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The dark current–voltage characteristics I−V of the fabricated Au/a-Si:H(n+)/SiGe(n) /c-Si(p)/Ag hetero-junction are investigated at temperatures ranging from 80 to 300 K to determine the carrier t...

In the present paper, we report a combined experimental and theoretical study of compositionally graded Si1−xGex thin films grown on Si at 550°C. The study has been conducted for two particular val...

Polycrystalline of La 0 . 5 Pr 0 . 2 Sr 0 . 3 Mn (1−x) Fe x O 3 (x = 0, 0.15 and 0.2) samples have been elaborated by the self-combustion reaction method. Single-phase compound formation was confirmed by preliminary X-ray structural analysis. Detailed studies of the electric and dielectric properties of the compound in the frequency range from 100 Hz to 1 MHz and temperatures between 100 and 400K were investigated using the impedance spectroscopy technique. The results show that all samples exhibit dependence of both ac and dc conductivity on the iron content. Furthermore, the values of dielectric loss, dielectric loss tangent, real and imaginary parts of the impedance, real and imaginary parts of the electrical modulus, ac and dc electrical conductivity were found considerably sensitive to both temperature and applied frequency.

SiGe thin films with different Ge fraction were obtained by Molecular Beam Epitaxy (MBE) on silicon (001) substrates. The SiGe thin films properties are obtained using Spectroscopic Ellipsometry (SE) in the frame of the New Amorphous model. This model demonstrates that depending on the Ge fraction high absorption coefficients of order 106 cm−1 were obtained. The solar cell performance of SiGe/Si heterostructures was measured using a JASCO YQ-250BX system with light source of AM 1.5 solar simulator. The experimental results obtained (y = 0.15, Wa-Si: H = 2 nm) yielded to an improvement of about 1.3 mA cm−2 for the short-circuit current density, and about 2.2% for the cell efficiency compared to the conventional cell i.e. without a-Si:H thin layer (FSF).

The structural and electronic properties of the bulk GaAs and Ge semiconductor and the band offsets for the GaAs/Ge and AsGa-Ge interfaces are investigated by density functional theory (DFT). This calculation has shown that the lattice parameter is underestimated by the local density (LDA) approximation and overestimated by the generalized gradient approximation (GGA). An opposite behavior is observed for the bulk modulus B 0 . Concern, the super-lattice GaAs/Ge (001), studied in our work, we found that the substitution of the atom of the interface affects the discontinuity of the VBO valence band, which is mainly due to the different electronic charges accumulated in the interfaces.

The present paper accounts for a simulation study carried out to determine and optimize the effect of the high---low junction emitter front surface field (FSF) of thin heterojunction solar cell $$\text {n}^{+}$$n+(a-Si: H)/n(SiGe)/p(Si)). A theoretical model describing the behavior of heterojunction $$\text {n}^{+}$$n+---n---p type solar cells has been proposed. Besides, the expression of the photovoltaic equations allowing for the obtention of the optimal quantum efficiency of the solar cells based on the suggested model has been given. The effects of the a-Si:H-layer thickness and Ge fraction are discussed, using the computed results. The main role of an FSF layer is to reduce the effect of front surface recombination and the enhancement of light-generated free carriers' collection. This is primarily responsible for the increase of the spectral response compared with the conventional solar cell. This is achieved by the drastic reduction of the effective recombination at the emitter upper boundary and the optimum value of $$\text {n}^{+}$$n+ layer thicknesses (a-Si:H) is about 2 nm.

This work presents an experimental study of the electrical and dielectric properties of $$ {\text{Si}}_{1 - y} {\text{Ge}}_{y} $$ thin films for solar cells application. In order to through light in the electrical conductivity and dielectric properties of the heterojunction, we have carried out the complex impedance spectroscopy technique in the frequency range 10 kHz–1 MHZ at room temperature. The values of the dielectric constant, the real and the imaginary parts of electrical impedance and AC electrical conductivity were found considerably sensitive to frequency. We also studied the photovoltaic parameters of Au/n(SiGe)/p(c-Si) heterojunction solar cell with (y = 0.2). The experimental results show an open-circuit voltage about 0.82 V, a short-circuit current density about 2.1 (mA/cm2) and an efficiency of the cell about 1.3%. The results indicate that the Au/n(SiGe)/p(c-Si) heterojunction structure might be promising for the solar cell applications.

The dark current–voltage of the Au/n+(a-Si:H)/n(SiGe)/p(c-Si)/Ag heterojunction structure have been investigated in order to determinate the electrical conduction mechanisms. The forward current at different temperatures was found to be increased exponentially at low applied voltage $$(V \le 0.4 {\text{V}})$$ indicating that the conduction mechanism of the diode was controlled by the thermionic emission mechanism. While, at bias voltages higher than 0.5 V, the results obtained show that the carriers conduction was described by the space charge limited current mechanism. The effect of front surface field (FSF) on the photovoltaic parameters of Au/n+ (a-Si:H)/n(SiGe)/p(c-Si) heterojunction solar cell is studied. The experimental results obtained yielded to an improvement of about 50 mV for the open-circuit voltage, 1.1 mA cm−2 for the short-circuit current density, and about 1% for the cell efficiency compared to the conventional cell i.e. without a-Si:H thin layer (FSF).

In this paper we study the growth of SiGe thin films (n-type) on c-Si substrate (p-type) by Molecular Beam Epitaxy. High resolution Raman spectroscopy atomic force microscopy and X-ray diffraction are used to characterize the thin epitaxial layers of n-type SiGe thin films. The refractive index $$n\left( \lambda \right)$$ and the extinction coefficient $$k\left( \lambda \right)$$ of SiGe thin films with various Ge fractions are determined using spectroscopic ellipsometry in the frame of the Forouhi and Bloomer model. The simulation study shows that the refractive index decreases with Ge fraction in the U–V range whereas, the extinction coefficient increases in the visible region. The experimental extracted Eg of SiGe agrees well with the theoretical calculation on the strained SiGe material. The luminescence is characterized by a broad PL band centered at 779 nm.

The present paper reports on a simulation study carried out to determine and optimize the effect of the high-low junction emitter (n+/n) of thin film SiGe/Si solar cell. The model is based on a simple analytical approach that draws on relevant device physics, including effective surface recombination velocity at the high-low junction and band discontinuities associated with heterojunctions. The collection of the light absorbed by the front surface field is discussed and an analytical solution is derived for the light-generated current in this layer. The photovoltaic parameters of SiGe/Si solar cells and those of the conventional cell Si/Si are compared. The findings revealed that the addition of Ge ~15 % to crystal Si highly enhances short-circuit current density and cell efficiency, whereas the SiGe band-gap degrades particularly the open-circuit voltage. The results also indicate that the solar cell maximum efficiency increase by about 1.7 % when the interface state density is lower than 1011 cm−2.