Effects of SiO: nano layers on the performance of CdBr:/Ga:S3 heterojunctions. رسالة ماجستير

Abstract

In this thesis, we focused on studying the effect of SiO2 nano layer on the structural, morphological, optical and electrical properties of CdBr2/Ga2S3 heterojunctions. The heterojunctions were fabricated by the thermal evaporation techniques under a vapor pressure of 10° mbar. The structural, optical and electrical properties were carried out by means of X-ray diffraction techniques, ultraviolent-visible light spectrophotometry in the range of 300-1100 nm and impedance spectroscopy techniques, respectively. In this issue, the films are observed to exhibit a hexagonal structure. In addition, the lattice parameters, the microstrain, the dislocation densities and stacking faults were determined and discussed. The optical spectrophotometry measurements and analysis on the heterojunction devices revealed that the coating of Ga2S3 onto the surface of CdBr/SiO2 causes a reduction in the band gap to 3.55 eV and forces a deformation in the hexagonal structure of CdBrz/SiO2. The energy band diagram for CdBr:/SiO2/Ga2S3 exposed a conduction band offsets of values of 0.97 and 2.35 eV at the CdBr2/SiO: and SiO2 /GaaS3 interfaces, respectively, while the valence band offsets are 4.42 and 3.17 at the CdBr/SiO2 and SiOz /Ga2S3 interfaces, respectively. In addition, the dielectric dispersion analysis on the samples have shown that the insertion of SiO2 nano-slabs enhances the dielectric response near 1.89 eV. The modeling of the optical conductivity of the stacked layers which was carried out with the help of Drude-Lorentz approach allowed determing the optical conductivity parameters. These parameters include the scattering time at femto-second level, the oscillator energy, the free carrier density, the plasmon frequency and the drift mobility. In the presence of SiO2, the drift mobility reached 293 cm/Vs. Furthermore, the impedance spectroscopy analysis in the

frequency domain of 10-1800 MHz have shown that the proposed device can excited negative capacitance effect accompanied with resonance-antiresonance phenomena. The strange behavior of capacitance which is modeled in accordance with Qasrawi- Ershov model indicated that the exchange between the interface charges is the main reason beyond the negative capacitance effect. Modeling of the electrical conductivity have shown that the electrical conduction is dominated by quantum mechanical tunneling and by the correlated barrier hopping conduction. The features of the CdBr/Ga2S3 device in the presence of SiO2 make them attractive for use as optical

reactive and microwave resonators.