layers on Si(100) the perpendicular elastic strain was determined to be 2.5% for x=0.34 and at 1.0% for x=0.16 with an accuracy of about 0.1%. The values found on a μm scale were in good agreement with high‐resolution x‐ray diffraction measurements averaging over mm distances.

Materials developments for write-once and erasable phase-change optical recording

Stoichiometric amorphous films of InSb or GaSb are found to have very short (< 15 ns) crystallization times when heated to temperatures close to their melting point. They can be used for write-once amorphous to crystalline optical recording. By adding Te to InSb the crystallization time can be tuned so that erasable crystalline to amorphous optical recording is feasible with a 1-microm sized circular erase spot. Carrier-to-noise ratios of more than 50 dB are achievable at compact disk (CD) recording conditions. The erasable medium allows for CD - type run - length - !imited encoding at user bit densities of < 0.6 pm/bit.

Heterojunction bipolar transistors with SiGe base grown by molecular beam epitaxy

High-quality SiGe heterojunction bipolar transistors (HBTs) have been fabricated using material grown by molecular beam epitaxy (MBE). The height of parasitic barriers in the conduction band varied over the wafer, and the influence of these barriers on controller current, early voltage, and cutoff frequency were studied by experiments and simulations. Temperature-dependent measurements were performed to study the influence of the barriers on the effective bandgap narrowing in the base and to obtain an expression for the collector-current enhancement. From temperature-dependent measurements, the authors demonstrate that the collector-current enhancement of the HBTs can be described by a single exponential function with a temperature-independent prefactor.<<ETX>>

Characterization of low-energy (100 eV–10 keV) boron ion implantation

Low-energy boron implantations between 100 eV and 10 keV are characterized using secondary ion mass spectrometry and electrical measurements of sheet carrier concentrations and sheet resistance. Factors that may limit the use of ion implantation for future generations of semiconductor devices are discussed. At 1 keV various tilt angles show identical channeling behavior, and only a slight difference with an amorphous implant. It is found that as the energy is lowered from 1 keV to 100 eV much of the reduction in profile depth is canceled out by transient enhanced diffusion during a rapid thermal anneal. Hall–van der Pauw measurements show that with lower implant energy it becomes more difficult to activate the implanted dose. This is possibly due to increased clustering of boron, but more likely due to the fact that the surface starts to act as a trapping and deactivation center for B.Low-energy boron implantations between 100 eV and 10 keV are characterized using secondary ion mass spectrometry and electrical measurements of sheet carrier concentrations and sheet resistance. Factors that may limit the use of ion implantation for future generations of semiconductor devices are discussed. At 1 keV various tilt angles show identical channeling behavior, and only a slight difference with an amorphous implant. It is found that as the energy is lowered from 1 keV to 100 eV much of the reduction in profile depth is canceled out by transient enhanced diffusion during a rapid thermal anneal. Hall–van der Pauw measurements show that with lower implant energy it becomes more difficult to activate the implanted dose. This is possibly due to increased clustering of boron, but more likely due to the fact that the surface starts to act as a trapping and deactivation center for B.

Kinetics and mechanism of low temperature atomic oxygen-assisted oxidation of SiGe layers

The rates of low temperature atomic oxygen-assisted oxidation of strained epitaxial Si1−xGex (x=0.05, 0.1, and 0.2) layers have been measured and compared with the rate of oxidation of pure Si. We show that in the linear regime, the oxidation rate of the SiGe layer increases with the Ge concentration in the alloy. On the other hand, Ge/Si (100) structures have been oxidized. We show that this oxidation leads to the formation of pure SiO2 oxide and that the nonoxidized Ge layer is still present at the SiO2/Si interface. The oxidation rate of Si is not affected by the presence of the pure Ge interface layer. This, together with the results of SiGe oxidation, allows us to conclude that the SiGe oxidation rate is enhanced by the presence of Ge in the SiGe alloy. This can be explained by the fact that Si–Ge bonds are weaker than the Si–Si bonds. For longer oxidation times, the oxidation kinetics of SiGe layers follow a parabolic regime. We show that the parabolic constant strongly depends of the composition of...

Phase‐change optical recording in TeSeSb alloys

Some characteristics of reversible phase‐change optical data storage in TeSeSb alloys are given. High signal‐to‐noise ratios are reached at low recording energies. Upon passage of an oblong scanning laser spot, erasure occurs by growth from the crystalline surroundings of the amorphous effects at growth velocities of up to 5 cm/s. Isothermal transformation appears to be dominated by phase separation and diffusion processes. The tradeoff between long‐term stability and erasure time varies with alloy composition and, for some alloys, attractive properties with respect to data retention and erasure times are found.

Phase-change optical data storage in GaSb.

The amorphous to crystalline transition in the semiconductor GaSb has been studied as a recording mechanism for write-once optical storage. Amorphous as-deposited films, 100 nm thick, are transformed locally to the crystalline state by a focused laser beam. This recording process can be accomplished within 10 ns. The dimensions of the crystalline marks can be accurately controlled. Optical storage media based on GaSb are suitable for the archival storage of information modulated according to the compact disk format.

Germanium diffusion and strain relaxation in Si/Si1−xGex/Si structures

Abstract The thermal stability of strained Si1−xGex layers grown by molecular beam epitaxy on Si(100) was measured using Rutherford backscattering spectrometry, secondary ion mass spectroscopy and high resolution X-ray diffractometry (HRXRD). Diffusion experiments were carried out on Si1−xGex layers 50 nm thick (x = 0.07, 0.16 and 0.33) annealed at temperatures between 775 and 1010 °C for different times. The diffusion of germanium was evaluated from the broadening of the RBS and SIMS germanium profiles, while the strain relaxation was deduced from the angular shift of the (400) reflection in HRXRD. The diffusion coefficient thus measured proved to be strongly dependent on the local germanium concentration in the film. In the tails of the profile, the diffusion coefficient was comparable with the value for germanium in bulk silicon while in the centre of the film an enhanced diffusion was found. Both the initial germanium fraction x in the as-grown film and the presence of misfit dislocations hah only minor influence on the diffusion behaviour. It is concluded that safe thermal processing of these structures is possible up to 850 °C for several hours.

The interaction of Sb overlayers with Si(001)

Abstract Medium-energy ion scattering was used to study the temperature dependence of the saturation coverage, the layer morphology and reordering of the substrate after adsorption of Sb 4 tetramers and Sb 1 monomers on Si(001). Depositions at room temperature result in formation of Sb clusters on top of a dissociatively chemisorbed Sb layer. The clusters desorb at temperatures exceeding 420 K. For depositions at substrate temperatures above 570 K the Sb coverage saturates at 0.7 to 0.9 monolayer. The saturation coverage depends on substrate temperature and absorbing species, i.e., Sb 4 or dissociated Sb 4 . The highest coverages are obtained with a beam of dissociated Sb 4 . These dependencies are explained by the observation of a decreasing binding energy of the chemisorbed Sb with increasing coverage. The Si directly underneath the Sb layer is structurally bulk-like.