|Title:||Transport and optical characteristics of graphene-based hybrid structure and two-dimensional layered gallium selenide|
|Advisors:||Hao, Jianhua (AP)|
Graphene -- Electric properties.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Applied Physics|
|Pages:||xxi, 161 leaves : illustrations ; 30 cm|
|Abstract:||Due to its unique two-dimensional (2D) structure and fascinating properties, graphene has revealed potential applications in many aspects since it was first discovered by a micro-mechanical exfoliation method. Beyond graphene, a big family of 2D materials has been discovered subsequently. Their potential has been developed from basic electronic and optoelectronic devices to a wide range of applications. Among them, 2D GaSe, as a recently discovered 2D material, has received lifted attention and been studied extensively in the matter of fabrication techniques and potential applications. Therefore, it is important to investigate the fundamental properties of these 2D materials for further understanding and future applications of them. In this thesis, firstly, a non-volatile memory can be fabricated by integrating graphene with ferroelectric [Pb(Mg₁/₃Nb₂/₃)O₃]-[PbTiO₃] (PMN-PT) based on a field effect transistor (FET) structure. The fabricated FET exhibited p-type characteristics with a large memory window. By pre-poling the PMN-PT substrate, a reduction in p-doping of the FET can be achieved. On the other hand, it should be noted the fact that ferroelectric materials are capable of producing controllable biaxial strain due to the piezoelectric effects. Such tunable strain can result in a blue shift in 2D band of graphene. And more interesting, a continuous 2D band shift can be detected during the retention of a bias voltage. Secondly, graphene/Si Schottky junction solar cells have drawn much attention and been investigated extensively due to their potential applications. In comparison with Si, GaAs has the merits of high electron mobility and direct band gap. Herein, n-type GaAs has been integrated with graphene sheets to fabricate Schottky junction solar cells. The Schottky junction shows photovoltaic behaviors with a power conversion efficiency of 1.95 %. Thirdly, nonlinear optics in GaSe bulk crystals has been studied for decades, such property in its 2D counterpart is unknown and of much significance. We report a strong layer- and power-dependent second harmonic generation (SHG) at few-layer GaSe sheets. Two-photon excited fluorescence has also been observed in GaSe nanosheets. Our free energy calculations on GaSe bulk and layers based on first-principles methods support the observed nonlinear optical phenomena in the atomically thin layers. In conclutions, the electronic and optoelectric characteristics of graphene have been investigated by integrating graphene with functional materials of ferroelectric and semeconductor, followed by a study of the nonlinear optical properties of 2D GaSe flakes. These fundamental studies will aid further research of 2D materials and show promise for their future applications in nanoelectronics and nanophotonics.|
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