Master of Science (MS), Wright State University, 2007, Physics

Mitchell, William D. M.S., Department of Physics, Wright State University, 2007. Polarization reversal in both hydrothermal and flux grown potassium titanyl phosphate was studied using square pulses at room temperature from 1600 V/mm to 5000 V/mm. Maximum switching current and inverse switching time data is compared to the ferroelectric polarization reversal model developed by Fatuzzo and Merz in the last century. Room temperature calculation of spontaneous polarization is reported and compared to that of potassium titanyl phosphate in the literature.

Committee: Lok Lew Yan Voon (Advisor) Subjects: Physics, Condensed Matter

Doctor of Philosophy, The Ohio State University, 2006, Physics

The electronic properties of stacking-fault (SF) induced inclusions in hexagonal silicon carbide (SiC) and the valence band structure of 3C- and 4H-SiC are studied using ultrahigh vacuum ballistic electron/hole emission microscopy (BEEM/BHEM). Our contribution to the denuded-zone formation in Si epitaxy on Si(001) is also presented. In recent years, the SF inclusions with local 3C or 8H stacking sequence have been found to form in 4H- or 6H-SiC in various circumstances, which can be of concern in terms of device performance and reliability. We show that both 3C and 8H inclusions behave as electron quantum wells (QWs) by measuring local Schottky barrier heights (SBHs) on and away from inclusions with BEEM. The QW energy level of single SF 3C inclusions formed during 4H-SiC p-i-n diode operation is measured to be ~0.25 eV below the conduction band minimum (CBM) of 4H-SiC. In comparison, a deeper QW energy depth (~0.53 eV) was previously measured on double SF 3C inclusions formed in 4H-SiC during high-temperature processing. From the capacitance-voltage (C-V) measurements and electrostatic modeling on the 2SF sample, we show that free carrier charging of the inclusions in the bulk can reduce the C-V extracted SBH. The QW energy depth of the 8H inclusions formed during 4H-SiC epilayer growth is measured to be ~0.39 eV below 4H-SiC CBM. In addition, we observe the direct effect of the spontaneous polarization difference between 8H- and 4H-SiC on local SBH, as well as the strong reflection of injected hot electrons from subsurface 8H inclusions. The valence band maximum (VBM) of 3C-SiC is estimated to be ~0.06 eV lower than 4H-SiC using BHEM. No evidence of additional VBM in 3C-SiC supports that the second VBM observed in 4H-SiC is a crystal-field split VBM located ~110 meV below the highest VBM. Our earlier study of the denuded-zone formation in Si epitaxy on Si(001) is also described. Both Monte Carlo simulation (small critical cluster) and the continuum model (large cr (open full item for complete abstract)

Committee: Jonathan Pelz (Advisor) Subjects: Physics, Condensed Matter