1. Properties of HfO 2 Deposited on AlGaN/GaN Structures Using e-beam Technique V. Tokranov a, S. Oktyabrsky a, S.L. Rumyantsev b, M.S. Shur b, N. Pala b,c, R. Jain c, J. Yang c and R. Gaska c,* a) Coll. of Nanoscale Sci. & Eng., Univ. at Albany-SUNY, NY b) Rensselaer Polytechnic Institute, Troy NY 12180-3590 c) Sensor Electronic Technology, Inc. 1195 Atlas Road Columbia, SC 29209 *Corresponding author: gaska@s-et.com Motivation GaN/AlGaN HEMTs suffer from poor long-term stability and the gate leakage current of the Schottky gate devices. Gate leakage increases the sub threshold current and shunts the gate to channel capacitance, which decrease the maximum output power. Insulated gate devices have reduced leakage current and can operate at positive gate voltage, yielding higher saturation current and higher output RF power. However, current gate insulation techniques cause decrease of the device transconductance and increase of the threshold voltage. The solution of the problem might be using the high-k dielectrics. Acknowledgements The work at CNSE, SUNY at Albany has been supported by the Materials Structures and Devices Focus Center (MSD Focus Center). The work at RPI has been supported by ONR (Project Monitor Dr. Colin Wood) and by the National Science Foundation under “Connection one” I/UCR center. The AlGaN/GaN transistors development at SET, Inc. has been supported under SBIR Phase II contracts from DARPA (M. Rosker) and ARL (P. Shah). Conclusion The dielectric constant of the HfO 2 on AlGaN was found ε HfO >23-24, which is close to the highest reported values for this material. No dielectric losses comparable with losses related to the 2D gas and small leakage current were found. The conductance measurements indicate low concentration of the interface traps in comparison with electron concentration on the AlGaN/GaN interface. Experimental Details The AlGaN/GaN heterostructures were grown by MOCVD on sapphire. They consisted of a 50-nm-thick AlN buffer layer, 0.4-mm- thick undoped GaN layer, followed by Al 0.2 Ga 0.8 N barrier layer, which was doped with silicon to approximately 2  10 18 cm -3. The Hall mobility and concentration of the 2d gas on the interface were μ=1600cm 2 Vs and n=1.33cm -2, respectively. The HfO 2 thin film was deposited by a reactive e-beam evaporation of Hf with O 2 flow directed from manual leak valve to a substrate. The SPECS EBE-1 (a mini e-beam evaporator from SPECS GmbH) with flux stabilization was used for the Hf evaporation. A custom design process chamber was pumped down to 5x10 -11 Torr. The process pressure was defined by flowing pure O 2 and maintained at 10 -6 Torr. The distance between the Hf source and the substrate was about 7 cm. The thickness of the deposited HfO 2 was d HfO  10nm. Control Sample: d AlGaN  20nm (from C at V=0) V t = -5.4V n=C 0 V t /q=1.25  10 13 cm -2 (in agreement with the Hall measurements.) As deposited HfO: Annealed HfO: ε HfO  23-24 ε HfO  26 (or higher) 20- 30% thickness reduction After [1]. Small leakage current in both directions should allow for the transistor operation both at negative and positive gate voltages [1]. C-V Characteristics Leakage Current Capacitance and Conductivity The conductivity above threshold is practically the same for both samples [1]. References 1. V. Tokranov, S.L. Rumyantsev, M.S. Shur, R.Gaska, S. Oktyabrsky, R. Jain, N. Pala, “The HfO2/AlGaN/GaN structures with HfO2 deposited at ultra low pressure using e-beam” phys.stat.sol. (RRL) 1, No. 5, 199-201 (2007)