Electron uniaxial stress

Fig. 18. Raman spectra of the B—H complex under [100] uniaxial stress. [ Reprinted with permission from The Materials Research Society, Stutzmann, M. and Herrero, C.P. (1988). Defects in Electronic Materials, MRS Proceedings 104 (eds. M. Stavola, S.J. Pearton and G. Davies), p. 271. Also from Stutzmann and Herrero, 1988. And with permission from the American Physical Society, Herrero, C.P. and Stutzmann, M. (1988). Phys. Rev. B 38, 12668.]... 

Figure 12. Electrical conductivity as a function of relative electron (donor) concentration in P doped Si to illustrate the metal-nonmetal transition at 0 K. The relative P density is varied by changing nc with uniaxial stress on a single sample. The open circles are extrapolated to T = 0 K (from Thomas33).

In crystals, impurities can take simple configurations. But depending on their concentration, diffusion coefficient, or chemical properties and also on the presence of different kind of impurities or of lattice defects, more complex situations can be found. Apart from indirect information like electrical measurements or X-ray diffraction, methods such as optical spectroscopy under uniaxial stress, electron spin resonance, channelling, positron annihilation or Extended X-ray Absorption Fine Structure (EXAFS) can provide more detailed results on the location and atomic structure of impurities and defects in crystals. Here, we describe the simplest atomic structures more complicated structures are discussed in other chapters. To explain the locations of the impurities and defects whose optical properties are discussed in this book, an account of the most common crystal structures mentioned is given in Appendix B. 

The exact structure of TDDs in silicon and the origin of the double donor behaviour has been a matter of controversy for many years. The ESR measurement indicates that these centres are oriented in the crystal along the <110> axes. ENDOR measurements have also shown that they involved O atoms. The consensus is that they are complexes whose atomic constituents are O and Si atoms, and that their atomic structure is dominated by Si-O-Si zigzag chains along the <110> direction. This will be discussed in Chap. 8, where the results of electronic absorption measurements under uniaxial stress are presented. 

A detailed presentation of the piezospectroscopy of semiconductors can be found in [124]. Uniaxial stress is the most easily-produced perturbation (for experimental details, see Sect. 4.7.1), and the spectroscopy performed under stress is called piezospectroscopy. The relevant piezospectroscopic parameters for an impurity line are the number of components observed, their polarization characteristics and the amplitude of their shifts and splitting as a function of the value of the stress. Piezospectroscopy is useful when studying degenerate electronic transitions of the EM-like centres as it can lift intrinsic degeneracy. It can also lift the orientational degeneracy of electronic (and vibrational)... 

In this section, we first consider the effect of mechanical stresses on EM electronic transitions and present typical examples. The second part develops the relation between orientational degeneracy and splitting under uniaxial stress or other external perturbations. 

We consider first the effect of a uniaxial stress on the EM-like electronic spectra of donors with CB degeneracy and then the situation for acceptors. 

Up to now, the centres considered in this chapter were isolated atoms with cubic symmetry, but it has been seen in Chap. 6 that there exists many other donor centres with non-cubic symmetry. These centres, with symmetries lower than cubic, present an orientational degeneracy in addition to the electronic degeneracies related to their atomic structure. The effect of a uniaxial stress on their spectroscopic properties depends also on this additional degeneracy so that it cannot be treated as a whole. The general piezospectroscopic properties of non-cubic centres in cubic crystals have been discussed by Kaplyanskii [73]. 

The DLTS measurement of the uniaxial-stress dependence of the electron emission rates of the S° and S 1 ground states have allowed determination of the shear DP associated with these centres, and values in the 10.7-11.6eV range have been obtained for temperatures between 150 and 220 K [99]. 

In some sense this is similar to a uniaxial stress applied to the bulk crystal. For the semiconducting SmS (100) surface such surface relaxation, if large enough, is expected to have drastic influence on the electronic structure of the Sm ions, because the semiconductor-metal transition occurs when the bulk lattice constant has been... 

The spin Hamiltonian of the Er + and Dy ions in the LiRp4 crystals is given by formula (118) with the Zeeman term in the form of eq. (119) and with The constants of spin-phonon interaction, calculated with the parameters of electron-deformation interaction from table 10, are given in table 25 (some of these constants were measured in EPR experiments on the uniaxially stressed LiTmF4 crystals activated by the Er and Dy + ions). In this case parameters of the magnetostriction Bx T, h) in eq. (235) can be written as follows... 

Field dependence of electron drift velocity Cyclotron resonance with uniaxial stress... 

Heyd, R., Charlier, A., 8c McRae, E. (1997). Uniaxial-stress effects on the electronic properties of carbon nanotubes. Physical Review B, 55(11), 6820-6824. 

Spatially resolved STS has been used to characterize the electronic structure of Cgg molecules on a range of substrates including Au(OOl), Au(llO), Au(lll) and Al(lll). Due to a lattice mismatch between the overlayer Cgg and the substrate Au(lOO) surface, a uniaxial stress is applied resulting in several types of oblique lattices and modified electron charge density around the Cgg molecules. Charge transfer from the substrate to the molecules and intermolecular bonding under stress were observed in STS data. STS also clearly differentiates inequivalent adsorption sites on Au(lll) and Al(lll). The STM tip has been used to locally excite single Cgg molecules to luminesce with an emission spot size of 0.4 nm. Fullerenes have been... 

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