One-dimensional electronic states in ${\text{Ga}}_2{\text{Se}}_3$ on Si(001):As

Gallium selenide $\left({\text{Ga}}_2{\text{Se}}_3\right)$ is a III-VI chalcogenide material whose intrinsic cation vacancy ordering into one dimensional chains has been predicted to result in a one dimensional band at the valence-band maximum (VBM). The electronic structure of ${\text{Ga}}_2{\text{Se}}_3$ thin films on Si(001):As is studied with angle-resolved photoemission spectroscopy. The integrated density of states and the dispersion exhibit good agreement with that predicted by published density-functional theory results. Consistent with a one dimensional state, the electronic states at the VBM show no dispersion perpendicular to the vacancy chains. The Se-Ga bond length from extended x-ray absorption fine structure is $2.34\text{Å}$. Low-energy electron-diffraction results indicate that the surface is characterized by nanometer-scale (111) facets, consistent with previous scanning tunneling microscopy results.

Figure 1

(Color online) LEED pattern from ${\text{Ga}}_2{\text{Se}}_3$ film at (a) $\sim 105\text{eV}$, (b) $\sim 120\text{eV}$, and (c) $\sim 135\text{eV}$. (d) Intensity as a function of beam energy ($\text{white}=\text{more}$ intensity) for all the points along the line connecting the (1,1) and $\left(1,-1\right)$ spots scaled to give a fixed separation between those two spots. (e) STM image showing two-domain wirelike structure of ${\text{Ga}}_2{\text{Se}}_3$ found by Ohta et al. (Ref. 10); horizontal scale bar (50 nm) and substrate orientation are indicated.

Figure 2

(Color online) Integrated density of electronic states measured with ARPES (thin red) and total density of states plus breakdown by atomic species predicted by Peressi et al. using density-functional theory with LDA (thick black reproduced with permission from Ref. 7).

Figure 3

(Color online) (a) Normal-emission valence-band spectra from ARPES. Spectra with increasing $k_z$ ($0.043{\text{Å}}^{-1}$ increment) are offset to separate them. Black bold spectra are at $\Gamma$ $\left(k_z\sim 7.0{\text{Å}}^{-1}\right)$ and Z $\left(k_z\sim 5.8{\text{Å}}^{-1}\right)$. See labels at right. (b) ARPES spectra from $\Gamma$ along $k_x$ ($0.080{\text{Å}}^{-1}$ increment). The black spectra are at $\Gamma$, Y (the BZ boundary along $\Gamma \text{Y}$), ${\Gamma }^{\prime }$ (a $\Gamma$ point along $\Gamma \text{Y}$), and X (the BZ boundary along $\Gamma \text{X}$, which is also another Y point along $\Gamma \text{Y}$). A shoulder at the valence-band maximum shows little dispersion with $k_z$ and is emphasized with a vertical black line—it exhibits no dispersion along $k_x$.