AVS 53rd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuM

Paper EM-TuM1
Impact of Subsurface Defects in Metal-ZnO(000-1) Schottky Barrier Formation

Tuesday, November 14, 2006, 8:00 am, Room 2003

Session: Zinc Oxide
Presenter: H.L. Mosbacker, The Ohio State University
Authors: H.L. Mosbacker, The Ohio State University
M.J. Hetzer, The Ohio State University
Y.M. Strzhemechny, Texas Christian University
M. Gonzalez, The Ohio State University
S.A. Ringel, The Ohio State University
D.C. Look, Wright State University
G. Cantwell, ZN Technology, Inc.
L.J. Brillson, The Ohio State University
Correspondent: Click to Email
ZnO has emerged as a leading candidate for next generation semiconductor electronics due to its superior optoelectronic, microelectronic, and nanoelectronic properties. Central to realizing ZnO device applications are their electrical contacts with metals, yet Schottky barrier studies over the past 4 decades have not taken a comprehensive approach to isolating effects due to surface contamination, lattice defects, impurity dopants, and interface chemical reactions. We have used low energy depth-resolved cathodoluminescence spectroscopy (DRCLS) at 10 K in an ultrahigh vacuum scanning electron microscope and macroscopic current-voltage (I-V) measurements to study Schottky barrier (SB) formation at metal interfaces to clean, ordered ZnO(000-1). We fabricated sets of 30 nm-thick, 0.4 mm diameter Au, Al, Ni, Pt, Pd, Mo, Ta and Ir diodes on the same single crystal surfaces from different vendors. Prior to metallization, DRCLS revealed orders-of-magnitude difference in native bulk defect densities for crystals grown by different techniques, and these defect densities varied substantially between the crystals' bulk and surface. For all crystals, surfaces treated with a remote oxygen (20% O2/80% He) plasma created clean, ordered surfaces and reduced defect emissions in the surface region. Micro-DRCLS taken through the metal diodes revealed defect transitions at 2.1,2.5, and 3.0 eV that change dramatically with process steps and metal. I-V measurements exhibited transitions from Ohmic to SBs and lower idealities for Pt, Au, Ir, and Pd with plasma treatment. Deep-level optical and transient spectroscopies correlated bulk and surface defects, showing deep levels at 2.54 eV and 0.53 eV, while DRCLS shows that these densities can increase by > 100x at the surface. Our results indicate that metals can induce defects at the ZnO surface and impact device performance. The magnitude of the metal's influence directly correlates to the defect densities at the surface and ZnO bulk.