There is a wealth of experimental results for excitations in bulk diamond-structure silicon. A good summary is provided in the book by Chelikowsky and Cohen.
Traditionally, optical reflectivity measurements were the popular[95, 96, 97, 98, 99, 100] method of measuring band structures. They have two main advantages over other optical probes. First, they are not over sensitive to surface conditions. The photon sampling length in semiconductors is of the order of a few thousand angströms. Since intrinsic surface perturbations in semiconductors heal within tens of angströms, optical measurements are insensitive to surface states. Secondly, reflectivity measurements have better resolution than other techniques with respect to band structure features which lie in or above the optical region. In some cases, this resolution may approach a few meV.
The more modern tool for probing the electronic structure of solids is photo-electron spectroscopy. In this technique the surface of a solid is bombarded with either X-ray or Ultraviolet radiation. The photons are absorbed in the bulk by a process which corresponds to a bulk excitation. The excited electrons then propagate to the crystalline surface and escape. By measuring the number of photoelectrons ejected with a specific energy for a given incident photon energy, one is able to probe the valence band density of states within the bulk solid.
One of the most useful implementations of photoelectron spectroscopy is the angle-resolved photoemission spectroscopy technique. This technique uses the conservation of momentum parallel to the surface to calculate the component of the bulk electron's momentum parallel to the surface. Hence one is able to measure not only the valence band density of states but also the valence bandstructure. It is also possible to measure the conduction bandstructure using the technique of inverse photoemission, which yields the energy and momentum of a photon emitted when an electron makes the transition from the conduction band to the valence band. All the experimental results for the bandstructure of silicon[102, 103, 104] quoted later in this chapter have been obtained using photoemission experiments.