Polarization dependence of Ge(111)2×1 surface-state absorption using photothermal displacement spectroscopy: A test of surface reconstruction models

The polarization dependence of surface-state absorption of Ge(111)2×1 single-domain surfaces has been directly measured using photothermal displacement spectroscopy. The absorption at 0.5 eV is maximum for incident light polarized perpendicular to the period-doubling direction of the 2×1 reconstruction. As the polarization direction is rotated, the absorption follows a ${cos}^2\theta$ dependence. This result supports the $\pi$-bonded chain model for the surface reconstruction, and is the same as that recently reported for the dangling-bond absorption of Si(111)2×1.