Engineering of the Optical, Structural, Electrical, and Magnetic Properties of Oxides and Nitrides of In-Ga-Zn Thin Films Using Nanotechnology

The various thin film systems studied in this dissertation are outlined in Chapter one. Two groups of nitride and oxide thin film semiconductors were studied. The nitride group includes c-In_xGa_1-xN (x = 12, 19, and 55%), c-(In_0.06Ga_0.94N/GaN)-SLs, and a-In_0.74B_0.26N. The oxide group includes a-In_0.06Ga_0.47Zn_0.03O_0.45 and various compositions of a-In_xGa_yZn_zO_β alloys. All films were grown using reactive magnetron sputtering except c-(In_0.06Ga_0.94N/GaN)-SLs, which were grown using metal {organic chemical vapor deposition (MOCVD).

For c-In_xGa_1-xaN thin films, two crystallographic orientations are observed, (0002) and (101̅1). The optical bandgap decreases with increasing In at.%. In addition, we characterize the electrical properties using Hall effect measurements,and relate them to the structure and composition. c-(In_0.06Ga_0.94N/GaN)-SLs are studied by X-ray diffraction. Simulation for the as-deposited SL was achieved in the frame work of fully strained SL structure. It was found that implantation with Eu3+ ions causes partial degradation of the SL structure, which can be highly recovered by annealing at high temperatures. For a-In0.74B0.26N thin films, we mainly characterize the optical properties using spectroscopic ellipsometry (SE). The measured SE spectra are described very well by a two-layer model structure, which consists of a transparent layer on top of an absorbing layer. We believe that oxidizing the upper layer is caused by formed voids due to alloying with boron, that creates paths for oxygen to diffuse into the upper layer and oxidize it.

The optical and magnetic properties of a-In_0.06Ga_0.47Zn_0.03O_0.45 thin films were studied in depth. The bandgap determined by various methods has an average value of 3.85 eV, and the re ectivity shows that a-In_0.06Ga_0.47Zn_0.03O_0.45 could be a good candidate for anti-reflective coating. We prove that some or all of the indium, gallium, and oxygen ions exist in mixed oxidation states, which manifest an induced FM interaction. We then engineer the optical bandgap and optical functions for various compositions of a-In_xGa_yZn_zO_β with relatively small In at.%. By changing the composition at.%, we were able to switch the FM interaction on and off, which is caused by switching the oxidations states of ions between mixed and pure states.