The presence of configuration interaction, between the "internal" acceptor states of group III impurities in silicon and P₃⁄₂ band Bloch states, has been observed. The effect of impurity-impurity interaction on the line shape of the boron, gallium and indium internal acceptor lines has been studied. The observed characteristic asymmetric line shape is explained by introducing the interaction of the internal state with the degenerate P₃⁄₂ valence band Bloch states, and the inhomogeneous impurity-impurity interaction. The ionization energy of the substitutional impurity in the host lattice is found to be a deciding factor in this interaction. The internal and external absorption spectra of silicon doubly-doped with boron and indium acceptors is studied. The observed broadening of the boron external absorption lines in Si(B,In) is explained by neutral impurity scattering. The presence of indium in Si(B,In) crystal lattice, modifies the P₃⁄₂ valence band Bloch states and hence the configuration interaction. This modification is found responsible for the observed features of the boron 2p′ internal line in Si(B,In). The coupling between the lattice and the impurity bound carrier for deep monovalent acceptors in silicon, such as gallium and indium, is found to be stronger than for the shallow boron impurity. This suggests the possible existence of phonon-assisted transitions associated with these deep impurities. Such transitions are observed in the absorption spectrum of indium doped silicon. The phonon-assisted transitions are superimposed on the photoionization continuum transitions of the indium acceptors. Interference effects between the phonon-assisted transition and the transitions to the continuum states modify the position and line shape of the transitions. Using the phonon dispersion curves for silicon, interpretation of the results is presented. As a supplementary study, the temperature dependence of the indium external line 2, is investigated. The temperature dependence of halfwidth of indium line 2 in Si(In) supports the stronger electron-phonon coupling in Si(In). / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The introduction of boron into a silicon crystal lattice produces two sets of acceptor impurity states: (i) the "external" states (which include the acceptor ground state) which are associated with the P₃/₂ valence band maxima and are the usual impurity states lying in the forbidden gap, (ii) the "internal" states which are associated with the P₁/₂ valence band maximum and are degenerate with P₃/₂ continuum states. The energies of the transitions from the ground state to the so-called 2p', 3p' and 4p' internal acceptor states are such that the 2p', 3p' and 4p' internal absorption peaks are seen in the infrared. Three different experiments are performed to study the "internal" spectrum of boron-doped silicon. (i) The stress-perturbed behavior of the 2p' and 3p' absorption peaks is studied with the use of calibrated uniaxial stress (≤ 10⁹ dynes/cm² ) and polarized light. From these data it is deduced that the ground state has a ⌈8 symmetry while the 2p' and 3p' internal states each have a ⌈6 symmetry. In addition the deformation potential parameters of the ground state are calculated to be: b' = -0.66 ± 0.04 eV. and d' = -2.1 ± 0.2 eV. These calculated parameters for the ground state are used to obtain indirectly some information about the deformation potential parameters of the P₃/₂ valence band edge. (ii) For the temperature range 5°K ≤ T ≤ 60°K the temperature dependences of the breadths of the 2p' and 3p' peaks are measured. These temperature dependences are attributed to phonon broadening. The phonon broadening mechanism for the 2p' and 3p' peaks is shown to be primarily due to a lifetime effect caused by electron-phonon coupling of the 2p' and 3p' states to the P₃/₂ valence band states. (iii) For the impurity concentration range 2.6 x 10¹⁵ boron/cm³ ≤ N ≤ 4.5 x 10¹⁷ boron/cm³ the 2p' absorption peak is measured. With increasing concentration this peak is observed to broaden and become very asymmetrical. Explanations to the above data are presented. / Science, Faculty of / Physics and Astronomy, Department of / Graduate