Design and Characterization of WO3/Ga:S3 heterojunctions رسالة ماجستير

Abstract

In this thesis, we report the design and characterizations of WO3/GazS3 heterojunction hybrid devices. The devices which are grown by the physical evaporation technique under vacuum pressure of 10% mbar are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM(, energy dispersive X-ray spectroscopy )EDX), UV-VIS spectrophotometry, impedance spectroscopy, capacitance-voltage and current-voltage characteristics curves. While the X-ray diffraction indicated amorphous nature of the grown materials, the SEM images displayed no particular morphology confirming the amorphous nature of growth. The EDX analysis displays stechiometric composition of the grown materials. Optically, while WO3 and GaaS3 exhibit energy band gap values of 3.17 and 2.53 eV, respectively, the WO3/GaaS interface exhibit an energy band gap of 2.62 eV and resulted in an aligned conduction band with valence band offset of 0.61 eV. The optically interfaced layers exhibit deep band tail of width of 0.78 eV. In addition, the electrical measurements has shown that the device which is coated onto Yb substrate and recoated with Au pad exhibit capacitance-voltage characteristics that nominate it for use a s MOSFET devices. The current-voltage characteristics also displayed rectifying features within a barrier height of 0.73 eV under forward bias conditions. The reduction of series resistance effect indicated ideal diode characteristics. On the other hand, the impedance spectroscopy analysis had shown that the device can exhibit wide capacitance and impedance tunability in the frequency domain of 10-1800 MHz nominating it as tunable capacitors. It was also observed that the Yb/WO3/GazS3/Au hybrid devices exhibit band stop features with notch

frequency of 1.65 GHz. The test of the return loss values of the propagating ac signal displayed high quality signal and good impedance match nominating the device for applications as band

stop filters.