Showing papers by "Lakhdar Dehimi published in 2020"

An optimized Graphene/4H-SiC/Graphene MSM UV-photodetector operating in a wide range of temperature

Abstract: In this paper,. an accurate analytical model has been developed to optimize the performance of an Interdigitated Graphene Electrode/p-silicon carbide (IGE/p-4H-SiC) Metal semiconductor Metal (MSM) photodetector operating in a wide range of temperatures. The proposed model considers different carrier loss mechanisms and can reproduce the experimental results well. An overall assessment of the electrodes geometrical parameters’ influence on the device sensitivity and speed performances was executed. Our results confirm the excellent ability of the suggested Graphene electrode system to decrease the unwanted shadowing effect. A responsivity of 238 μA/W was obtained under 325-nm illumination compared to the 16.7 μA/W for the conventional Cr-Pd/p-SiC PD. A photocurrent to- dark-current ratio (PDCR) of 5.75 × 105 at 300 K and 270 at 500 K was distinguished. The response time was found to be around 14 μs at 300 K and 54.5 μs at 500 K. Furthermore, the developed model serves as a fitness function for the multi objective optimization (MOGA) approach. The optimized IGE/p-4H-SiC MSM-PD design not only exhibits higher performance in terms of PDCR (7.2 × 105), responsivity (430A/cm2) and detectivity (1.3 × 1014 Jones) but also balances the compromise between ultrasensitive and high-speed figures of merit with a response time of 4.7 μs. Therefore, the proposed methodology permits to realize ultra-sensitive, high-speed SiC optoelectronic devices for extremely high temperature applications.

Simulation analysis of a high efficiency GaInP/Si multijunction solar cell

Abstract: The solar power conversion efficiency of a gallium indium phosphide (GaInP)/silicon (Si) tandem solar cell has been investigated by means of a physical device simulator considering both mechanically stacked and monolithic structures. In particular, to interconnect the bottom and top sub-cells of the monolithic tandem, a gallium arsenide (GaAs)-based tunnel-junction, i.e. GaAs(n+)/GaAs(p+), which assures a low electrical resistance and an optically low-loss connection, has been considered. The J–V characteristics of the single junction cells, monolithic tandem, and mechanically stacked structure have been calculated extracting the main photovoltaic parameters. An analysis of the tunnel-junction behaviour has been also developed. The mechanically stacked cell achieves an efficiency of 24.27% whereas the monolithic tandem reaches an efficiency of 31.11% under AM1.5 spectral conditions. External quantum efficiency simulations have evaluated the useful wavelength range. The results and discussion could be helpful in designing high efficiency monolithic multijunction GaInP/Si solar cells involving a thin GaAs(n+)/GaAs(p+) tunnel junction.

Modelling and performance analysis of a GaN-based n/p junction betavoltaic cell

Abstract: In this work, we optimized the performance of a gallium nitride (GaN)-based n/p junction betavoltaic cell irradiated by the radioisotope nickel-63 ( N i 63 ). In particular, we developed a lab-made software starting from an analytical model that takes into account a set of fundamental physical parameters for the cell structure. The simulations reveal that, by using a N i 63 radioisotope source with a 25 mCi/cm 2 activity density emitting a flux of beta-particles with an average energy of 17.1 KeV, the cell performs a conversion efficiency ( η ) in excess of 26%, thus approaching the theoretical limit for a GaN-based device. The other electrical parameters of the cell, namely the short-circuit current density ( J s c ), open-circuit voltage ( V o c ), and maximum electrical power density ( P m a x ) are 240 n A ∕ c m 2 , 2.87 V, and 660 n W ∕ c m 2 , respectively. The presented analysis can turn useful for understanding the theoretical background needed to better face GaN-based betavoltaic cell design problems.

Analysis of the Electrical Characteristics of Mo/4H-SiC Schottky Barrier Diodes for Temperature-Sensing Applications

Abstract: The experimental forward current–voltage–temperature (ID–VD–T) characteristics of Mo/4H-SiC Schottky barrier diodes are investigated by means of a careful simulation study. The simulations are in excellent agreement with measurements in the whole explored current range extending over ten orders of magnitude for temperatures from 303 K to 498 K. The diode ideality factor tends to decrease while the Schottky barrier height increases with increasing temperature. These variations are explained on the basis of the thermionic emission theory with a Gaussian distribution of the barrier height around the Mo/4H-SiC interface. The calculated Richardson constant is A* = 155.78 A cm−2 K−2 which is very close to the theoretical value of 146 A cm−2 K−2 expected for n-type 4H-SiC. The linear dependence of VD on temperature is also investigated for several bias currents. The obtained results reveal that the device is well suited for temperature-sensing applications, showing a good coefficient of determination (R2 = 0.99974 for 100 nA ≤ ID ≤ 1 mA) and a high sensitivity (S = 1.92 mV K−1 for ID = 1 μA). The temperature error between the voltage measurements and their linear best fit is lower than 1.5 K.

Modelling and optical response of a compressive-strained AlGaN/GaN quantum well laser diode

Abstract: The effects of the quantum well (QW) width, carrier density, and aluminium (Al) concentration in the barrier layers on the optical characteristics of a gallium nitride (GaN)-based QW laser diode are investigated by means of a careful modelling analysis in a wide range of temperatures. The device’s optical gain is calculated by using two different band energy models. The first is based on the simple band-to-band model that accounts for carrier transitions between the first levels of the conduction band and valence band, whereas the second assumes the perturbation theory (k.p model) for considering the valence intersubband transitions and the relative absorption losses in the QW. The results reveal that the optical gain increases with increasing the n-type doping density as well as the Al molar fraction of the AlxGa1–xN layers, which originate the GaN compressive-strained QW. In particular, a significant optical gain on the order of 5000 cm–1 is calculated for a QW width of 40 A at room temperature. In addition, the laser threshold current density is of few tens of A/cm2 at low temperatures.

Analysis of 4H-SiC MOSFET with distinct high-k/4H-SiC interfaces under high temperature and carrier-trapping conditions

Abstract: In this work, the reliability of different oxide/4H-SiC interfaces under high temperature and carrier-trapping conditions are investigated carefully. In more detail, the carrier-trapping and temperature effects are considered in the electrical characterization of a low breakdown 4H-SiC-based MOSFET by using in turn SiO2, Si3N4, AlN, Al2O3, Y2O3 and HfO2 as gate dielectric. A gate oxide with a high relative permittivity notably improves the transistor performance. In addition, HfO2 assures the MOSFET best immunity behaviors. The obtained results are explained in terms of the carrier channel mobility, device on-state resistance, and oxide electric field. By using HfO2, however, an increased gate leakage current is calculated. This drawback is overcome by inserting a thin interfacial layer (2 nm-thick) in the HfO2/4H-SiC MOS structure. In particular, two alternative gate stacked dielectrics, involving either SiO2 or Al2O3, have proven their effectiveness in preserving the transistor on-state figures of merit while limiting the gate leakage current in the whole explored gate voltage range. To support the prediction capabilities of the presented modeling analysis, the simulations results are compared with experimental data from literature resulting in a good agreement. Low power MOSFETs are used in several applications for which reliability and durability are as critical as performance. For example, referring to power optimizers for photovoltaic (PV) modules, which fall under the low-load and low-voltage category of DC–DC converters, these devices significantly increase the energy generated by each single PV module operating under harsh conditions and stressing environments. In addition, they have to ensure high reliability over the long term of operation.

Performance Evaluation and Comparison of Monolithic and Mechanically Stacked Dual Tandem InGaP/GaAs Heterojunction on Ge Cell: A TCAD Study

Abstract: The photovoltaic characteristics of a mechanically and monolithic stacked tandem solar cell of the heterojunction InGaP/GaAs and Ge sub cells, were numerically simulated under 1-sun air mass 1.5 global spectrum (AM1.5G) at ambient temperature (300 K) using the two-dimensional device simulator Silvaco–Atlas. Our tandem structure consists of a thin upper cell with heterojunction of indium and gallium phosphide on gallium arsenide (In0.49Ga0.51P/GaAs), on a relatively thick germanium (Ge) substrate which acts as a lower cell in order to obtain good performances of such a structure. We studied both cells, stacked mechanically (four terminal:4T) and monolithic (two terminal:2T) using Silvaco ATLAS Virtual Wafer FabricationTool. First, we have simulated the single InGaP/GaAs and Ge solar cells with fixed thicknesses at 1.4 µm and 210 µm respectively. They presented a conversion efficiencies (ƞ) of 30.32% and 10.96% respectively. The efficiency of mechanically stacked tandem solar is 30.96% and short current density of 26.16 mA/cm2 which is limited by the lower short current density of both sub-cells. Using the method of current matching, by varying the base thicknesses of the InGaP/GaAs top and Ge bottom sub-cells, the numerical simulation results presented a matched maximum current Jsc value of 29.12 mA/cm2 obtained at base thicknesses of 0.605 and 209.9 μm for the InGaP/GaAs top and Ge bottom sub-cells respectively, leading to a high power conversion efficiency (ƞ) of the mechanically stacked sub cells of 34.77%, the open-circuit voltage and the fill factor are 1.329 V and 88.96%, respectively. Next, the sub-cells were interconnected with tunnel junctions (TJs), p-GaAs/n-GaAs to allow carrier transport, the results of the monolithic stacked sub-cells are converged with results of the mechanically stacked sub-cells, and are represented in the following results of the tandem cell: power conversion efficiency (ƞ) of 32.96%, the open-circuit voltage of 1.343 V, the short current of 29.19 mA/cm2 and the fill factor of 84.05%.