Andrii Nikolenko

Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes

Micro-Raman spectra of single-walled carbon nanotubes in the range of two-phonon 2D bands are investigated in detail. The fine structure of two-phonon 2D bands in the low-temperature Raman spectra of the mixture and individual single-walled carbon nanotubes is considered as the reflection of structure of their π-electron zones. The dispersion behavior of 2D band fine structure components in the resonant Raman spectra of single-walled carbon nanotube mixture is studied depending on the energy of excitating photons. The role of incoming and outgoing electron-phonon resonances in the formation of 2D band fine structure in Raman spectra of single-walled carbon nanotubes is analyzed. The similarity of dispersion behavior of 2D phonon bands in single-walled carbon nanotubes, one-layer graphene, and bulk graphite is discussed.

Infrared Reflectance Analysis of Epitaxial n-Type Doped GaN Layers Grown on Sapphire

Infrared (IR) reflectance spectroscopy is applied to study Si-doped multilayer n+/n0/n+-GaN structure grown on GaN buffer with GaN-template/sapphire substrate. Analysis of the investigated structure by photo-etching, SEM, and SIMS methods showed the existence of the additional layer with the drastic difference in Si and O doping levels and located between the epitaxial GaN buffer and template. Simulation of the experimental reflectivity spectra was performed in a wide frequency range. It is shown that the modeling of IR reflectance spectrum using 2 × 2 transfer matrix method and including into analysis the additional layer make it possible to obtain the best fitting of the experimental spectrum, which follows in the evaluation of GaN layer thicknesses which are in good agreement with the SEM and SIMS data. Spectral dependence of plasmon-LO-phonon coupled modes for each GaN layer is obtained from the spectral dependence of dielectric of Si doping impurity, which is attributed to compensation effects by the acceptor states.

Structural Modification of Single-Layer Graphene Under Laser Irradiation Featured by Micro-Raman Spectroscopy

Confocal micro-Raman spectroscopy is used as a sensitive tool to study the nature of laser-induced defects in single-layer graphene. Appearance and drastic intensity increase of D- and D′ modes in the Raman spectra at high power of laser irradiation is related to generation of structural defects. Time- and power-dependent evolution of Raman spectra is studied. The dependence of relative intensity of defective D- and D′ bands is analyzed to relate the certain types of structural defects. The surface density of structural defects is estimated from the intensity ratio of D- and G bands using the D-band activation model. Unusual broadening of the D band and splitting of the G band into G− and G+ components with redistribution of their intensities is observed at high laser power and exposition. Position of the G+ band is discussed in relation with nonuniform doping of graphene with charge impurities. Simultaneous presence in the Raman spectra of heavily irradiated graphene of rather narrow G band and broaden D band is explained by coexistence within the Raman probe of more and less damaged graphene areas. This assumption is additionally confirmed by confocal Raman mapping of the heavily irradiated area.

Erratum to: Infrared Reflectance Analysis of Epitaxial n-Type Doped GaN Layers Grown on Sapphire

Author details V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Pr. Nauky 41, Kiev 03680, Ukraine. Institute for Nanoscience and Engineering, University of Arkansas, West Dickson 731, Fayetteville, AR 72701, USA. Institute of High Pressure Physics, Polish Academy of Sciences, Sokolowska str. 29/37, 01-142 Warsaw, Poland. Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, PL-02-668 Warsaw, Poland.

An Experimental Study of Properties of Ultrathin Si Layer with Bonded Si/SiO2 Interface

Properties of Si/buried oxide (BOX) systems with bonded interface in silicon-on-insulator (SOI) wafers were studied in this paper. Results show impact of the starting Si material - Czochralski (Cz) or float-zone (Fz) grown silicon on the electron mobility (μe) and BOX charge behavior in ultrathin SOI layers. In particular, there were found: 1) the μe ~ Ne-0.3 dependencies at the electron density Ne in the range of 4х (1011-1012) cm-2 in accumulation Cz-SOI layers with the μe degradation when Si thickness decreases from 20 to 9 nm, and 2) the ~ Ne-0.6 behavior of mobility with no degradation in Fz-SOI layers. Raman spectroscopy shows the structural modification of Cz-SOI layers. An origin of degradation of the electrical and structural properties for ultrathin SOI layer is discussed.