1,537 research outputs found
AC Conductance in Dense Array of the GeSi Quantum Dots in Si
Complex AC-conductance, , in the systems with dense
GeSi quantum dot (QD) arrays in Si has been determined from
simultaneous measurements of attenuation, ,
and velocity, , of surface acoustic waves (SAW)
with frequencies = 30-300 MHz as functions of transverse magnetic field 18 T in the temperature range = 1-20 K. It has been shown that in the
sample with dopant (B) concentration 8.2 cm at
temperatures 4 K the AC conductivity is dominated by hopping between
states localized in different QDs. The observed power-law temperature
dependence, , and weak frequency dependence,
, of the AC conductivity are consistent with
predictions of the two-site model for AC hopping conductivity for the case of
1, where is the SAW angular frequency and
is the typical population relaxation time. At 7 K the AC
conductivity is due to thermal activation of the carriers (holes) to the
mobility edge. In intermediate temperature region 4 7 K, where AC
conductivity is due to a combination of hops between QDs and diffusion on the
mobility edge, one succeeded to separate both contributions. Temperature
dependence of hopping contribution to the conductivity above 4.5 K
saturates, evidencing crossover to the regime where 1. From
crossover condition, = 1, the typical value, , of
the relaxation time has been determined.Comment: revtex, 3 pages, 6 figure
Crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) and luminescence of Eu(2+) in the crystals
Within the framework of the virtual crystal method implemented in the shell
model and pair potential approximation the crystal structure of mixed fluorites
Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) has been calculated. The impurity center
Eu(2+) and the distance Eu(2+)-F in this crystals have been also calculated.
The low level position of excited 4f65d configuration of the Eu(2+) ion has
been expressed using phenomenological dependence on distance E(2+)-F. The
dependences of Stokes shift and Huang-Rhys factor on concentration x have been
received for yellow luminescence in Sr(1-x)Ba(x)F(2):Eu(2+). The value x, for
which the eg -level of Eu(2+) ion will be in conduction band in
Sr(1-x)Ba(x)F(2):Eu(2+) has been calculated.Comment: 8 pages, 3 figures. The manuscript is sent to journal 'Physics of the
solid state'. The results will be submitted on inernational conference
SCINTMAT'2002 in oral session (june,20-22,2002,Ekaterinburg,Russia).
Corresponding author e-mail: [email protected]
Influence of the preliminary annealing conditions on step motion at the homoepitaxy on the Si(100) surface
In this paper, the motion of steps SA and SB on the Si(100) surface in the process of Si Molecular beam epitaxy (MBE) is explored. The study was carried out by means of the reflection intensity dependence behavior analysis of reflection high-energy electron diffraction (RHEED) corresponding to the (2×1) and (1×2) reconstructions. Superstructural rearrangement from a two-domain to a single-domain surface is associated with the bilayer step formation, which occurs due to the different motion rates of the steps SA and SB. Based on the research conducted, the conditions under which the step doubling occurs were determined. A behavior analysis of the diffraction reflection intensity dependences showed that an increasing of preliminary annealing time and temperature facilitates to the faster convergence of the steps SA and SB, but to the slower recovery of the initial surface. The presented experimental results indicate that step movement rate difference depends on the step A edge kink density
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