R. Beserman

Initial crystallization stage of amorphous germanium films

The incubation time for the crystallization of amorphous Ge (a‐Ge) films was studied as a function of temperature between 150 and 500 °C by means of both in situ transmission electron microscopy and Raman scattering spectroscopy. The temperature dependence of the incubation time for free‐sustained a‐Ge films follows an Arrhenius curve with an overall (nucleation+growth) crystallization process activation energy of 2.0 eV. In the case where the a‐Ge films were on Si3N4 substrates, an earlier stage of the crystallization was observed (nucleation), having an activation energy of 1.3 eV. In addition, it was found that a thin metallic layer of Al or Au, deposited on the a‐Ge films, induces a very fast crystallization in the mode of dendritic growth, as reflected by a low activation energy (0.9 eV) for the incubation time temperature dependence.

Evidence of Si presence in self-assembled Ge islands deposited on a Si(001) substrate

Nominal Ge islands were grown by a molecular beam epitaxy technique on a Si(001) substrate. Island positions and shapes were measured by atomic force microscopy. Two types of islands with different sizes and shapes are present. The Si concentration distribution inside the islands was measured by Raman imaging technique with a 0.4 μm resolution, and was found to vary between 10% and 30% in large islands and be 10% in smaller islands.

Zone edge phonons in CdS1−xSex

Abstract Zone edge phonons of mixed CdS 1−x Se x have been studied by mean of infrared absorption and Raman scattering techniques. In the A point of the Brillouin zone, it has been shown that transverse acoustical phonons have a one mode behaviour, and that optical phonons have a two modes behaviour. CdS and CdSe zone center phonons can combined and give a LO(CdS) + LO(CdSe) Raman peak in addition to the 2LO(CdS) and 2LO(CdSe) peaks; this is not the case for phonons from the edge of the Brillouin-zone where no CdS + CdSe combination can take place.

Raman scattering and stress measurements in Si1−xGex layers epitaxially grown on Si(100) by ion‐beam sputter deposition

Si1−xGex thin films have been grown on silicon substrates by ion‐beam sputter deposition (IBSD). Film stress has been determined from the change in deflection curvature of the substrate after deposition and strain has been investigated by using Raman scattering spectroscopy. These properties have been studied as a function of different parameters: growth temperature, layer thickness, and annealing conditions. Raman and stress results are in close correspondence with regard to effects of deposition temperature. Si‐rich films (0≤x≤0.3) were compressively strained for all deposition temperatures. A compressive to tensile stress change was observed in the Ge‐rich alloys (x=0.6) when the growth temperature reached Tg ≊ 500 °C. In addition, the strain as a function of depth from the surface has been studied by changing the laser wavelength. The strain has been shown to increase from the surface to the interior of the film. The origin of the stress observed in IBSD films is discussed and we show that this stress...

The effect of carbon on strain relaxation and phase formation in the Ti/Si1-x-yGexCy/Si contact system

We report the first study of interfacial reactions of a metal with Si1−x−yGexCy epitaxially grown on Si. The Ti/Si1−x−yGexCy/Si (0<y<1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1−xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C‐containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations.

Structure of CdZnTe films on glass

Polycrystalline Cd1−xZnxTe films were grown on glass substrates over the full range of compositions (0 < x < 1) by metal–organic chemical vapour deposition at 480 °C. The films (~5 µm thick) showed uniform texture oriented along the 1 1 1 direction, perpendicular to the substrate, independent of the film composition. The dependence of the lattice parameter of cubic Cd1−xZnxTe on the composition followed Vegards law. The thick Cd1−xZnxTe films were shown to be of a single phase and structurally stable. The average grain size in the thick films was in the range 3–5 µm. The dominant imperfections in the films were twins (mostly Σ = 3) and dislocations. The x-ray diffraction (XRD) FWHM parameter reached a maximum at x = 0.5. Transmission electron microscopy (TEM) in situ heating in the range 200–400 °C caused plastic deformation in the grains without causing ordering effects. Optical absorption and low-temperature photoluminescence measurements confirmed the XRD and TEM results.

Heavy ion implantation in diamond

Antimony and nitrogen have been implanted at room temperature in type Ia diamonds. From the EPR spectrum we can deduce that for small implantation doses isolated broken bonds are created. Multiple defects are created for implantation doses D(Sb) = 2–5×1013 ions/cm2 and D(N) = 5×1014 ions/cm2. For higher implantation doses single broken bonds prevail. Complete graphitization is obtained for high doses: D(Sb)⩾5×1015 ions/cm2 and D(N)⩾1016 ions/cm2. In antimony doped diamonds the conductivity is only due to defects.

Kinetics of processes in the Ti–Si1−xGex systems

The kinetics of processes related to the formation of C49 and C54 Ti(Si1−yGey)2 germanosilicide phases in the two relaxed and strained Ti/Si1−xGex systems (x1=0.35 and x2=0.20) in the temperature range 600–800 °C are considered. These processes have been studied through Auger electron spectroscopy, secondary ion mass spectroscopy, x‐ray diffraction, and Raman scattering spectroscopy supported by ion beam etching techniques. Si/Ge ‘‘intergrain’’ alloy has been found between the grains of the C49 or/and C54 phases, with a Ge‐rich part Si1−zGez of z=2x–3x in the upper region. At higher temperatures, the Ge concentration in the Ge‐rich alloy decreases and its volume increases. The temperature required for obtaining similar changes are higher when x2<x1. A kinetic electron‐related model is proposed to explain the observed phenomena.

Oxidation processes in undoped GaAs and in Si‐doped GaAs

Samples of undoped GaAs‐ and Si‐doped GaAs were oxidized at different oxidation temperatures, for different durations. Three different experimental techniques that complete each other were used: Raman scattering, Auger electron spectroscopy, and the ellipsometry technique. The growth of crystalline arsenic layer takes place after oxidation during 10 h, 45 min, and 5 min at temperatures of 400, 500, and 600 °C, respectively. The oxide layer is formed as a result of three competing processes: diffusion in accordance with Fick’s law, diffusion with larger diffusion coefficient through the oxide layer, and stopping of diffusion by the crystalline arsenic layer that grows at the GaAs/oxide interface. The effect of Si doping on the oxidation process of GaAs is to impede the crystallization of the arsenic layer, to diminish the diffusion coefficient in the course of the initial stages of the reaction between the oxygen and GaAs, and to cause a small rise in the activation energy.

KINETICS OF INTERDIFFUSION IN STRAINED NANOMETER PERIOD SI/GE SUPERLATTICES STUDIED BY RAMAN SCATTERING

Intermixing time ti and interdiffusion coefficients D of nanometer periods Si/Ge strained layer superlattices (SLSs) were measured by Raman scattering technique. Si12Ge12 and Si19Ge9 SLSs have been annealed in the temperature range 760–900 °C during various time intervals. The observed D and ti follow the Arrhenius‐like behavior with different activation energies ΔE=1.78±0.15 eV and 3.94±0.15 eV and pre‐exponential factors D=2×10−10 cm2 s−1 and 0.7 cm2 s−1, respectively, for the Si12Ge12 and Si19Ge9 SLSs. D, ti, ΔE, and D0 are strongly affected by the changes of the SLS layer thickness, and strain. An explanation of the experimental observations is proposed in terms of the kinetic electron‐related theory of atomic diffusion in solids. The observed variations of ΔE and D0 are related to the material parameters, which are characterized by picosecond atomic and electronic phenomena in nanometer regions, in good agreement with the observations.