A. V. Drigo

On the mechanisms of strain release in molecular‐beam‐epitaxy‐grown InxGa1−xAs/GaAs single heterostructures

Inx Ga1−x As/GaAs single heterostructures have been grown by molecular‐beam epitaxy with different growing rates and In molar fractions. Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single‐ and double‐crystal x‐ray diffraction. Cathodoluminescence, x‐ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or ...

Strain relaxation in graded composition InxGa1-xAs/GaAs buffer layers

A model to compute the strain relaxation rate in InxGa1−xAs/GaAs single layers has been tested on several compositionally graded buffer layers. The existence of a critical elastic energy has been assumed as a criterion for the generation of new misfit dislocations. The surface strain accuracy results are within 2.5×10−4. The influence of different grading laws and growth conditions on residual strain, threading dislocation density, misfit dislocation confinement, and surface morphology has been studied. The probability of dislocation interaction and work hardening has been shown to strongly influence the mobility and the generation rate of the dislocations. Optimization of the growth conditions removes residual strain asymmetries and smoothes the surface roughness.

Lattice parameter in Si1-yCy epilayers: deviation from Vegard's rule

The precise C content of a series of Si1−yCy epilayer samples (0<y<0.012) was determined by resonant backscattering experiments using a 4He+ ion beam at 5.72 MeV. This beam energy is more suitable for the determination of the C content than the previously used 4.265 MeV. From the correlation of these investigations with x-ray diffraction experiments, a significant deviation of the lattice parameter variation in Si1−yCy from Vegard’s rule between Si and diamond or β-SiC was observed, which amounts up to 30% or 13%, respectively, for y<0.012. This negative deviation is in agreement with recent theoretical predictions by Kelires.

Growth and structure of titanium silicide phases formed by thin Ti films on Si crystals

The silicide formation with a titanium film deposited on 〈100〉 single‐crystal silicon, has been studied by using nuclear microanalysis, x‐ray diffraction, and transmission electron microscopy. The presence of interfacial defects and their possible role in the early stages of the reaction has been evidenced. The phase composition was dependent on the annealing temperature and time: at 550 °C only TiSi2 is observed; at higher temperatures (>600 °C), a thin TiSi2 layer at the interface is again observed, but Ti‐rich silicides grow on top of this layer by increasing the annealing time. For longer annealing times, all the reacted layer progressively transforms into TiSi2. The amount of reacted silicon grows with a (time)1/2 law; the activation energy of 1.8 eV reported for the growth of TiSi2 onto amorphous Si may be appropriate even in this case. The reaction proceeds at a rate of one order of magnitude higher than previously reported for reaction between silicon and an oxygen saturated titanium film. The kin...

Lattice disorder in implanted insulators: Pb implantation in α-Al2O3

Abstract The effects of 20, 50 and 100 keV Pb ion implantation on α-A12O3 single crystals have been investigated using the Rutherford backscattering channeling technique. Lattice disorder is observed to reach saturation at Pb doses greater than 1015 ions/cm2. Analysis of the implantation and damage profiles reveals that migration of defects occurs during implantation. It is found that the average threshold displacement energy, obtained from the measured number of displaced lattice atoms using the Kinchin-Pease equation, is dependent on implantation energy. This is discussed in terms of lattice reordering during ion bombardment which depends on the substrate temperature. The lowest value of the average displacement energy, obtained from the 20 keV samples, is 14 ± 2 eV, in reasonable agreement with the calculated Frenkel pair formation energy in α-A12O3. Lattice locations for {0110} and {1212} configurations show that the implanted Pb atoms are almost substitutional along the A1 rows. The substituti...

Sodium surface concentration analysis on glass by 23Na(p,α)20Ne nuclear reaction

Abstract The 23Na(p, α)20Ne nuclear reaction has been used to investigate the depth profile of Na near the surface of commercial soda-lime-silicate glasses. The depth profile of Na has been quantitatively determined (with a depth resolution of about 120 A) without migration effects due to the measurement method. Such perturbations, which make other analysis techniques difficult to use, appear only with very high current densities of the incident beam. A brief review of the principles of nuclear reaction used to analyse the concentration profile near the surface of samples is presented. A comparison with the traditional methods is discussed.

Atom location in complex lattices: Pb in α-Al2O3

Abstract The channeling technique has been used to locate Pb implanted into α-Al2O3 single crystal. The main purpose has been to learn how to obtain information about the location of an impurity in a complex structure. A Pb location is proposed according to data of full angular scans through different axial and planar channeling dips.

Transmission energy loss of light channeled particles in thin silicon crystals

Abstract The energy losses of light ions channeled through Si were investigated by studying the energy distribution of the transmitted particles. Beams of protons, deuterons and helium ions have been used in the energy range from 0.9 to 5.0 MeV. Measurements of the energy losses were made for the , , axial and {111}, {110} planar directions. Comparison of the energy loss for different particles shows a correlation with a simple velocity dependent function. The energy loss as a function of the incident energy is discussed in terms of localized and non localized components of the stopping power.

Radiation Damage in Spinel Single Crystals

Abstract Basic work on radiation damage behaviour in compound materials requires separate analysis of lattice defects in each sublattice. MgAl 2 O 4 spinel single crystals of 〈110〉 and 〈100〉 orientation were analysed by means of the RBS/channeling technique using 2.0–2.9 MeV 4 He beams, prior to and after implantation with Kr and Xe ions to fluences ranging from 10 14 to 10 17 at/cm 2 . The results of our study indicate that only the Al- and O-sublattices can be heavily disordered. Damage peaks for these two sublattices grow continuously with increasing the implantation fluence and eventually reach the random level for approximately 2 × 10 16 Kr(Xe)/cm 2 . The magnesium sublattice is much more stable: the height of the Mg damage peak saturates at ca. 20% of the random yield. A defect recovery stage at the temperature close to 500°C was observed.

Inhomogeneous Strain Relaxation and Defect Distribution of Znte Layers Deposited on (100)Gaas by Metalorganic Vapor-Phase Epitaxy

The structural characterization of ZnTe epilayers grown on (100)GaAs by metalorganic vapor‐phase epitaxy is reported. A detailed study of the ZnTe/GaAs heterostructure based on both high‐resolution and conventional electron microscopy and ion channeling Rutherford backscattering spectrometry allows correlation of the type and spatial distribution of the extended defects occurring at or close to the ZnTe/GaAs interface with the amount of residual lattice strain into the ZnTe epilayers. Both pure edge Lomer and 60°‐mixed misfit dislocations were identified at the interface along with partial dislocations bounding stacking faults, their overall density and distance distribution indicating the occurrence of a residual compressive strain at the heterostructure interface. By comparing this interface strain to the corresponding surface value of the same samples the occurrence of an inhomogeneous strain relaxation along the growth direction is clearly demonstrated. It is shown that such a strain gradient should b...