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Phonons broadening parameters

By evaluation of the phonon-mode frequencies, information about strain [29] or about the incorporation of doping or alloying atoms can be derived. Besides the phonon-mode frequency, the phonon-mode broadening parameter provides information about crystal quality [30], because scattering due to a lower crystal quality or due to alloying makes the phonon-mode broadening parameter larger. [Pg.80]

Typical phonon mode broadening parameters for a set of ZnO thin films grown on silicon by PLD with varying oxygen partial pressure and/or substrate heater power are shown in Fig. 3.14. Heitsch et al. [30] observed that the... [Pg.100]

Fig. 3.14. Phonon mode broadening parameters, as determined by IRSE, vs. oxygen partial pressure for a set of PLD-grown ZnO thin films on (111) silicon. Triangles and squares represent data of thin films grown with substrate heater power of P = 400 W and P = 600 W, respectively. Reprinted with permission from [30]... Fig. 3.14. Phonon mode broadening parameters, as determined by IRSE, vs. oxygen partial pressure for a set of PLD-grown ZnO thin films on (111) silicon. Triangles and squares represent data of thin films grown with substrate heater power of P = 400 W and P = 600 W, respectively. Reprinted with permission from [30]...
Fig. 3.15. Phonon mode broadening parameters of PLD-grown rocksalt-structure MgzZni-zO thin films on sapphire. Reprinted with permission from [74]... Fig. 3.15. Phonon mode broadening parameters of PLD-grown rocksalt-structure MgzZni-zO thin films on sapphire. Reprinted with permission from [74]...
In addition to defects and impurity incorporation, alloy-induced disorder further increases the phonon mode broadening parameters, as discussed... [Pg.101]

Table VI. Experimental and theoretical values of the intensities for the TO-phonon assisted indirect transitions in silicon. The relative and actual (in parentheses in units of cm ) experimental values were obtained by multiplying da/dE by the broadening parameter F. The theoretical values were calculated using... [Pg.472]

Further, the presence of anisotropic distortion of the basal plane of a-plane wurtzite layers, [s 7 Sy ), will lift-off the degeneracy of the x and e Sy. Therefore, the IR dielectric functions Sx and Sy provide access to the frequencies and broadening parameters of the TO and LO phonons with Ei symmetry polarized along the x = [1120] and y = [1100] directions. In other words, the splitting of the TO and LO with Ei symmetry that is predicted theoretically by Equation 9 [14,16] can be obtained from the IR eUipsometry data analysis. Note, that polar c-plane GaN heteroepitaxial layers that experience anisotropic distortion of the basal plane, for instance when grown on a-plane sapphire [29] will also allow assessment of the Ei phonon splitting [17, 18]. In this case, the optical measurement will depend on the orientation of the plane of incidence and incident polarization with respect to the two in-plane directions X = [1120] and y = [1100]. The standard eUipsometry measurement for non-c-plane-oriented and anisotropically strained wurtzite crystals is inapplicable and the generalized eUipsometry approach is needed. [Pg.234]

The frequencies and the broadening parameters of the Fi phonons polarized in the jc-y plane parallel to the GaN [1120] and [1100] directions, extracted from... [Pg.242]

Table 9.4 Best-fit values and standard deviations of the , (TO), (LO), and phonon frequencies, to, and broadening parameters, y, for polarizations along the GaN [1120] (/ = x) and [1100] / = y) directions for an o-plane GaN film. Forthe ] modes, j denotes the phonon polarization, while for the 2 modes, j denotes the polarization of the incident light in the parallel and cross-polarized configurations, respectively. Table 9.4 Best-fit values and standard deviations of the , (TO), (LO), and phonon frequencies, to, and broadening parameters, y, for polarizations along the GaN [1120] (/ = x) and [1100] / = y) directions for an o-plane GaN film. Forthe ] modes, j denotes the phonon polarization, while for the 2 modes, j denotes the polarization of the incident light in the parallel and cross-polarized configurations, respectively.
While there are no experimental data available for cubic ZnO at atmospheric pressure, ab initio calculations for phonon properties of cubic ZnO, which relied on experimental data of rocksalt ZnO studied under high pressures ( 8 GPa) as input parameters, have been undertaken [55]. The predictions by such an exercise for a>ro and cOlo lead to 235 cm and 528 cm, respectively, for cubic ZnO. The values are smaller than those obtained by extrapolating the IRSE analysis. However, it should be pointed out that both extrapolations follow the same trend in predicting phonon mode frequencies and that they are smaller than those of hexagonal ZnO. The width of phonon modes depends on sample quality and processes that lead to broadening. A discussion of phonon mode broadening parameters can be found in Ref. [26, 27]. [Pg.358]

In this chapter some of the presently known optical properties of zinc oxide are reviewed. In particular, the anisotropic dielectric functions (DFs) of ZnO and related compounds from the far-infrared (FIR) to the vacuum-ultraviolet (VUV) spectral range are studied. Thereupon, many fundamental physical parameters can be derived, such as the optical phonon-mode frequencies and their broadening values, the free-charge-carrier parameters, the static and high-frequency dielectric constants, the dispersion of the indices of refraction within the band-gap region, the fundamental and above-band-gap band-to-band transition energies and their excitonic contributions. [Pg.79]

Figs. 2.9,2.10, recorded at very low temperatures and in high resolution. For a crystal of very high quality, the broadening of these transitions is mainly due to phone- >. We briefly analyze their influence on the reflectivity in order to assure that no spurious structures are considered. These spectra have been recorded for the first time and analyzed by Turlet et al.1-67. We simply summarize a few points necessary to test the KK transformation, to point out the specificity of the intrinsic relaxation mechanisms related to exciton-phonon couplings, and to evaluate quantitatively the corresponding coupling parameters. [Pg.83]

Figure 3.13. Temperature evolution of the parameter re T) of the first-surface exciton (hollow circles). The full circles indicate the values obtained for the bulk exciton (Fig. 2.14). The quasi-coincidence at T 0 is fortuitous, but the surface states appear less broadened than the bulk states in the region 30-50 K, which could correspond to a decay at the surface of the density of interplane phonons coupled to the exciton (see Section III.B). Figure 3.13. Temperature evolution of the parameter re T) of the first-surface exciton (hollow circles). The full circles indicate the values obtained for the bulk exciton (Fig. 2.14). The quasi-coincidence at T 0 is fortuitous, but the surface states appear less broadened than the bulk states in the region 30-50 K, which could correspond to a decay at the surface of the density of interplane phonons coupled to the exciton (see Section III.B).
Whenever the external vibrations produee large anisotropic displacement parameter values for the scattering atoms it will exaggerate the impact of any given value of Q. The phonon wing envelope will move to even higher frequencies and the response will broaden. Only two characteristics of a sample bear on its anisotropic displacement parameter (with samples at low temperatures), the effective molecular mass, Hef[, and the Einstein frequency, see ( 2.6.2.1). The lighter the... [Pg.60]

Substitution of the cation in the solid solution system Smi R Se by, e.g., Y or La reduces the lattice parameter and the 4f-5d excitation gap, without yielding the transition into the metallic intermediate-valence phase (Gronau 1979). In fig. 3 we show the polarized Raman spectra of Smj jjY Se at 80K for x = 0, 0.25, 0.50, 0.75 and 1.0, obtained by Giintherodt et al. (1981a). For the sake of completeness, Sm, jLag jSe has also been included. For the latter sample one observes below 200 cm first-order defect-induced Raman scattering from acoustic and optical phonons which is absent in pure SmSe. The / = 1 peak of Smo gjLap osSe has drastically broadened compared to that of pure SmSe at... [Pg.167]


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See also in sourсe #XX -- [ Pg.80 , Pg.100 , Pg.101 ]




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