Corresponding author(s):
P. Bury - Department of Physics, Zilina University, 010 26 Zilina, Slovakia
Abstract:
The acoustoelectric interaction between a longitudinal acoustic wave and
heterojunctions is used to investigate the deep centers in GaAs/AlGaAs
heterostructures. The acoustoelectric response generated by the interface
when acoustic wave propagates through the heterostructure reflects any
changes in the charge distribution, connected also with the charged traps.
The time developments of the acoustoelectric response after an optical
excitation pulse reflect then relaxation processes associated with the
thermal recombination of excited carriers moving towards their equilibrium
state. The measured signal that is proportional to the nonequilibrium
carrier density in the interface regions and can be used to the
determination of activation energy and corresponding cross-section of deep
centers. Planar GaAs/AlGaAs heterostructures with both two dimensional
electron system (2 DES) and two dimensional hole system (2 DHS) were
investigated by optically induced acoustic deep-level transient spectroscopy
(OI A-DLTS). The method of computer evaluation of isothermal acoustoelectric
transients was used in the A-DLTS technique. Several deep centers were found
and their parameters were determined.
Passivation of defect states in Si and Si/SiO2 interface states by cyanide treatment: Improvement of characteristics of Pin-junction amorphous Si and crystalline Si-based metal-oxide-semiconductor junction solar cells
Author(s):
N. Fujiwara, T. Fujinaga, D. Niinobe, O. Maida, M. Takahashi, H. Kobayashi
Corresponding author(s):
N. Fujiwara - Institute of Scientific and Industrial Research,
Osaka University and CREST, Japan Science and Technology
Corporation, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
Abstract:
Defect states in Si can be passivated by cyanide
treatment which simply involves immersion of Si materials in KCN
solutions, followed by rinse. When the cyanide treatment is
applied to pin-junction amorphous Si (a-Si) solar cells, the
initial conversion efficiency increases. When the crown-ether
cyanide treatment using a KCN solution of xylene containing
18-crown-6 is performed on i-a-Si films, decreases in the photo-
and dark current densities with the irradiation time are
prevented. The cyanide treatment can also passivate interface
states present at $\rm Si/SiO_{2}$ interfaces, leading to an
increase in the conversion efficiency of $\rm
\langle ITO/SiO_{2}/Si(100)\rangle $ solar cells. Si-CN bonds formed by the
reaction of defect states with cyanide ions have a high bond
energy of about 4.5 eV and hence heat treatment at $\rm
800^{\circ}C$ does not rupture the bonds, making thermal stability
of the cyanide treatment. When the cyanide treatment is applied to
ultrathin $\rm SiO_{2}/Si$ structure, the leakage current density
is markedly decreased.
Chemical etching of mono and poly-crystalline silicon in HF/K2Cr2O7/H2O solutions
In this work an experimental study on the etching reaction of low-doped
silicon was carried out in HF/K$_{2}$Cr$_{2}$O$_{7}$/H$_{2}$O mixed
solutions. The morphology of the etched surface was examined with varying HF
and K$_{2}$Cr$_{2}$O$_{7}$ concentration, reaction time and agitation speed.
The surface of etched wafers were analysed using SEM (scanning electron
microscope) and EDX (Energy-dispersive X-ray). The structure of porous
silicon films created by etching in HF/K$_{2}$Cr$_{2}$O$_{7}$ is shown to
depend on the solution composition and the resistivity of the silicon
substrate. The investigation of the HF/K$_{2}$Cr$_{2}$O$_{7}$ system on
polycrystalline silicon surface shows that in the concentration range 1
$\div $ 2 M of potassium dichromate (K$_{2}$Cr$_{2}$O$_{7})$, the surface is
microporous. The texture developed is a network of hemispherical tubs. It is
seen that reflection losses in micropores (tubs) decreased greatly, to be
comparable with the defect etchants method and much lower that obtained by
Stocks et al. Simultaneous porous silicon growth and deposition of
hexafluorosilicates has been observed. Taking into account this observation
a dissolution mechanism of the silicon is proposed.
Genetic algorithm approach to thin film optical parameters determination
Optical parameters of thin films are important for several optical and
optoelectronic applications. In this work the genetic algorithm method is
proposed to solve optical parameters of thin film values. The experimental
reflectance is modelled by the Forouhi -- Bloomer dispersion relations. The
refractive index, the extinction coefficient and the film thickness are the
unknown parameters in this model. Genetic algorithm use probabilistic
examination of promissing areas of the parameter space. It creates
a~population of solutions based on the reflectance model and then operates
on the population to evolve the best solution by using selection, crossover
and mutation operators on the population individuals. The implementation of
genetic algorithm method and the experimental results are described too.
Atomic force microscopy characterization of ZnTe epitaxial films
In this paper results of a characterization of the surfaces of ZnTe epitaxial
thin films exhibiting the different thicknesses are presented. The results
mentioned are obtained using the procedures enabling us to determine the
values of the following quantities: mean grain size, grain size distribution,
root--mean square values of the heights of the irregularities and
the diagram describing the distribution of the directions of the normals.
For the analysis of the grain structure a watershed algorithm is used.
It is shown that the values of these quantities can describe the morphology
of the ZnTe film surfaces in a sufficient way. Further, it is shown that the
structure of the surfaces of the ZnTe films exhibit facets forming
a grain structure. Moreover, it is presented that the ZnTe film surfaces
exhibit a strong slope anisotropy and that the linear dimensions of
the grains increase with increasing values of the thicknesses of the
ZnTe films.
Relation between photovoltaic characteristics and acceptor concentration at the interface of indium oxide/indium phoshide heterojunction solar cell
Photovoltaic characteristics of a heterojunction solar cell
composed of reactively evaporated indium oxide ($\rm{In_2O_3}$) film and
single crystalline p-type indium phosphide (InP) was found to depend
on acceptor concentration at the interface.
The value of acceptor concentration was preferable to be high
to obtain a high performance cell because larger open-circuit voltage
can be obtained due to decrease
of diode saturation current of the cell with the increase of the acceptor concentration.
The acceptor concentration of the cell was increased by annealing during forming an
ohmic contact. The increase of acceptor concentration by annealing thought to be
able to explain in terms of outdiffusion of the interstitial
zinc atoms in InP bulk.
Further, the value of acceptor concentration is modified by substrate heating
during deposition of transparent and conductive $\rm{In_2O_3}$
film. In order to produce a high performance cell,
low substrate temperature ($200^{\circ}$C) was preferable during
deposition of $\rm{In_2O_3}$.
Regular Papers
Biquaternionic representations of angular momentum and Dirac equation
In the present article, after defining biquaternions, the general
properties of biquaternion's algebra are introduced. The matrix
representations of biquaternions are presented, as well. Then, the
biquaternionic angular momentum is reformulated in terms of biquaternionic
product. A new biquaternionic definition of the Dirac equation and its
solution are given by the use of biquaternion's basis.
The quaternionic energy conservation equation for acoustic
After introducing the quaternions and its algebra, the equations of
the linear acoustics are defined. The local conservation equation for energy
of the linear acoustics using quaternions and a quaternionic first-order
Lagrangian description is then formulated. Using the variational principle,
the local conservation equation for the energy is derived from the
quaternionic gauge transformation. The purpose is to provide an alternative
for the usual derivations.
Electron beam dose calculation: Hybrid pencil beam model extended for small fields
Corresponding author(s):
Luo ZhengMing - Key Lab for Radiation Physics and Technology of the Education Ministry of China and Institute of Nuclear Science and Technology, Sichuan University Chengdu, 610064, P.R. China
Abstract:
The hybrid electron pencil beam model (HPBM) can usually be applied to
middle or large fields and get good results, whereas it is sometimes not so
successful to apply HPBM to small fields. In this note we report some results
obtained by using an extended hybrid electron pencil beam model for small
fields. Considering the condition of small fields, we redefine the central-axis
depth dose for mono-energetic electrons in small fields and calculate the fitted
spectrum of incident electron beam for these small fields. Through these
improvements, we can make the extended hybrid electron pencil beam model
applicable to small fields and obtain good results. And at the same time, the
extended HPBM retains the calculation accuracy and efficiency for middle and
large fields.
