| AVS 58th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing Division | Tuesday Sessions |
| Session EM+TF-TuM |
| Session: | High-k Dielectrics for MOSFETs Part 1 |
| Presenter: | Ting-Hsiang Hung, Ohio State University |
| Authors: | M. Esposto, Ohio State University S. Krishnamoorthy, Ohio State University D.N. Nath, Ohio State University S. Bajaj, Ohio State University S. Rajan, Ohio State University T.-H. Hung, Ohio State University |
| Correspondent: | Click to Email |
We report on the deposition and energy band diagram analysis of high-quality low-leakage Al2O3/GaN using atomic layer deposition. As GaN-based transistors are scaled to achieve higher frequency operation, atomic layer deposition techniques offer a promising way to achieve low leakage while scaling gate-to-channel distance. In addition, applications of GaN in power switching systems require ultra-low leakage that can be achieved using metal-insulator-semiconductor (MISHEMT) structures. In this work, we have made quantitative estimates of conduction band offsets and interface charge density.
MIS structures with varying oxide thickness were fabricated on an n+/n- GaN sample grown by RF plasma MBE on low dislocation density Lumilog GaN templates. Three Al2O3 layers of nominal 6 nm, 12 nm, and 18 nm were deposited by atomic layer deposition at 300˚C, using trimethylaluminum (TMA) and H2O as precursors. The pre-deposition treatment of the surface consisted in a 10:1 HF-dip for 15s. All three samples were then annealed at 600˚C in forming gas for 1min. A new ALD deposition procedure was also developed to achieve low leakage in these structures.
A quantitative analysis of the interface barrier of Ni/Al2O3/GaN capacitors was carried out to determine conduction band discontinuity, interface fixed charge and pinning effects. The I-V measurements show extremely low current density for thin dielectric films. A quantitative energy band diagram was estimated from capacitance voltage (C-V) measurements by extracting the apparent charge profiles of the MIS capacitors taking into account the spontaneous polarization in GaN and doping. The extracted flat-band voltages were -0.36 V, -1.55 V and -2.73 V for the 6 nm, 12 nm and 18 nm-thick oxide respectively. The hysteresis in the C-V profile for the 6nm-thick capacitor pointed out a Dit charge density of approximately 5x1011 cm-2 and higher for the thicker capacitors. This was because the deposition and post deposition annealing conditions were optimized for very thin oxide layers (~ 5-6 nm). A linear relationship between the flat-band voltage and the oxide thickness was experimentally observed, indicating absence of Fermi-level pinning at the Al2O3/GaN interface. The conduction band offset at the Al2O3/GaN interface was calculated to be 2.66 eV. In addition, we estimate that a non-zero field of approximately 2 MV/cm exists in the oxide under flat band conditions in the semiconductor. This non-zero field is attributed to a fixed charge density at the Al2O3/GaN interface of 2.79x1013 cm-2.