AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Monday Sessions
       Session EM+TF-MoM

Paper EM+TF-MoM11
Density Function Theory Simulations of a-Al2O3/GaN(0001) Interfaces Resulting from Ex Situ and In Situ Surface Preparation

Monday, October 28, 2013, 11:40 am, Room 101 B

Session: High-k Gate Oxides for High Mobility Semiconductors I
Presenter: A.C. Kummel, University of California San Diego
Authors: A.C. Kummel, University of California San Diego
E. Chagarov, University of California San Diego
S. Gu, University of California San Diego
P. Asbeck, University of California San Diego
S. Madisetti, University at Albany-SUNY
S. Oktyabrsky, University at Albany-SUNY
T. Kaufman-Osborn, University of California San Diego
A.J. Kerr, University of California San Diego
Correspondent: Click to Email
The structural and electronic properties of amorphous a-Al2O3/GaN(0001) interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic amorphous a-Al2O3 samples were generated using a hybrid classical-DFT MD “melt-and-quench” approach and tested against experimental properties. Every stack was annealed at 800K, cooled to 0K and relaxed to the ground state giving the system enough freedom to form realistic interface. The simulated stacks were recalculated with HSE 06 hybrid-functional to provide accurate electronic structure analysis and bandgap representation. Subsequently, a series of a-Al2O3/GaN(0001) interfaces were investigated by bonding the oxide to various GaN(0001) surfaces and annealing the stacks at 800K for 2000 time steps, cooling to 0K and relaxing to form the final structures. GaN(0001) (Ga-polar) models where chosen to simulate the surfaces obtained with different ex-situ wet cleaning and in-situ dry cleaning including NH4OH(aq), O2(g) oxidation, (NH4­)2S, NH3(plasma), and TMA /H(plasma treatments). Nearly all MBE GaN(0001) surfaces are prepared with a Ga adlayer. The inclusion of Ga-adlayer resulted in an a-Al2O3/GaN(0001) bonding with multiple midgap states mainly from metal-metal (Al-Ga) bonds. In-situ O2 reaction at 500˚C has been previous shown to eliminate metal-metal bonding within the Ga-adlayer/GaN(0001); DFT-MD simulations show that the resultant O-Ga-O layer provides an excellent passivation layer between a-Al2O3 and GaN. The DFT-MD simulations of direct bonding between a-Al2O3 and GaN(0001) revealed predominantly Ga-O bonding with no intermixing; the simulations show the key to forming a passive interface is nucleating the ALD in each unit cells to remove all Ga dangling bond states. A 5-step combined ex-situ wet cleaning and in-situ cyclic TMA /H treatment resulted in an extremely high nucleation density and concurrent lower dispersion in both threshold and accumulation capacitance consistent with lower interfacial defect density and lower border trap density. XPS experiments showed the bonding at the interface was covalent consistent with the DFT calculations.