Single-carrier impact ionization favored by a limited band dispersion
  A critical requirement for high gain and low noise avalanche photodiodes is the single-carrier avalanche multiplication. We propose that the single-carrier avalanche multiplication can be achieved in materials with a limited width of the conduction or valence band resulting in a restriction of kinetic energy for one of the charge carriers. This feature is not common to the majority of technologically relevant semiconductors, but it is observed in chalcogenides, such as Selenium and compound I2-II-IV-VI4 alloys. 
A. Darbandi, and O. Rubel
cond-mat.mtrl-sci physics.comp-ph