Digging up bulk band dispersion buried under a passivation layer

We report angle-resolved photoemission spectroscopy (ARPES) on a GaAs thin film protected by an amorphous As layer with thickness exceeding the typical probing depths of vacuum-ultraviolet rays up to similar to 100 eV. Increasing the probing depth by increasing photon energy into the soft x-ray (SX) region of several hundred eV clearly exposes the bulk band dispersion of the GaAs underlayer without any surface treatment. Our results demonstrate that the use of SX-ARPES enables access to the three-dimensional band dispersion of buried underlayer through an amorphous overlayer. This opens frontiers in diagnostics of authentic momentum-resolved electronic structure of protected thin-film heterostructures. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770289]