In this paper we report electron beam induced current (EBIC) measurements on Schottky diodes on undoped GaN samples grown by the metal organic vapor phase epitaxy method on porous silicon substrates. A 2D simulation model was applied to...
moreIn this paper we report electron beam induced current (EBIC) measurements on Schottky diodes on undoped GaN samples grown by the metal organic vapor phase epitaxy method on porous silicon substrates. A 2D simulation model was applied to perform the theoretical EBIC profiles and to compare with the experimental one. A minority carrier diffusion length (L) for holes of 0.72
A phenomenological model is proposed for the nematic-smectic A–smectic C transition. Two order parameters which are biquadratically coupled are involved. The first one is primary and characterizes the appearance of layers in the smectic...
moreA phenomenological model is proposed for the nematic-smectic A–smectic C transition. Two order parameters which are biquadratically coupled are involved. The first one is primary and characterizes the appearance of layers in the smectic phases. The second order parameter is triggered by the first one and can be identified with the tilt angle.Analytic expressions are obtained for lines and points
ABSTRACT The tetraethylammonium hexachlorostannate [(C2H5)4N]2SnCl6 undergoes three phase transitions in the temperature range 200–400 K. The high-symmetry phase is described by the space group Fm3m. To carry out the symmetry...
moreABSTRACT The tetraethylammonium hexachlorostannate [(C2H5)4N]2SnCl6 undergoes three phase transitions in the temperature range 200–400 K. The high-symmetry phase is described by the space group Fm3m. To carry out the symmetry relationships between Fm3m and the other observed space groups we introduce two primary order parameters, which transform according to the irreducible representations A2g, Eg of Fm3m at the X high symmetry point. These two order parameters are coupled to explain the symmetry change from Fm3m to a non maximal subgroup, in this case the induced representation is the direct sum A2g ⌖ Eg.
ABSTRACT In this paper, we report the electric investigation of thin nitride gallium films by the capacitance voltage technique and the thermal step method (TSM). The C–V analysis at 1MHz of Au/GaN diode reveals MOS behaviour and shows...
moreABSTRACT In this paper, we report the electric investigation of thin nitride gallium films by the capacitance voltage technique and the thermal step method (TSM). The C–V analysis at 1MHz of Au/GaN diode reveals MOS behaviour and shows strong capacitance hysteresis.This may be due to the presence of trapped charge in this structure. The space charge dynamics is studied by thermal step method at different applied voltages. The TS currents are reverted from negative ones to positive ones above inversion threshold of +0.2V. This change corresponds to charge modulation from accumulation to the inversion one, in good agreement with the C–V characteristics. The stored charge in this sample is related to the nature of gallium nitride and to the manufacturing processes. The results confirm the possibility to apply the TSM for the measurement of the space charge in the semiconductor materials.
We have developed a model for the calculation of the induced current due to an electron beam with an extended generation profile. The analytical expression of the electron beam induced current (EBIC) is obtained by solving the...
moreWe have developed a model for the calculation of the induced current due to an electron beam with an extended generation profile. The analytical expression of the electron beam induced current (EBIC) is obtained by solving the steady-state continuity equation using the Green function method. In the case of a sulphur doped (Ga{0.7}Al{0.3}As:N^+/Ga{0.7}Al{0.3}As:P) sample prepared by metalorganic vapour phase epitaxy
ABSTRACT A new mixed acid sulphate K0.9Rb0.1HSO4 was synthesized at room temperature. It has been firstly characterised by X-ray diffraction (XRD) and vibrational spectroscopy investigations. Then, in order to detect phase transitions and...
moreABSTRACT A new mixed acid sulphate K0.9Rb0.1HSO4 was synthesized at room temperature. It has been firstly characterised by X-ray diffraction (XRD) and vibrational spectroscopy investigations. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by differential scanning calorimetry (DSC), (XRD), electrical conductivity measurements, and impedance spectroscopy were carried out. The XRD results on single crystals showed that at room temperature, K0.9Rb0.1HSO4 has an orthorhombic symmetry with space group Pbca. The unit cell parameters are: a = 8.39(6) Å; b = 9.79(8) Å and c = 18.98(5) Å. The Raman and infrared spectra at room temperature were also investigated. The structural similarity with KHSO has been confirmed. The thermal studies showed that K0.9Rb0.1HSO4 undergoes two structural phase transitions at about 400 K and 435 K. A partial substitution of K+ by Rb+ increases the conductivity even at room temperature. The transition at 435 K leads to a super-ionic conductor state at high temperatures related with rotational motions of HSO4 − ions.
ABSTRACT In the frame of the thermal step method (TSM) used to characterize the space charge in dielectric materials, we present an original numerical technique for determining the electric field distribution in the bulk of a dielectric...
moreABSTRACT In the frame of the thermal step method (TSM) used to characterize the space charge in dielectric materials, we present an original numerical technique for determining the electric field distribution in the bulk of a dielectric plate or cable. The first stage of our technique is the application of the finite element method (FEM) in order to find instantaneous distributions of temperature profiles. The calculation of the electric field distribution is based on these obtained profiles. During the stage of the determination, our mathematical treatment is based on the TSM charge q(t) in order to avoid numerical instabilities on the temperature derivatives. Therefore, we have transformed the integral equation for the TSM current I(t) used in previous works to an integral equation for the TSM charge q(t). The control of the instantaneous propagation of the thermal wave front, produced by submitting one face of the dielectric to a thermal step, and the application of Simpson's method to the integral equation of the TSM charge q(t), allow to determine the electric field distribution. The results of the electric field distribution are validated with those obtained in previous works. A good agreement and an improvement near the dielectric thickness boundaries are observed on these results. The numerical space charge density within the material is obtained by numerical derivation of the field according to Poisson's equation.
We have developed a model of calculation of the induced current due to an electron beam. The expression for the electron beam induced current (EBIC) with an extended generation profile is obtained via the resolution of a steady state...
moreWe have developed a model of calculation of the induced current due to an electron beam. The expression for the electron beam induced current (EBIC) with an extended generation profile is obtained via the resolution of a steady state continuity equation by the Green function method, satisfying appropriated boundary conditions to the physical model. The generation profile takes into account
ABSTRACT The mixed sulphate acid Rb{0.7}(NH{4}){0.3}HSO{4} presents at room temperature a phase with a structure similar to the one of the parent compounds RbHSO{4} and NH{4}HSO{4}. Different techniques of the study of phase transitions...
moreABSTRACT The mixed sulphate acid Rb{0.7}(NH{4}){0.3}HSO{4} presents at room temperature a phase with a structure similar to the one of the parent compounds RbHSO{4} and NH{4}HSO{4}. Different techniques of the study of phase transitions show that this compound exhibits five phases with varying temperature and in particular the appearance of a new phase (noted IV) in comparison of the phase diagram of parent compounds, this phase takes place in the range of temperature T between 330 and 435 K. The symmetry of the mixed compound at room temperature (phase III) has been performed again by X-ray diffraction on single crystals. The crystallographic characterization of the phase IV is made by X-ray diffraction on powder sample. Crystallographic parameters in this phase are then obtained whereas group theory considerations gives the most probable space group of this phase. In this work, the phase transitions are studied by dielectric measurements. Theoretical study of the behaviour of dielectric susceptibility based on LANDAU theory of phase transitions shows an improper ferroic character of the transition occurring at 330 K with a faintness index f equal to 2.
