Relevance of GaAs(001) Surface Electronic Structure for High Frequency Dispersion on N-Type Accumulation Capacitance
Tun-Wen Pi1*, W. S. Chen1, Y. H. Lin2, Y. T. Cheng3, K. Y. Lin2, T. W. Chang2, H. W. Wan2, C. P. Cheng3, J. Kwo4, M. Hong2
1Science Division, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Grad. Inst. of Appl. Phys. and Dept. of Physics, National Taiwan University, Taipei, Taiwan
3Department of Electrophysics, National Chiayi University, Chiayi, Taiwan
4Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
* presenting author:Tun-Wen Pi,
This study investigates the origin of long-puzzled high frequency dispersion on the accumulation region of capacitance-voltage characteristics in a n-type GaAs-based metal-oxide-semiconductor. The literature unanimously reports that the atomic-layer-deposited (ALD) Al2O3 and HfO2 on n-type GaAs(001) samples show profoundly greater frequency dispersion than the p-type sample in the accumulation region of C-Vs, irrespective of dielectric oxides. In this report, we employ high-resolution core-level photoemission to probe the interfacial electronic structure of the noble metals on the  GaAs(001)-2×4 surfaces to tackle the origin of the great frequency dispersion shown in the C-Vs at accumulation region for the n-GaAs(001) samples. We here demonstrate that the surface electronic structure of the pristine surface plays a key role. The Pauling electronegativities of As, Ga, Ag, and Au are 2.18, 1.81, 1.93, and 2.54, respectively. It is then expected that Au is regarded as an acceptor and Ag as an amphoteric metal. However, the GaAs(001) surface inclines to particularly trap the negative charges from the noble metals with high Pauling electronegativities. Probed adatoms of high Pauli electronegativity, such as Ag and Au, were deposited onto as-grown 2 GaAs(001)-2×4 surfaces and were analyzed by high-resolution core-level synchrotron radiation photoemission. The noble-metal adatoms in the sub-monolayer coverage bonded intimately with the GaAs surface atoms without causing surface disruption. The supposed charge acceptors of the noble-metal adatoms anomalously donated charge onto the contacted As/Ga atoms. The GaAs surface atoms then tended to drain electrons, and if not properly passivated, they would trap those electrons accumulated at the oxide and semiconductor interface under the positive bias voltage. Remnant of unpassivated surface As atoms indeed existed in the Al2O3/n-GaAs(001)-2×4 as well as in the n-GaAs(001)-4×6 interfaces, thereby causing high frequency dispersion in the accumulation region. For the p-type semiconductor, electrons under a negatively biased condition were expelled from the interface, thereby avoiding becoming trapped.

Keywords: III-V, interface, core-level spectra, frequency dispersion