AVS 63rd International Symposium & Exhibition
    Electronic Materials and Photonics Monday Sessions
       Session EM-MoA

Paper EM-MoA3
Advances in High-k Dielectric Integration with Ga-polar and N-polar GaN

Monday, November 7, 2016, 2:20 pm, Room 102A

Session: Surface and Interface Challenges in Wide Bandgap Materials
Presenter: Charles Eddy, Jr., U.S. Naval Research Laboratory
Authors: C.R. Eddy, Jr., U.S. Naval Research Laboratory
C.R. English, University of Wisconsin
V.D. Wheeler, U.S. Naval Research Laboratory
D.I. Shahin, University of Maryland College Park
N.Y. Garces, U.S. Patent & Trade Office
A. Nath, U.S. Naval Research Laboratory
J.K. Hite, U.S. Naval Research Laboratory
M.A. Mastro, U.S. Naval Research Laboratory
T.J. Anderson, U.S. Naval Research Laboratory
Correspondent: Click to Email
Gallium- and nitrogen-polar GaN surfaces are subjected to a variety of pretreatments, including oxidation, before the application of high-k dielectrics by atomic layer deposition (ALD) in order to assess their ability to produce smooth, clean and electrically high-performing dielectric semiconductor interfaces. In terms of topographical and chemical cleanliness, a pretreatment with a wet chemical piranha etch (H2SO4:H2O2) was found to be optimum for both surfaces and, additionally, (NH4)2S is effective for N-polar surfaces. Both thermal and plasma oxidations were employed for controlled growth of native oxides. For Ga-polar surfaces, all native oxides were as smooth as pretreated surfaces, while for N-polar surfaces all native oxides are much rougher except for very short, high temperature oxidations. Thermal ALD high-k dielectrics, including Al2O3, HfO2 and ZrO2, were deposited on “optimally” treated surfaces. ALD Al2O3 films on Ga-polar surfaces are smoother for pre-treated surfaces than for as-received surfaces, whereas for N-polar surfaces the opposite is true. In general, ALD HfO2 films on Ga-polar surfaces are rougher (0.8 nm rms) than Al2O3 films (0.1 nm rms), whereas for piranha treated N-polar surfaces HfO2 films are smoother than Al2O3 films. ZrO2 films are smoother than HfO2 but rougher than Al2O3 films. For Ga-polar surface, capacitance-voltage measurements of simple Al2O3 (measured k = 9) capacitors show the smallest hysteresis for unintentionally oxidized surfaces (0.37 V), whereas simple HfO2 (measured k = 14) capacitors show the smallest hysteresis for a thermal GaOx at the interface (0.1 V). In both cases, the thicker the GaOx at the interface the larger the negative threshold voltage shift – suggesting an electron trap. Calculated total trapped charges associated with the dielectrics range from 3.2x1011 cm-2 (for HfO2 on thermally oxidized GaN) to 1x1012 cm-2 for Al2O3 on thermally oxidized GaN and HfO2 on plasma oxidized GaN. Finally, the leakage current density for nearly all capacitors is <10-5 A-cm-2 for up to a +8V bias. Interestingly, without additional GaN oxidation, ZrO2 films present a significant positive threshold shift which could be beneficial for enhancement-mode transistor operation. Further details of ZrO2 performance on “optimally” treated Ga-polar surfaces will also be presented.