| AVS 59th Annual International Symposium and Exhibition | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | Electrical Testing and Defects in III-V’s |
| Presenter: | G.J. Hughes, Dublin City University, Ireland |
| Authors: | G.J. Hughes, Dublin City University, Ireland L.A. Walsh, 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 |
In this work synchrotron radiation based hard x-ray photoelectron spectroscopy (HAXPES) measurements have been used to study the intrinsic electronic properties of high-k dielectric metal oxide semiconductor (MOS) structures on Si, GaAs and InGaAs substrates. The MOS structures were prepared with both high (Ni) and low (Al) workfunction metal layers 5nm thick on both n and p doped semiconductor substrates. CV and IV measurements were also performed on an identical sample set where the top metal contact was 160 nm thick to facilitate electrical measurements, and Ni was replaced with Ni/Au, 70/90 nm thick, respectively. The 4150 eV photon energy used in the HAXPES measurements gave a photoemission sampling depth of ~15 nm ensuring that signals were simultaneously detected from the substrate, the 8 nm thick dielectric layers as well as the top metal contact. The binding energy of core levels in photoemission 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. The MOS structures on ammonium sulphide passivated n (Si - 5x1017 cm-3) and p (Zn - 5x1017 cm-3) doped GaAs substrates were fabricated by the atomic layer deposition (ALD) of 8 nm thick Al2O3 dielectric layers. 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 that the Al2O3/GaAs interface is strongly pinned. Lattice matched 0.2 μm thick In0.53Ga0.47As layers, with both n and p doping (~4x1017 cm-3), were grown by MOCVD on InP n+ and p+ substrates, respectively. Al2O3 dielectric layers 8 nm thick were then deposited ex-situ by ALD on the native oxide and ammonium sulphide treated InGaAs surfaces. 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. Deposition of the metals with different workfunctions resulted in limited movement of the Fermi level, indicating the partially pinned nature of the InGaAs/Al2O3 interface. Corresponding changes in the potential across the dielectric layer were also measured.