M. Fathallah

Dynamic behavior of Ti/4H-SiC Schottky diodes

The wide band gap (3.2 eV) allows the silicon carbide (SiC) to work at high temperatures with high voltages and currents, to switch large power densities and reduce losses. The 4H-SiC polytype is the most widely used material for electronic applications. Despite the development of manufacturing technology of SiC wafers, this material has structural defects, such as micropipes, dislocations and inclusions of polytypes. In this paper, the defects and dynamic performance of the SiC Schottky diodes is studied and the obtained maximum reverse voltage is 600V. The reverse recovery time is evaluated to 135ns. The results demonstrate the effectiveness of the SiC devices in reducing the overall system losses generated by switching transitions compared to silicon based diodes. We introduced the parameters found in the Ti/4H-SiC Schottky diode in the Pspice model for simulation. We compared these results with the model using Matlab-Simulink to see the behavior of the switching cell and to deduce the equivalent circuit of diode in dynamic transitions.

Photoinduced defects in wide-gap materials: Hydrogenated amorphous silicon-carbon and silicon-nitrogen films

Abstract Wide-bandgap hydrogenated amorphous silicon-carbon and silicon-nitrogen films having optical gaps in the range 1.9–4.0eV have been deposited by the 13.56 MHz plasma-enhanced chemical vapour deposition technique from SiH4 + C2H2 (+H2), SiH4 + NH3 (+H2), gas mixtures. The deposition conditions have been chosen so as to obtain device-quality films already successfully applied in optoelectronic technology. The films have been light soaked in the average weather conditions solar spectrum (air mass 2.0) for times up to 90 h, monitoring the absorbed energy. The optical properties have been measured after each occurrence of damage, and the defect density evolution due to light soaking was determined by photothermal deflection spectroscopy. An increase in the density of defects with light exposure was observed in all samples strongly dependent on carbon or nitrogen gas sources, plasma conditions and initial properties.

Study of the optical properties and the density-of-states distribution of hydrogenated amorphous silicon-nitrogen alloy

Abstract The constant-photocurrent method (CPM) and photothermal deflection spectroscopy (PDS) have been used as complementary techniques to measure the density-of-states distribution and the different optical parameters in hydrogenated amorphous silicon-nitrogen alloy (a-SiN:H). Constants such as the optical gap E g the Urbach edge E u or valence-band edge E 0V were obtained directly from the CPM or photothermal deflection spectra. The height of the midgap-defect density of States, its wideness or the conduction-band edge have been deduced by applying a deconvolution procedure to the measured absorption spectra. The density of surface states was also calculated. The results were based on the different sensitivities of the CPM and PDS to transitions involving unoccupied defects and surface states. We have studied the influence of nitrogen incorporation in a-SiN: H samples and the effect of hydrogen dilution.

Barrier height evolution in a non-uniform interface of Ti or Mo Schottky diodes based on 4H-SiC

The characteristics of titanium (Ti) or molybdenum (Mo) as Schottky contact of device based on 4H-SiC material were investigated. The parameters deduced from static characterisation of Ti/4H-SiC show an increase of barrier height (ϕB) from 0.76 to 1.26 eV and a decrease of ideality factor (n) from 1.26 to 1.07 when the temperature varies from 10 to 460 K. Whereas in the Mo/4H-SiC the barrier height increases from 0.45 to 1.05 eV and the ideality factor decreases from 2.20 to 1.03. When the temperature decreases, a deformation of J–V characteristics appears for T < 300 K. The current through an inhomogeneous junction has been proposed to be described by a parallel conduction model used when there is a region of different barrier height in a non-uniform interface. The evolution of ϕB and n as function of temperature improves the deviation from typical thermionic model, implying geometry based on circular patches of low Schottky barrier height (SBH) incorporated in a region of higher SBH.