  Phase change alloys are used for non-volatile random access memories
exploiting the conductivity contrast between amorphous and metastable,
crystalline phase. However, this contrast has never been directly related to
the electronic band structure. Here, we employ photoelectron spectroscopy to
map the relevant bands for metastable, epitaxial GeSbTe films. The constant
energy surfaces of the valence band close to the Fermi level are hexagonal
tubes with little dispersion perpendicular to the (111) surface. The electron
density responsible for transport belongs to the tails of this bulk valence
band, which is broadened by disorder, i.e., the Fermi level is 100 meV above
the valence band maximum. This result is consistent with transport data of such
films in terms of charge carrier density and scattering time. In addition, we
find a state in the bulk band gap with linear dispersion, which might be of
topological origin.
