Raman study of phonons and intraband electronic excitations in antimony

Abstract

Line shapes of the zone-center optic modes Eg and A&g in Sb have been measured at 80 K by Raman scattering. The results indicate asymmetry in the wings. The E~m ode, in particular, shows a Fano line shape which is believed to arise from the interaction between the phonon and intraband electronic Raman scattering within the penetration depth of the metal. Although the cross section for the latter process is usually small for normal metals, in antimony, because of the anisotropic multivalleyed Fermi surface and small effective mass of the carriers, it is likely to be significant.The manifestation of interaction between overlapping discrete-continuum states as Fano interference in the phonon line shape in solids has been observed experimentally by Raman scattering. For insulating crystals like BaTiO3and AlPO~, the continuum is provided by phonon bands' (one or two phonons), whereas in heavily doped semiconductors like p-type Si, ' and 315 superconductors like V3Si, ' vertical interband transitions between occupied and unoccupied states give rise to a continuum of electronic energy levels overlapping the phonon frequency.In semimetals like Bi and Sb the free carriers are generally located at Brillouin-zone edges in pockets with small effective mass at the Fermi level. ' Sb with a carrier density of -10 cm provides an interesting example in which light light scattering processes can give rise to intraband intervalley transitions spanning an energy range of qc vF -250 cm, where qc is related to the inverse penetration depth of light in the medium and vF is average electron velocity at the Fermi level. In this paper we report Raman studies in Sb. Careful measurements show asymmetric line profiles for the zone-center optic phonons which we attribute to Fano-type interaction between one-phonon scattering and intraband electronic Raman scattering. Antimony has a rhombohedral crystal structure (D3$) with two atoms per unit cell. The zone-center optic phonons are Raman active but infrared inactive and can be classified into one nondegenerate mode A l and a doubly degenerate mode Eg. The corresponding Raman tensors have the following form' (hexagonal axis system is chosen here;trigonal axis is taken as the z axis):(2) (f 15 cm) lenses. An incidence angle 8 of approximately 30' was used for convenience, since for 8~30' the specularly reflected beam clears the collection lens. The light scattered in the [001] direction (with a spread of about 24' cone) was collected by a F/1 lens system and focused on the entrance slit of a homemade grating double monochromator. A polaroid was placed in the scattered beam to select diagonal (A~, + Eg ) and off-diagonal (Eg ) components of the Raman scattering tensor. Low-temperature measurements were performed using a homemade liquidnitrogen cryostat. The signal was detected using a cooled FW-130 multiplier phototube. The data were recorded in the digital mode with a spectral band pass of 2.8 cm '. Our values of phonon frequency and width are in general agreement with the earlier measurements. ...

Effect of pressure on the Raman modes of antimony

“…15 These asymmetries are weak, however. So, for the purpose of extracting peak positions and approximate line width parameters from the Raman data for the A7 phase, a fitting by symmetric pseudo-Voigt line shapes was found to be adequate.…”

“…31,32,33 A coupling between the optical phonon modes and lowenergy electronic excitations appears to be supported by a Raman study. 15 Now, the pseudogap of Sb is expected to change significantly (towards filling up) under pressure, leading to a major change in the coupling of phonons to electronic states near the Fermi level. 9 Furthermore, the response in the visible spectral range may be affected also, in particular the so-called E 2 transition near 2.5 eV 34 which at ambient pressure is in resonance with the exciting laser energy used in this study.…”

“…15 The coherent A 1g phonon generation in Sb by short laser pulses is the subject of several more recent reports. 16 Raman experiments on Sb under pressure were performed FIG.…”

MBE growth and characterization of dilute InNSb film

“…While the band at 145cm -1 attributed to the A lg Sb element mode was not obvious. It could be believed that there are fewer Sb defects in our samples compare with that of Ref [7]. The FWHM of LO mode at 300K is only about 5 cm -1 , also indicating high quality of the InNSb film.…”

Cluster Assembled Sb Films: Studies On Structure, Surface And Optical Properties

“…The Raman shifts observed at 112.8 cm À1 and 153 cm À1 , respectively, can be identified as the A 1g and E g vibrational modes, following Zitter and Watson (1974), who earlier had reported their observation at 115 cm À1 and 150 cm À1 corresponding to the E g and A 1g modes, for bulk Sb. However (Bansal and Roy, 1986) had reported the observation of only the A 1g mode around 150 cm À1 again for bulk antimony. It should be noted from 8 that both observed modes for the Sb cluster deposited film are shifted by 2 to 3 cm À1 from their bulk values.…”