Some experimental studies of n-type GaN and Au/GaN contacts" by Ke, Wang, 王科, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author.
Abstract:

Abstract of thesis entitled SOME EXPERIMENTAL STUDIES OF N-TYPE GaN AND Au/GaN CONTACTS Submitted by Wang Ke for the degree of Master of Philosophy at The University of Hong Kong in December 2002

Schottky and ohmic contacts made on both undoped n-type HVPE (Hydride Vapour Phase Epitaxy) and MBE (Molecular Beam Epitaxy) grown GaN epilayers with similar nominal carrier-concentration levels were studied. Close to ideal Au- GaN Schottky junctions together with low resistance Al and In ohmic contacts were obtained when using the HVPE material. For the MBE material, however, under identical fabrication procedures the electrical characteristics of both Schottky and ohmic contacts were poor. The result was correlated with the material quality of the epilayers observed by photoluminescence spectroscopy, Hall measurement and atomic-force microscopy, which showed that the concentrations of point defects and dislocations were significantly higher in the MBE grown material. It is suggested that point defects or impurity-related defects lead to Schottky contact degradation and the observed increase in ohmic contact resistance. These results show the importance of material quality when making contacts on GaN epilayers and suggest that the intensity of the band-to-band photoluminescence signal is a suitable parameter for assessing the material quality prior to metalization. The electrical characteristics of Au/n-GaN Schottky contacts with different Au film thickness up to 1300A were investigated using current-voltage (I-V) and capacitance-voltage (C-V) techniques. The results showed a steady decrease in the quality of the Schottky diodes for increasing Au-film thickness. The I-V measurements indicated that thin (500 A). Schottky barrier heights obtained by C-V analysis were 0.1-0.2eV greater than those found from the I-V measurements, indicating that current transport through the barrier is not purely thermionic. Ideality factors of 2 confirmed this. Both Schottky barrier height and reverse breakdown bias were found to decrease with increasing Au thickness. Depth profiling Auger Electron Spectroscopy (AES) showed that the Au/GaN junction interface width increased with increasing Au thickness, and suggesting considerable inter-mixing of Au, Ga and N. The results were interpreted in terms of Ga out-diffusion from the GaN giving rise to gallium vacancies that in turn acted as sites for electron-hole pair generation within the depletion region. The study supports the recent suggestion that gallium vacancies associated with threaded dislocations play an important role in junction breakdown.
DOI: 10.5353/th_b2666361
Subjects:
Gallium nitride
Ohmic contacts
Diodes, Schottky-barrier

Some Experimental Studies of N-Type Gan and Au/Gan Contacts