J. Bak-Misiuk

Lattice dilation by free electrons in heavily doped GaAs:Si

Lattice constants of GaAs layers grown by molecular beam epitaxy were examined by using the high resolution x‐ray diffractometer. For highly doped samples (up to 9×1018 cm−3 of free‐electron concentration) we observed an increase of the lattice constant with respect to the undoped layers. Since substitutional silicon atoms decrease the lattice constant of GaAs, the results are explained by the influence of free‐electrons via the deformation potential of the Γ minimum of the conduction band. The best fit to our diffractometric data was obtained for the band‐gap deformation potential equal to −8.5 eV.

STRAIN IN GAAS LAYERS GROWN BY LIQUID PHASE EPITAXIAL LATERAL OVERGROWTH

High resolution x-ray diffraction has been used to study strain in GaAs layers grown on GaAs substrates by the liquid phase epitaxial lateral overgrowth (ELO) technique. We show that the lattice and thermal expansion coefficient mismatch between the subsequent layers and the substrate, as well as the built-in strain in the SiO2 masking film, lead to long-range deformations (macroscopic bending) extending over the whole area of the sample. Moreover, we show evidences that microscopic bending of individual ELO stripes takes place due to adhesion of their laterally overgrown parts to the masking film.

Microscopic bending of GaAs layers grown by epitaxial lateral overgrowth

X-ray diffraction has been used to study the influence of the mask material on properties of GaAs layers grown by the liquid phase epitaxial lateral overgrowth (ELO) on (100) GaAs substrates. We show that ELO stripes bend towards the SiO2 mask in the direction perpendicular to seeding lines in a similar way to that as studied recently by x-ray topography for Si lamellae [H. Raidt, R. Kohler, F. Banhart, B. Jenichen, A. Gutjahr, M. Konuma, I. Silier, and E. Bauser, J. Appl. Phys. 80, 4101 (1996)]. The bending disappears when the mask is removed by selective etching. This microscopic bending is reduced by nearly 2 orders of magnitude when graphite instead of SiO2 is used to mask the substrate.

Lattice parameters of GaN single crystals, homoepitaxial layers and heteroepitaxial layers on sapphire

Lattice parameters of gallium nitride were measured using diffraction of X-rays produced by the laboratory generators and the European Synchrotron Radiation Facility (ESRF). The following samples were examined: (i) bulk single crystals grown at high hydrostatic pressure, undoped and Mg-doped, (ii) homoepitaxial layers grown on those crystals, undoped, Mg-doped and Si-doped, (iii) heteroepitaxial layers grown on sapphire, (iv) heteroepitaxial layers on sapphire after high-pressure annealing treatment, (v) heteroepitaxial layers on sapphire after implantation and thermal processes. The lattice parameters were measured versus free-electron concentration established by photoluminescence, far-infrared reflectivity and the Hall method. It is concluded that the main factor causing an increase of the lattice parameters of GaN are free electrons which act via the deformation potential of the conduction band. For heteroepitaxial layers, the strains caused by the mismatched substrates are discussed in terms of the mosaicity of these layers and thermal mismatch with respect to the substrates.

Asymptotic x-ray scattering from highly mismatched epitaxial films

We study x-ray diffraction peak profiles from highly mismatched relaxed epitaxial films at momentum transfers exceeding the peak widths. Calculated profiles for misfit dislocations are compared with triple-crystal diffraction profiles from GaAs/Si(001) epitaxial films. We find that the longitudinal and transverse scans have a common q−4 asymptote but approach it differently, so that their profiles are qualitatively different in the experimentally available momentum range. The possible contribution from threading dislocations is estimated.

X-ray diffraction peaks at glancing incidence and glancing exit from highly mismatched epitaxial layers

We find that the widths of double-crystal x-ray diffraction peaks in asymmetric reflections of relaxed GaAs∕Si(001) heteroepitaxial layers in reciprocal diffraction geometries (glancing incidence and glancing exit) are notably different. This observation is in agreement with previous measurements on other heteroepitaxial systems but apparently contradicts the reciprocity principle of electrodynamics. We show that the apparent contradiction originates from the summation of the scattered waves that are collected by the detector in a double-crystal setup and resolve it by giving an appropriate description of the peak widths.

Effect of external stress on creation of buried SiO2 layer in silicon implanted with oxygen

Abstract The effect of external stress exerted by enhanced (up to 1.5 GPa) hydrostatic pressure (HP) of argon ambient during annealing of oxygen-implanted silicon (oxygen dose ≤1×10 17 cm −2 ) up to 1470 K on oxygen agglomeration has been investigated by secondary ion mass spectrometry, transmission electron microscopy, and X-ray and photoluminescence methods. HP treatment results in oxygen distribution shift and massive creation of oxygen precipitates, whereas creation of dislocations is strongly suppressed.

Study of the conversion of the VO to the VO2 defect in silicon heat-treated under uniform stress conditions

The VO defect is one of the major defects produced by irradiation in Cz-grown Si. Its presence in the infrared spectra is manifested by a localized vibration mode (LVM) band at 829 cm−1. Upon annealing, the decay of this band is accompanied by the emergence in the spectra of another LVM band at 890 cm−1 generally attributed to the VO2 defect. The annealing of the VO center is discussed in the literature by considering mainly two reaction processes in neutron irradiated material, that is, VO+SiI→Oi and VO+Oi→VO2, which could occur in parallel. There are some points, however, which cannot be explained within the above reaction scheme. In this article we report infrared, x-ray, transmission electron microscopy and selective etching investigations on the annealing behavior of the VO defect, in neutron-irradiated Cz-grown Si samples, subjected to various high temperature–high pressure (HTHP) treatments prior to the irradiation. The contribution of each of the above two reactions to the whole annealing process ...

Structure of Oxygen - Implanted Silicon Single Crystals Treated at ≥1400 K under High Argon Pressure

The structure of oxygen - implanted (up to a dose 6x10 17 cm -2 ) silicon, Si:O, treated at 1400 - 1550 K under high (up to 1.5 GPa) argon pressure, was investigated by numerous methods. The oxygen distribution peak narrowed, the dimensions of extended defects decreased and the peak intensity in the Si - O - Si asymmetric stretching vibrational mode diminished with pressure. That effects are explained by decreased misfit at the SiO 2-x /Si boundary and more numerous nucleation sites created in Si:O treated at high pressure.

Stress - Dependent Out - Annealing of Defects in Self - Implanted Silicon

Effect of hydrostatic pressure (HP) on out – annealing of defects in self – implanted silicon (Si:Si, Si+ doses 5x1016 cm-2 and 1x1017 cm-2, energies 50 keV and 160 keV), treated for 1 – 10 h at up to 1400 K (HT) under HP ≤ 1.4 GPa, has been investigated by photoluminescence, X-ray and related methods. Applied at 720 – 1270 K enhanced pressure does not affect or affects adversely Si:Si structure while at 1400 K assists in its improvement. HP – dependent transformations in Si:Si at HT are related to effect of HP on diffusion of point defects, such as silicon interstitials and vacancies produced at implantation. Out - annealing of defects in self - implanted silicon is dependent also on spatial position of damaged areas in Si substrate.