Studies of metal contacts on (11(2-bar)0) zinc oxide and magnesium zinc oxide films

Metal-semiconductor contacts play a key role in realizing high performance of electronic devices. This dissertation addresses the comprehensive studies and development of ohmic and Schottky contacts to ZnO and MgxZn 1-xO films, and their applications in UV photodetectors.; (11 2¯ 0) ZnO and MgxZn1-xO films (x ≤ 0.33) have been epitaxially grown on R-Al2O3 substrates using metal organic chemical vapor deposition (MOCVD). Nonalloyed Al ohmic contacts have been achieved to ZnO and MgxZn1-xO films. For Al-ZnO (n ∼ 1.6 x 1017 cm-3 ) contacts, a specific contact resistance as low as 2.5 x 10 -5 O cm2 is obtained. Thermionic field emission is found to be the predominary current transport mechanism. For Al-Mg xZn1-xO contacts, it is found that HCl etching before Al metallization reduces the specific contact resistances by one order of magnitude. Ta is selected as a new metal scheme to form alloyed ohmic contacts to ZnO due to its low work function. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) are used to study the contact formation mechanism. SEM is used to monitor the surface morphology change during the contact formation. After optimizing the annealing condition, a specific contact resistance of 5.4 x 10-6 O cm2 is achieved.; The Schottky diode on epitaxial (11 2¯ 0) ZnO films is demonstrated using Al and Ag as the ohmic and Schottky contact metals, respectively. For (11 2¯ 0) ZnO, the c-axis of ZnO lies in the film surface, where the cations (Zn) and anions (O) are in the stoichiometric ratio. This results in zero net charge on the surface, and zero dipole moment perpendicular to the growth plane. This unique non-polar orientation is beneficial to form stable Schottky contacts. The ideality factor of the Ag-ZnO Schottky diode is found to be ∼1.33. The flat band model is adopted to determine the flat band barrier height, which is ∼0.89 eV. For Ag-Mg0.18Zn 0.82O Schottky diode, an ideality factor of 1.31 is obtained and the flat band barrier height is calculated to be ∼0.95 eV. The metal-semiconductor-metal (MSM) Schottky type UV detectors on epitaxial (11 2¯ 0) ZnO films are fabricated. The detectors show a rise time of ∼20 ns and a fall time of ∼50 ns, unprecedentedly faster than the previously reported results in the literature. Ag-MgxZn1-xO Schottky type photodetectors show the cutoff wavelengths' shift to the shorter wavelength range as the Mg composition increases, promising for UV applications.