Abstract
We explore the electronic and photonic properties of two-dimensional (2D) materials including GaAs/AlGaAs heterostructure, graphene, and graphene-GaAs/AlGaAs composite material. Novel 2D materials have allowed us to study a plenty of physics phenomena and to develop versatile hybrid devices. GaAs/AlGaAs heterostructure with massive 2D electron gas (2DEG) embedded in the interface exhibits a parabolic energy dispersion and yields high carrier mobility. Graphene, a single sheet of carbon atoms arranged in a honeycomb lattice, is a natural 2D material with a linear low-energy dispersion, displaying massless Dirac fermions. This thesis elucidates the integration of graphene to conventional III-V semiconductor heterostructure as a novel bilayer 2D system. We investigate three types of devices with different functionalities to study the unique properties of this system and to demonstrate its potential applications. First, we present the realization of a dual-function field-effect transistor (DFET), consisting of a graphene FET (GFET) and a high electron mobility transistor (HEMT). Depending on the operation scheme, graphene can be used either as a gate electrode for HMET or as a channel material gated by 2DEG formed in the interface of heterojunction. The performance of GFET is limited by the interface band bending of the heterojunction associated with the gating voltages and the intrinsic surface morphology of GaAs substrate. The performance of this hybrid device is demonstrated to be comparable with that of GFET or HMET reported earlier, which bodes a way for the development of integrated bi-FET device for further applications and physical investigations. Second, we develop a quantum Hall far-infrared (QHFIR) photon detector based on graphene-GaAs/AlGaAs composite material. Graphene is employed as a transparent top-gate electrode to tune the response (cyclotron) frequency of the QHFIR. As covered with graphene, the photoresponse of the QHFIR detector is found enhanced. The enhancement in the photosignal is referred to the built-up electric field in between graphene and 2DEG. Third, we implement a sensitive micron-sized Hall probe on large-scale graphene for magnetic imaging at room temperature. Conventional Hall probe based on GaAs 2DEG suffers restricted spatial resolution due to a finite spacer layer. Graphene Hall probe (GHP) can overcome this issue and supposedly provide superior field sensitivity in the vicinity of charge neutral regime. Our studies indicate that the fundamental limitation of the field sensitivity and resolution are respectively restricted by extrinsic and intrinsic defects. Our result paves a way for the use of CVD GHPs for scanning Hall probe microscopy with high field sensitivity. We also suggest a scheme based on a stacked double-Hall junction in a graphene-GaAs/AlGaAs composite material to further extend the functionalities of Hall probes. Fourth, we construct a scanning Hall probe microscope (SHPM) for micron- magnetic profile imaging. The SHPM combines (sub) micron-sized spatial resolution, a large scanning range, and a wide range of operating temperatures (4.2 to 300 K). The unique designs of the SHPM system includes a simple positioning (sub)-micron XY stage, a direct contact scheme without a sophisticated feedback control system for the Z-axis, and a innovative lithography process to fabricate the scanning Hall probe. Detailed experimental procedures of fabricating a scanning Hall probe are given. To demonstrate the capabilities of this system, we present magnetic images of the nickel grid pattern at room temperature, of the surface magnetic domain structure of a La_(2/3)Ca_(1/3)MnO_3 thin film at 77 K, and of the superconducting vortex patterns on striped niobium film at 4.2 K. Last, we present detailed experimental procedures of preparing chemical-vapor deposited graphene. A hydrochloric acid assisted clean to the copper foil before graphene growth is demonstrated very effective in reducing contaminants gathered on the graphene surface. Summaries of the basic properties of CVD graphene and GaAs/AlGaAs and device fabrication procedures are also given.