The electronic structure of the Si(1 1 1):GaSe van der Waals-like surface termination has been determined by angle-resolved photoelectron spectro- scopy using photons in the energy range hν = 12–170 eV supplied by the BESSY and ALS synchrotron light sources. The Si(1 1 1):GaSe surface is isoelectronic to the passivated Si(1 1 1):H and Si(1 1 1):As surfaces, and also reflects the principal building block of layered chalcogenide GaSe single crystals. The electronic structure is discussed in relation to these systems. The chemical bond between the Si and Ga surface atoms is non-polar and therefore similar to the Ga–Ga bond in GaSe single crystals and also to the Si–Si bond in bulk silicon. This explains both the absence of a surface core-level shift in Si 2p photoelectron spectra of the terminated surface and the striking similarity between its observed band structure and that of bulk GaSe.
