AVS 59th Annual International Symposium and Exhibition
    Applied Surface Science Tuesday Sessions
       Session AS-TuP

Paper AS-TuP7
A Combined HAXPES and Electrical Characterisation Study of Si and III-V based MOS Structures

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: Applied Surface Science Poster Session
Presenter: L.A. Walsh, Dublin City University, Ireland
Authors: L.A. Walsh, Dublin City University, Ireland
G.J. Hughes, Dublin City University, Ireland
P.K. Hurley, Tyndall National Laboratory, Ireland
J.H. Lin, Tyndall National Laboratory, Ireland
J.C. Woicik, National Institute of Standards and Technology
Correspondent: Click to Email
The aim of this study was to use synchrotron radiation based HAXPES measurements to study the intrinsic electronic properties of both Si and III-V based MOS structures. High quality thermally grown SiO2 layers, with a thickness of 8 nm, were grown on both n (5x1015 cm-3) and p (5x1015 cm-3) doped silicon. While Al2O3 layers 8nm thick were deposited on both n (Si - 5x1017 cm-3) and p (Zn - 5x1017 cm-3) doped GaAs, and n and p (~ 4x1017cm-3for both) doped InGaAs substrates. All substrates were treated by a wet chemical ammonium sulphide based passivation treatment. The samples for HAXPES analysis were capped with 5 nm Ni or Al blanket films by electron beam evaporation. For electrical characterisation, Ni/Au (70 nm/90 nm) and Al (160 nm) gate electrodes were patterned by electron beam evaporation and a lift off lithography process. HAXPES measurements using a photon energy of 4150 eV were used to probe the MOS structures in order to investigate the differences in substrate core level binding energies caused by changes in doping type, and metal work function The sampling depth for these high energy photons was sufficient to detect core level peaks originating from the substrate, the 8 nm thick dielectric layer, and the top metal contact. The binding energy of core levels in photo emission are referenced with respect to the Fermi level, therefore changes in the binding energy of a particular core level reflect differences in the position of the Fermi level in the semiconductor band gap. For the MOS structures fabricated using SiO2/Si, changes in the Fermi level positions and differences in the potential drops across the dielectric layers have been directly correlated with the metal workfunction differences observed in the CV and GV measurements. A binding energy difference of 0.6 eV was measured between the GaAs core levels of the n and p doped substrates, independent of metal work function indicating the strong Fermi level pinning present at the Al2O3/GaAs interface. Binding energy measurements for the core levels of native oxide covered n-type doped InGaAs substrates with no metal cap were found to be consistently (~0.3 eV) higher than p-type samples reflecting the fact that the Fermi level is in a different position in the band gap. A binding energy difference of 0.25eV for the core levels of the n and p samples just with the Al2O3 dielectric layer present, indicating different Fermi level positions in the band gap. Deposition of the different workfunction metals resulted in limited change in the InGaAs core level binding energies, indicating the partially pinned nature of the Al2O3/InGaAs interface.