Coupled plasmon–LO-phonon modes inGa1−xMnxAs

Abstract

The vibrational and electronic properties of Ga 1Ϫx Mn x As layers with Mn fractions 0рxр2.8%, grown on GaAs͑001͒ substrates by low-temperature molecular-beam epitaxy, are investigated by micro-Raman spectroscopy and far-infrared ͑FIR͒ reflectance spectroscopy. The Raman and FIR spectra are strongly affected by the formation of a coupled mode of the longitudinal optical phonon and the hole plasmon. The spectral line shapes are modeled using a dielectric function where intraband and interband transitions of free holes are included. In addition to the coupled mode, the contributions of a surface depletion layer as well as a symmetry forbidden TO phonon have to be taken into account for the Raman spectra. Values for the hole densities are estimated from a full line-shape analysis of the measured spectra. Annealing at temperatures between 250 and 500°C results in a decrease of the hole density with increasing annealing temperature and total annealing time. Simultaneously, a reduction of the fraction of Mn atoms on Ga lattice sites is deduced from high-resolution x-ray diffraction.

Theory of ferromagnetic (III,Mn)V semiconductors

“…II.B and V.B.2 we mentioned x-ray spectroscopies ͑core-level photoemission and XMCD͒ used to characterize Mn 3d states and detect the sign and magnitude of the p -d exchange coupling. Dispersions of hole bands in DMSs have been studied by angle-resolved photoemission with ultraviolet excitation ͑Okabayashi et al, 2001͑Okabayashi et al, , 2002Asklund et al, 2002͒ and infrared-to-ultraviolet Limmer et al, 2002;Seong et al, 2002͒. Spectroscopic studies of isolated Mn͑d 5 + hole͒ impurities in the infrared region provided key information on the valence of Mn in ͑Ga,Mn͒As, as discussed in Sec.…”

Raman scattering study on Ga1–xMnx As prepared by Mn ions implantation, deposition and post‐annealing

“…Phonon mode at 277 cm -1 In a polar semiconductor, an LO phonon and the plasmon formed by the free carriers interact via their macroscopic electric fields [3]. The compositional dependence of GaAs-like LO phonon and CLOPM was investigated in Ga 1-x Mn x As crystals grown by MBE [2], where CLOPM was found to superimpose with LO GaAs mode.…”

“…There is, however, still not much known about the details of electronic and vibrational properties of this material. Up to now, few Raman scattering studies have been carried out in the Ga 1−x Mn x As materials grown by MBE [2,3], in which only GaAs-like phonon modes and coupled-LO-phonon plasmon mode (CLOPM) are observed. Although some Raman scattering studies have been made in ion-implanted GaN [4,5], Raman scattering studies have not been carried out in the Ga 1−x Mn x As prepared by the Mn ions implantation, deposition, and post-annealing, which is more useful in fabricating various devices.…”

Electronic- and band-structure evolution in low-doped (Ga,Mn)As

“…Quantitative analysis of that type of Raman spectra can provide important information on the free-carrier density in heavily doped semiconductors. A reliable method of determining hole concentration in (Ga,Mn)As layers, based on analysis of their Raman spectra, without applying large magnetic fields, which is required in the Hall-effect measurements for ferromagnetic materials in order to extract the ordinary Hall effect from the dominating anomalous Hall effect, was proposed by Seong et al 28 By examination of the relative Raman intensities of the LO-phonon and CPLP lines and their shift toward the TO-phonon position, and comparing them with the literature data, 27,28 we have estimated the hole concentrations of 0.5×10 19 …”