R. Gharbi

Light soaking in a-SiC:H films grown by PECVD in undiluted and hydrogen diluted SiH4+CH4 gas mixtures

Abstract Amorphous silicon carbon alloys having an energy gap in the range 2.0–2.5 eV were deposited by plasma enhanced chemical vapor deposition (PECVD) from undiluted and hydrogen diluted SiH 4 + CH 4 mixtures. The optoelectronic and compositional properties of the samples were measured. Light soaking till saturation was performed on the samples and the effect on defect densities and photoconduction was investigated for both the diluted and undiluted sets of samples. The dilution in hydrogen of the gas mixtures produces samples with higher carbon incorporation, lower defect density and a lower degradation of the optoelectronic properties under light soaking.

Effect of defects on the efficiency of a-SiC:H p-i-n based solar cells

In amorphous hydrogenated silicon carbide (a-SiC:H) based p-i-n type solar cells, the device performance is limited by various factors. Most important of which is defects in the i-layer and particularly in the p/i interface. We performed I-V measurements on amorphous solar cells in the structure p(a-SiC H)/i(a-SiC:H)/n(a-Si:H) at AM1.5. All parameters are determined such as efficiency and filling factor. In the dark, the static and dynamic parameters of diode are deduced. Defects in the intrinsic layer are evaluated by photothermal deflexion spectroscopy technique. All the measured parameters are used by the solar cell capacitance simulator (SCAPS 3.2). The structure of solar cells and the experimental conditions were introduced in simulator. The experimental I-V and spectral response characteristics were correlated to the simulated ones. The simulation shows that increase in defects density, reduces the electrical parameters of amorphous solar cells. The effect of the gap value is more important to define the efficiency of the solar cell made by a-SiC:H materials.

Properties of amorphous carbon nitride prepared by RF reactive sputtering

The local microstructure and optical and electrical properties were investigated of amorphous carbon nitride (a-CN) films deposited by reactive radio-frequency (RF) sputtering. Two series prepared in nitrogen or in a nitrogen and argon mixture were studied. The optical properties were investigated by transmittance/reflectance and photothermal deflection spectroscopies. Combined infrared measurements and Raman scattering spectroscopies were used to investigate the microstructure of a-CN films in terms of nitrogen incorporation within the films and C sp 2 content. These experiments were completed by dark electrical conductivity measurements performed in coplanar configuration in the temperature range 50–450 K. The films exhibit semiconductor behaviour and the temperature dependence suggests two types of conduction. An increase in nitrogen incorporation induces an increase with clustering of sp 2 phase replacing C=C olefinic groups with aromatic groups.

Light induced defects in amorphous silicon-carbon alloys a-SiC:H

Abstract Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + SiH 4 with and without hydrogen dilution. The CH 4 fraction in the plasma was varied between 40 and 95%. The energy gap of our samples varies between 1.8 and 2.5 eV. The effect of degradation induced by light exposure for several hours was studied using Photothermal Deflexion Spectroscopy (PDS). The experimental data are consistent with a bond breaking model, by conversion of tail weak bonds into dangling bonds. The data show more stability in the optoelectronic properties of diluted samples.

Structural and electrical characterization of the 4H-SiC based junction field effect transistor (JFET)

The main focus of our work is the characterization and structural study of 4H-silicon carbide (SiC) normally-off vertical junction field effect transistor (JFET). We will determine the experimental static Ids-Vds characteristics under temperature variation. In order to achieve a better description of SiC and metal interface properties, many interesting parameters related to the material and to the device performance have been obtained from these measurements. Simulation has been used to correlate obtained results to physical parameters. When the temperature increases to 300°C, the RDS(ON) increase to 700 MΩ and the saturation drain source current decreases up to 14A.