Observation of momentum space semi-localization in Si-doped   $\beta$-Ga$_2$O$_3$
  We performed an angle-resolved photoemission spectroscopy study of Si-doped $\beta$-Ga$_2$O$_3$. We observed very small photoemission intensity near the Fermi level corresponding to non-dispersive states assigned to Si impurities. We show evidence for a quantization of these states that is accompanied by a confinement in the momentum space consistent with a real-space finite confinement observed in a previous scanning tunneling microscopy study. Our results suggest that this semi-localization in the conjugate spaces plays a crucial role in the electronic conduction of this material. 
P. Richard, T. Sato, S. Souma, N. Nakayama, H. W. Liu, K. Iwaya, T.   Hitosugi, H. Aida, H. Ding and T. Takahashi
cond-mat.mtrl-sci