Papers by Author: Patrick R. Briddon

Abstract: The influence of Ge content on the local vibrational mode of substitutional carbon in Si-rich Si1-xGex single crystals has been investigated by infrared Fourier-transform spectroscopy and ab initio modeling methods. Czochralski-grown Si1-xGex samples doped with boron and carbon have been studied. The Ge fractional content was varied from x=0.004 to x=0.044. To reveal the CS-related absorption band in the Si1-xGex the difference spectra between carbon-lean and carbon-reach Si1-xGex samples with the same Ge content were studied. We have found that the CS-related absorption band in the Si1-xGex alloys red-shifts and broadens with increasing Ge content. It has been found that at x0.015 the CS absorption band consists of two overlapping lines corresponding to different combinations of Si and Ge atoms neighboring the CS atom. The calculations show that substitutional carbon atoms avoid Ge ligand atoms, and should be found in Si-rich regions. These results also reveal that the softening of the CS mode frequency arises from the SiGe volumic expansion.

Abstract: The donor and acceptor levels of defects in Ge as well as in Si are found using a local density functional method applied to large H-terminated defective clusters. The surfaces of the clusters are modified so that their band gaps are aligned with experimental values. It is shown that the resulting energies of the first donor and acceptor levels are within about 0.2 eV of the experimental values.

Abstract: The electronic properties and structure of a complex incorporating a self-interstitial (I) and two oxygen atoms are presented by a combination of deep level transient spectroscopy (DLTS), infrared absorption spectroscopy and ab-initio modeling studies. It is argued that the IO2 complex in Si can exist in four charge states (IO− 2 , IO02 , IO+ 2 , and IO++ 2 ). The first and the second donor levels of the IO2 complex show an inverted location order in the gap, leading to a E(0/ + +) occupancy level at Ev + 0.255 eV. Activation energies for hole emission, transformation barriers between different structures, and positions of LVM lines for different configurations and charge states have been determined. These observables were calculated by density-functional calculations, which show that they are accounted for if we consider at least two charge-dependent defect structures.

Abstract: We report on a combined experimental and theoretical study of the metastable form of the vacancy-dioxygen defect in Si labeled VO∗ 2. Important new experimental observations are the detection of mixed local vibrational modes of VO∗ 2 in 16O,18O co-doped samples, the determination of the position of LVM bands for the negatively charged defect, and an assignment of an acceptor level at about Ec − 0.05 eV. Defect energetics, electrical levels and LVM frequencies of the VO∗ 2 complex are also investigated by ab-initio density-functional modeling.We find it to be a bistable defect which accounts well for the experimental data. The metastable form produces an acceptor state at 0.05 eV below Ec, and can be thought of as a VO defect perturbed by interstitial oxygen.

Abstract: We report on the energetics, electrical and optical activity of small self-interstitial (I3 and I4) clusters in Si, found from ab-initio density-functional modeling studies. I4 possesses nine local vibrational modes above the Raman edge, which account for up to three dipole-allowed vibronic transitions observed in recent experiments associated with the X-photoluminescent line. Another prominent photoluminescent line (known as the W-line) that shows a trigonal stress-induced splitting pattern, has been previously assigned to I3. Our analysis of the LVMs of a metastable form of I3 support this assignment.

Abstract: We use DFT calculations to investigate the problem of hydrogen aggregation in silicon. We study atomic structures of finite hydrogen aggregates containing four or more hydrogen atoms. Beyond four hydrogen atoms, complexes consisting of Si-H bonds are likely to form, rather than aggregates of H2 molecules, which are the most stable diatomic hydrogen complex. Our calculations show that the basic structural unit of such complexes is a hydrogenated dislocation loop, which is formed spontaneously by a structural transformation of two H∗2 complexes. Hydrogen-induced formation of dislocation loops may account for the experimental observations of dislocation loops in proton-implanted or hydrogen plasma-treated silicon. We indicate the routes leading from H∗2 aggregates and hydrogenated dislocation loops to twodimensional hydrogen-induced platelets. We discuss the effect of hydrogen-catalysed formation of dislocation loops on the plasticity of silicon.