Vibrational properties of hydrogen in compound semiconductors

Hydrogen introduced in compound semiconductors generally forms complexes with atoms of the crystal. They result from the interaction of hydrogen with some dopants, residual impurities and defects. It is shown here how vibrational spectroscopy can inform on the chemical nature of the complexes and on their structure, which can explain some electrical effects. From the experimental data, a kind of classification of the complexes, depending on the binding and location of the H atom, is established. Spectroscopy under uniaxial stress allows to determine the symmetry of the complexes and the relation with theoretical models is discussed. From the stress-induced dichroism one can derive reorientation energies related to the lattice distortion induced by the complex. An overview of the complexes in proton-implanted materials is presented and we finally try to summarize some of the questions not yet answered on the interaction between hydrogen and bulk compound semiconductors.     

Band dispersion and electronic lifetimes in crystalline organic semiconductors

The consequences of several microscopic interactions on the photoemission spectra of crystalline organic semiconductors are studied theoretically. It is argued that their relative roles can be disentangled by analyzing both their temperature and their momentum-energy dependence. Our analysis shows that the polaronic thermal band narrowing, which is the foundation of most theories of electrical transport in organic semiconductors, is inconsistent in the range of microscopic parameters appropriate for these materials. An alternative scenario is proposed to explain the experimental trends.     

Optical testability in semiconductors with density-dependent carrier lifetimes

The performance characteristics of semiconductor optical bistable Fabry-Perot devices making use of band-gap resonant nonlinearities will be significantly altered when the excess carrier recombination is density-dependent. This paper analyses the effects of radiative and Auger recombination processes in some practical etalon configurations. Optical bistability is, in general, more difficult to achieve under these conditions but suitable cavity design can significantly reduce the minimum incident intensity required.     

Vibrational properties of elemental amorphous semiconductors

Results of calculations of vibrational densities of states and of infrared and Raman spectra for relatively large model structures representing elemental amorphous semiconductors are presented and discussed. Models for four-coordinated (germanium-like), three-coordinated (arsenic-like), and two-coordinated (selenium-like) materials are included and, where possible, we compared the results with experiment and discuss the limits within which the simple models can be expected to reproduce the behaviours of real materials.     

Hypersonic modes in nanophononic semiconductors

Frequency gaps and negative group velocities of hypersonic phonon modes in periodically arranged composite semiconductors are presented. Trends and criteria for phononic gaps are discussed using a variety of atomic-level theoretical approaches. From our calculations, the possibility of achieving semiconductor-based one-dimensional phononic structures is established. We present results of the location and size of gaps, as well as negative group velocities of phonon modes in such structures. In addition to reproducing the results of recent measurements of the locations of the band gaps in the nanosized Si/Si{0.4}Ge{0.6} superlattice, we show that such a system is a true one-dimensional hypersonic phononic crystal.     

Muonium and hydrogen in semiconductors

As impurities in semiconductors muonium and hydrogen should have many similarities. In principle properties such as structures which depend primarily on their identical adiabatic potential energies should be much the same while dynamic characteristic such as diffusion would be quite different. The experimental results are in fact quite different for the two but for other reasons. This paper indicates something of the current interest in hydrogen impurities, which is mostly focussed on passivation and hydrogen pairs with other impurities or intrinsic defects, and then discusses muonium in semiconductors, where the abundant information has to do with the isolated impurity. Consequently a complete picture of hydrogen/muonium at the moment requires the study of both.     

Vibrational lifetimes and isotope effects of interstitial oxygen in silicon and germanium

Decay dynamics of local vibrational modes provides unique information about energy relaxation processes to solid-state phonon bath. In this Letter the lifetimes of the asymmetric stretch mode of interstitial 16O and 17O isotopes in Si are measured at 10 K directly by time-resolved, transient bleaching spectroscopy to be 11.5 and 4.5 ps, respectively. A calculation of the three-phonon density of states shows that the 17O mode lies in the highest phonon density resulting in the shortest lifetime. The lifetime of the 16O mode in Ge is measured to be 125 ps, i.e., approximately 10 times longer than in Si. The interaction between the local modes and the lattice vibrations is discussed according to the activity of phonon combinations.     

Structure-dependent vibrational lifetimes of hydrogen in silicon

The lifetimes of the Si-H vibrational stretch modes of the H(*)(2) ( 2062 cm(-1)) and HV.VH((110)) ( 2072.5 cm(-1)) defects in crystalline Si are measured directly by transient bleaching spectroscopy from 10 K to room temperature. The interstitial-type defect H(*)(2) has a lifetime of 4.2 ps at 10 K, whereas the lifetime of the vacancy-type complex HV.VH((110)) is 2 orders of magnitude longer, 295 ps. The temperature dependence of the lifetime of H(*)(2) is governed by TA phonons, while HV.VH((110)) is governed by LA phonons. This behavior is attributed to the distinctly different local structure of these defects and the accompanying local vibrational modes.     

Exciton dispersion law in diamond-like semiconductors

It is shown that in covalent diamond-like semiconductors the minimum of the exciton energy is situated at non-zero exciton momentum if the heavy hole mass is large enough. The depth of the minimum may be of the order of the exciton binding energy. The minimal exciton energy is calculated for several semiconductors with the variational procedure.     

Vibrational modes of the stibine molecule

In this paper, we use the algebraic approach to describe the vibrational modes of stibine molecule (of C_3v molecular symmetry group) up to 21 quanta. As the stibine molecule exhibits stretch-bend resonances, we build an algebraic pyramidal coupling operator between stretching modes and bending modes adapted to this molecule. The standard deviation associated to the fit of the vibrational levels is 1.75 cm⁻¹.     

The self-trapping of hydrogen in semiconductors

Recent theoretical calculations are discussed which show that the minimum energy site for hydrogen in silicon is the bond-centered site, while a secondary minimum is at the anti-bonding site, it is noted that these results are strongly dependent on the relaxation experienced by the silicon atoms neighboring the hydrogen. Several experimental results are discussed, namely, the observed model of the hydrogen-passivated acceptor, etching of the silicon surface by hydrogen, the exponential depth dependence of the near-surface hydrogen diffusion profile, and related muonium results, and from these results it is argued that, in some instances at least, the BC-site is the lowest energy site for hydrogen.     

States of hydrogen in crystalline semiconductors

Abstract

The stable configurations of hydrogen in undoped, and in n- and p-semiconductors are reviewed. We compare the experimentally determined configurations with theoretical predictions made by a variety of calculational methods. In undoped Si, as an example, hydrogen appears to occupy a energy occurring at a tetrahedral interstitial (T) site. In B-doped, p-type Si, hydrogen at a near BC site accounts for acceptor passivation. By contrast in n-type Si, hydrogen at the antibonding (AB) position appears to be responsible for donor passivation. The possible configurations in other semiconductors (Ge, GaAs and AlGaAs) are also summarized.     

Ultrashort excitations of surface polaritons and waveguide modes in semiconductors

Polarization-dependent structures have been formed on the silicon surface under the action of femtosecond laser pulses. Some model concepts are proposed to describe changes in the response of the semiconductor surface caused by the generation of a nonequilibrium electron-hole plasma and explain the excitation of surface polaritons and waveguide modes during a femtosecond laser pulse.     

Vibrational modes and infrared absorption of interstitial oxygen in silicon

A quasi-linear Si₂O molecule model (QLMM) is suggested from an analysis of the configuration and the interactions of an isolated oxygen atom with its neighbor silicon atoms. The vibrational modes are assigned and the infrared absorption spectra are calculated in detail with the model. The theoretical results are in reasonably good agreement with reported experimental values. This agreement shows that for the analysis of the vibrational modes of the interstitial oxygen atom in silicon crystals it is not necessary to consider the coupling of the molecule with the rest of the lattice. The interaction of the oxygen atom with its six second-nearest silicon atoms only causes the level separation of the ₂ mode and the formation of the fine structure.     

Theoretical aspects of hydrogen in crystalline semiconductors

Hydrogen in semiconductors displays behavior quite different from any other impurity, causing effects which can be either beneficial or detrimental to the electronic properties. Theoretical calculations have been able to elucidate many puzzling aspects of this behavior, by providing a microscopic picture of the interactions of hydrogen with the host lattice and with other impurities. I will critically review the available theoretical techniques, and address the following topics: microscopic structure of isolated interstitial hydrogen, as well as various hydrogen-impurity complexes; electronic structure, including the relative stability of different charge states; diffusion; and H motion around impurities.     

Vibrational modes and phase transition of Si-Ge solid solution

We present the simplified treatment where the lattice vibrations of Si or Ge atoms in the Si-Ge solid solution are replaced with that of pure Si or Ge crystal at lattice constants of the alloy. Considering the volume effect on the force constants of the pure constituent, we obtain the phonon dispersion curves of the local and band modes for Si_0.91Ge_0.09 and Si_0.11Ge_0.89 systems and the concentration x-dependence of the local and band modes frequencies in the Si_1?xGe_x solid solutions. Then, from the calculation of the effective mode Grüneisen parameter γ_i for the average phonon modes in the Si_1?xGe_x systems, we obtain the predominant correlation between TA mode Grüneisen parameter γ^X_TA at the point X and the phase transition pressure P_t, and the softening of TA modes is related to the pressure-induced phase transition of the Si-Ge solid solution.     

First-principles calculations of vibrational lifetimes and decay channels: hydrogen-related modes in Si

The vibrational lifetimes and decay channels of local vibrational modes are calculated from first principles at various temperatures. Our method can be used to predict the temperature dependence of the lifetime of any normal mode in any crystal. We focus here on the stretch modes of H2*, H+(BC), and VH x HV in Si. The frequencies are almost identical, but the lifetimes vary from 4 to 295 ps. The calculations correctly predict the lifetimes for T > 50 K and illustrate the critical importance of pseudolocal modes in the decay processes of high-frequency local vibrational modes.     

Stimulated raman scattering from plasma modes in magnetoactive semiconductors

Stimulated scattering off electron plasma mode is investigated analytically for the case when the pump wave is an intense circularly polarised electromagnetic wave propagating parallel to a homogeneous dc magnetic field in an isotropic semiconductor-plasma. The threshold electric field of the pump necessary for the stimulated Raman scattering and the growth rate of the parametrically unstable mode have been obtained for two cases (i)B ₀=0 and (ii) B₀ ≠ 0. It is seen that the magnetic field does not significantly affect the threshold electric field as well as the growth rate provided the cyclotron frequency is small compared to the frequency of the pump wave. The threshold conditions are also found to be insensitive to the electron thermal velocity.     

Vibrational modes induced by a pair of impurities

Presence of a polarizable impurity atom in an ionic crystal induces a localized vibrational mode of the lattice. The frequency of the mode is distinct from the propagating modes of the pure crystal. It is shown in this paper that the frequency of the mode depends on the polarizability of the impurity atom and on the distance of separation between two adjacent impurities.