Gazimagomed N Aliev

Hypersonic acoustic mirrors and microcavities in porous silicon

Periodic solid state structures exhibit transmission stop bands for waves of certain frequencies. We report the realization and direct measurement of acoustic band gaps in porous silicon multilayer structures which exhibit ∼50u2002dB stop bands for longitudinal acoustic waves in the gigahertz range. Furthermore, realization of an acoustic microcavity structure in porous silicon is demonstrated.

Elastic properties of porous silicon studied by acoustic transmission spectroscopy

The porosity dependence of the elastic properties of porous silicon in different crystallographic directions is studied. The velocity of longitudinal acoustic waves in porous silicon layers electrochemically etched in (100), (110), and (111) oriented wafers has been measured by acoustic spectroscopy in the gigahertz frequency range. This non-destructive method was used for porous silicon layers with porosity of 25-85% obtaining velocities in the range of about 1 to 7 km s-1. The implication of constant Poisson’s ratio of porous silicon is examined. The effect of velocity dispersion due to multiple scattering is considered. The c11 stiffness constant can be obtained from the velocity measurement in the [100] direction of a cubic crystal. We show that, using the results for velocity in [110] or [111] directions and Keating’s relation, the stiffness constants c12 and c44 can be obtained. The velocity dependence on porosity was fitted as v=v0(1-φ)κ, where v0 is the velocity in bulk silicon, φ is porosity, and...

Hypersonic rugate filters based on porous silicon

Periodic solid state structures exhibit transmission stopbands for waves of certain frequencies. We demonstrate porous silicon based rugate filters with 40 dB rejection first-order stopbands for longitudinal acoustic waves at hypersonic frequencies and the predicted suppression of higher order bands.

Origin of the red luminescence in Mg-doped GaN

Optically detected magnetic resonance and positron annihilation spectroscopy experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective-mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects.

Experimental and theoretical demonstration of acoustic Bloch oscillations in porous silicon structures

We report the theoretical calculations and the experimental demonstration of acoustic Bloch oscillations and Wannier-Stark ladders in linear tilted multilayer structures based on porous silicon. The considered structures consist of layers with constant porosity alternated by layers with a linear gradient in the parameter η=1/vL2 along the growth direction in order to tilt the acoustic band gap. The purpose of this gradient is to mimic the tilted electronic miniband structure of a superlattice semiconductor under an external electric field. In this way, acoustic Wannier-Stark ladders of equidistant modes are formed and they were experimentally confirmed in the transmission spectrum around 1.2u2009GHz. Their frequency separation defines the period of the acoustic Bloch oscillations. We fabricated three different structures with the same thicknesses but different values in the η parameter to observe the effect on the period of the Bloch oscillations. We measured the acoustic transmission spectra in the frequency...

Spin-flip Raman scattering studies of ZnSe bulk crystals doped with antimony

We have used spin-flip Raman scattering and photoluminescence to investigate ZnSe crystals doped with antimony, which is a potential p-type dopant. The experiments provide evidence for the existence of a shallow acceptor level at about 70 meV above the valence band and for the presence of a previously unreported deep donor level at about 55 meV below the conduction band. As in ZnSe doped with nitrogen, it is possible that the formation of such deep-donor states may be an inevitable consequence of high concentrations of p-type dopants and that the resulting compensation may be one of the reasons why attempts to obtain p-type conductivity continue to be difficult.