Alkali-metal-induced Fermi-level and two-dimensional electrons at cleaved InAs(110) surfaces

Low-temperature Hall measurements have been performed on two-dimensional electron gases (2DEGs) induced by deposition of Cs or Na on in situ cleaved surfaces of $p$-type InAs. The surface donor level, at which the Fermi energy of the 2DEG is pinned, is calculated from the observed saturation surface electron density using a surface potential determined self-consistently. The results are compared to those of previous photoelectron spectroscopy measurements.

Figure 1

Schematic view of the experimental setup mounted in a low-temperature vacuum chamber. Alkali metals are deposited from the aluminosilicate ion source (Refs. 14, 15, 16) which is well out gassed before in situ cleaving. The grid is used to reduce the electric field near the sample which may lead to nonuniform distribution of the adsorbates.

Figure 2

Conduction electron density in the inversion layer as a function of the surface atomic density of adsorbates. Data for Ag are taken from Ref. 11. The dashed straight line indicates a slope of unity.

Figure 3

Calculated $N_s$ vs Fermi energy ${\epsilon }_F$ measured from the conduction band minimum at the surface. The solid line is calculated using $V\left(z\right)$ determined self-consistently. The results obtained from the classical approximation for $V\left(z\right)$ (Ref. 17) are also plotted as the dotted line. Depletion layer charges arising from ionized acceptors were taken into account and their potential was replaced by a constant electric field.[20] $N_1$ and $N_2$ are the subband electron densities while $N_0=N_s-N_1-N_2$ is not shown explicitly.

Figure 4

The maximum ${\epsilon }_F$ position measured from the conduction band minimum at the surface as a function of the first ionization energy of the corresponding atom. The open and filled symbols indicate depositions at room and low (4.2–20 K) temperatures, respectively: circles, this work; triangles, Ref. 5; inverted triangles, Ref. 7; diamonds, Refs. 8, 9; squares, Ref. 10. Data obtained at 80 K (plus) and 200 K (crosses) in Ref. 10 are also shown.