FABRICATION and CHARACTERIZATION of BIDIMENSIONAL ELECTRONIC GAS (2DEG) in ZnO BASED HETEROSTRUCTURES

Spintronics and High Electronic Mobility Transistors (HEMTs) are active frontiers in the development of electronic devices. For their development, Diluted Magnetic Semiconductors (DMS) and heterostructures hosting Two Dimensional Electronic Gas (2DEG) are required. MBE has become into the state of the art technique to prepare ZnO based heterostructures, surpassing PLD limitations. However, the former has a much more complex operation and higher costs. In order to improve the quality of ZnO based heterostructures at bounded costs, a low oxidative MBE process was studied. The aim of the present thesis is double: first, it intends to make a contribution to the knowledge of the non conventional low oxidative MBE production of ZnO heterostructures. In particular we wanted to assess its feasibility and understand the growth mechanism. Second, this thesis intends to make specific contributions to the physics of electric transport in such heterostructures, namely Electric Field modulated Magnetoresistance and 2DEG Magnetic Field Effective Mass Enhancement. For the first objective, 142 MgO/ZnO heterostructures were grown on sapphire on a home-made MBE in low oxidative conditions. An extensive characterization of the sample set by RHEED, AFM, XRD, SEM, EDS and Transport measurement was carried out. The analysis of the data gathered made it possible to identify different growth stages of the ZnO structures. They were mainly discussed in terms of misfit accommodation. The results suggest a complex process with interlinked steps, in which subtle transformations take place. For the second objective, Field Effect devices were produced by depositing Co:ZnO/STO heterostructures by PLD. After XRD, AFM, TEM and magnetic characterization, transport measurements were carried out. The magnetic scattering was studied by appropriate model fitting and discussed in terms of percolation of Bounded Magnetic Polarons (BMP). The results suggest free charge carrier mediated magnetic polarization of Co:ZnO. Next, a 2DEG hosting Mg:ZnO/ZnO heterostructure was deposited by PLD. Transport measurements showed complex quantum oscillations. The simultaneous model fitting for all temperatures showed magnetic field effective mass enhancement. The results suggest band non-parabolicity and electron-electron correlation as possible causes.