AVS 60th International Symposium and Exhibition
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM7
Gallium Nitride Surface Preparation for ALD Deposition of Aluminum Oxide

Friday, November 1, 2013, 10:20 am, Room 201 A

Session: Oxides and Semiconductors: Structure and Reactivity
Presenter: A.J. Kerr, University of California, San Diego
Authors: A.J. Kerr, University of California, San Diego
S. Gu, University of California, San Diego
T. Kaufman-Osborn, University of California, San Diego
E. Chagarov, University of California, San Diego
S. Madisetti, University at Albany-SUNY
P. Asbeck, University of California, San Diego
S. Oktyabrsky, University at Albany-SUNY
A.C. Kummel, University of California, San Diego
Correspondent: Click to Email
Gallium nitride metal oxide semiconductor field-effect transistors (MOSFET) are promising candidates for high-speed and high-power circuits due to their voltage handling capability and high electron mobility. For these devices to function optimally, the oxide-semiconductor interface must have a low density of interfacial traps which can degrade performance and reliability. This study correlates the electrical properties and chemical bonding of deposited amorphous Al2O3 on GaN(0001) prepared using ammonium sulfide solutions followed by in-situ atomic hydrogen cleaning.

A baseline CV measurement was made using simple TMA predosing in the ALD system to reduce native oxide (Fig 1a). The ex-situ sulfide solution cleaning prior to cyclic atomic H and TMA predosing resulted in improved C-V characteristics illustrated by decreased dispersion across the frequency spectrum. The greatest improvement in dispersion, however, was achieved when combining the ex-situ wet sulfur treatment with in-situ when atomic hydrogen plasma cleaning (Fig 1b.). To understand the role of the ex-situ wet sulfur treatment and in-situ atomic H cleaning, XPS, LEED, and SIMS were performed. Following wet sulfur treatment, in-situ XPS and LEED studies showed that heating to typical ALD temperatures (285°C) both removed the sulfur and produces a 1x1 LEED pattern consistent with less than a monolayer of disorder at the surface. SIM experiments upon the full oxide/GaN structures confirmed minimal sulfur at the buried oxide-semiconductor interface consistent with the main role of sulfur being to protect the surface against oxidation in air instead of providing a chemical passivation at the oxide/semiconductor interface. Angle resolved XPS studies of the ALD nucleation layers showed the primary role of the in-situ atomic hydrogen was to increase the initial growth rate of the gate oxide thereby increasing the ALD nucleation density consistent with previous reports demonstrating that atomic hydrogen completely removes native oxide. Density Functional Theory Molecular Dynamics (DFTMD) calculations(Fig. 2 and 3) were performed to compare the bonding of the amorphous Al2O3 gate oxide to a bulk terminated GaN(0001) versus a GaN(0001) surface with a Ga adlayer. The bonding of the amorphous Al2O3 gate oxide directly to the bulk terminated GaN(0001) was most consistent with the experimental results since this interface had bulk-like charge states for the interfacial atoms and a very low density of band gap states compared to even the clean GaN(0001) surface.