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Degree

Doctor of Philosophy, Ohio State University, Physics, 2001.

Abstract

Ultrahigh vacuum (UHV) ballistic electron emission microscopy (BEEM) is used to study at nanometer scale the phenomena associated with the Schottky barrier inhomogeneity and defect-related charge of silicon carbide (SiC) and gallium nitride (GaN). Also some results of studies of effects of UHV premetallization annealing and hydrogen exposure on Pd/SiC Schottky contacts, as well as our contribution to a study of boron segregation in annealed B-doped Si using Auger electron spectroscopy (AES) are presented. We show that BEEM can be used to probe nanometer scale spatial inhomogeneity of Schottky barrier height (SBH) and to extract information about conduction band structures of different polytypes (6H, 4H, and 15R) of SiC. We have performed the first successful BEEM measurements on SiC, from which SBHs and the energy separations of the second conduction band minima (CBM) of 4H- and 15R-SiC were extracted. Direct observation of the image force lowering of SiC Schottky barrier are presented as well. Also we used BEEM to characterize individual threading dislocations (TDs) in GaN crystals grown on sapphire substrates. Potential barrier profiles and ballistic transmittance across GaN Schottky contacts were measured across individual TDs, which subsequently were used to set a limit on possible trapped negative charges along the dislocations. In contrast to several prior studies, we find no indication of near-interface fixed negative dislocation charge at specific TD structures. We have performed a detailed study of diode nonidealities on the fabricated SiC Schottky contacts, such as large excess leakage current and deviation from thermionic emission theory. Tung and others had shown that a range of “nonideal” behaviors of Schottky diodes could be quantitatively explained by assuming a distribution of nanometer-sized interfacial “patches” of reduced SBH undergoing potential pinch-off. We extended this proposed model to calculate the microscopic barrier height distribution (BHD) for the assumed patch distributions. Our measurements indicate that the large excess current in highly nonideal diodes is most likely due to a few large defects of extrinsic origin, which were not considered in the original model. This last conclusion is consistent with a recent electron beam induced current (EBIC) study by Skromme and co-workers.

Keywords

BEEM; diode; Schottky; SBH; STM/BEEM; BHD; Pd/SiC

Advisor

Jonathan Pelz

Document number: osu1000844302
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=osu1000844302

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