Interface Trap Characterization of ALD-grown Al₂O₃/GaN MIS Capacitors

The use of Al₂O₃ deposited by atomic layer deposition (ALD) in GaN-based transistors may improve device performance, by reducing gate leakage and passivating surface states, and is receiving great interest. However, little work has been done to characterize interface states and bulk dielectric defects in such structures. The presence, concentration and distribution of defects likely depend on interface nucleation and the ALD process. Thus, process optimization will require identifying traps and fixed charges, determining location within the layers and improving fabrication to decrease trap and fixed charge densities. This work centers on characterizing traps at the interface between GaN and ALD-grown Al₂O₃. Interface defect characterization is performed by constant capacitance deep level transient spectroscopy (CC-DLTS) in tandem with constant capacitance deep level optical spectroscopy (CC-DLOS), making it possible to probe the interface over the entire GaN bandgap. To investigate the role of Al₂O₃ thickness on interface state densities and explore the presence of Al₂O₃ bulk traps, 6.8, 13.4, and 19.8nm thick films of ALD Al₂O₃ were deposited on NH₃-MBE n-type Ga-polar GaN substrates. The as-deposited Al₂O₃ films were fabricated into MIS capacitors using e-beam evaporated semitransparent Ni contacts on the Al₂O₃ and Ti/Al/Ni/Au Ohmic contacts to the GaN. Additionally, Ni/GaN Schottky diodes were fabricated on the substrate to separately determine bulk traps in the GaN.Using CC-DLTS/DLOS, the interface trap densities, D_it, of the three films were determined to be nearly identical, independent of Al₂O₃ thickness. Such agreement suggests that the concentration of traps within the oxide is small compared to the density of traps at the interface. Bulk GaN traps are accounted for in the analysis of the MIS spectroscopy signals. The Al₂O₃/GaN D_it spectra had a U-shape with D_it ~10¹²cm^-2eV^-1 near the conduction band edge, ~10¹¹cm^-2eV^-1 mid-gap, and ~10¹⁴cm^-2eV^-1 near the valence band edge. The 6.8nm and 13.4nm Al₂O₃ samples showed a factor of four and a factor of two increase in D_it near the conduction band edge, respectively, compared with the 19.8nm Al₂O₃ sample. The inverse relationship with thickness indicates this increase cannot be due to bulk Al₂O₃ traps and indicates that the interface is slightly improved with increased film thickness. These films were not annealed, so the increased time at 300°C during the deposition may lead to slight reduction in D_it.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Electrical and Computer Engineering

Grantor dc:publisher

The Ohio State University

Year dc:date

2013

Author dc:creator

• Jackson, Christine M.

Contributors dc:contributor

• Ringel, Steven

• Electrical Engineering

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=osu1366229216

OAI identifier oai:identifier

oai:etd.ohiolink.edu:osu1366229216