Influence of surface states on tunneling spectra of $n$-type GaAs(110) surfaces

Influence of surface states on tunneling spectra of $n$ -type GaAs(110) surfaces

Nobuyuki Ishida, Kazuhisa Sueoka, and R. M. Feenstra

Phys. Rev. B 80, 075320 – Published 31 August 2009

Abstract

We show that surface states within the conduction band of $n$ -type GaAs(110) surfaces play an important role in reducing the tunneling current out of an accumulation layer that forms due to an applied potential from a nearby probe tip. Numerical computation of the tunneling current combined with an electrostatic potential computation of the tip-induced band bending (TIBB) reveals that occupation of the surface states limits the TIBB, thus leading to the limitation of the accumulation. As a result, the tunneling current out of the accumulation layer is strongly suppressed, which is in quantitative agreement with the experiment.

Received 17 May 2009

DOI:https://doi.org/10.1103/PhysRevB.80.075320

Authors & Affiliations

Nobuyuki Ishida¹, Kazuhisa Sueoka¹, and R. M. Feenstra^2,*

¹Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814, Japan
²Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

^*feenstra@cmu.edu

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Vol. 80, Iss. 7 — 15 August 2009

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Images

Figure 1
(a) Schematic diagram of energy bands with a varying electrostatic potential (TIBB), showing the valence-band maximum $E_{V}$ and the conduction-band minimum $E_{C}$ . The sample Fermi level is denoted by $E_{F}$ with the tip Fermi level at $E_{F} + e V$ where $V$ is the sample-tip voltage. The band bending at the surface is denoted by $ϕ_{0}$ . Quantum effects within the semiconductor are illustrated in (b) and (c) for wave-function tailing through a depletion region and for localized accumulation state formation, respectively.Reuse & Permissions
Figure 2
(Color online) (a) Tunneling spectra of the $n$ -type GaAs(110) surface from the experiment and theory. Solid line shows the experimental data. Open circles and triangles show the theoretical computation with and without inclusion of the surface states, respectively. (b) TIBB as a function of bias voltage computed with a 3D potential computation with (open circles) and without (open triangles) including the surface states. The TIBB is measured relative to the potential energy at a point far inside the semiconductor. The inset shows the density distribution of the surface states assumed in this computation.Reuse & Permissions
Figure 3
(Color online) [(a) and (b)] Each component of the tunneling conductance computed with [in (b)] and without [in (a)] the surface states. Dotted lines show the total conductance. Open circles and squares show the conductance from the extended and localized states of the CB, respectively. Open triangles show the conductance from the extended states of the VB.Reuse & Permissions
Figure 4
(Color online) Dependence of the energy position of the surface state on the tunneling spectra. Solid line shows the experimental data. Open circles and triangles show the theoretical results with a $E_{S S}$ value of 1.75 and 1.78 eV, respectively.Reuse & Permissions
Figure 5
(Color online) Comparison of the effect of the surface pinning with the low tunneling probability. Solid line is the experimental data. Open circles and triangles show the theoretical computation with taking into account the inclusion of either the surface pinning or the low tunneling probability arising from the momentum dependence, respectively.Reuse & Permissions
Figure 6
(Color online) Electrostatic potential energy $ϕ (0, z)$ and energies of localized states (heavy lines) relative to the CB minimum. Also shown are the charge densities of localized states $ρ_{1} (0, z)$ and $ρ_{2} (0, z)$ , and the charge density of extended states $ρ_{E} (0, z)$ . All quantities refer to their values along the central axis of the problem $r = 0$ and are evaluated at a sample-tip voltage of $- 1.35 V$ . The inset shows $ρ_{E} (0, 0)$ as a function of sample-tip voltage.Reuse & Permissions

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