Evidence for space charge in atomic layer epitaxy ZnS:Mn alternating-current thin-film electroluminescent devices

Electrical and optical measurements of ZnS:Mn alternating-current thin-film electroluminescent (ACTFEL) devices grown by atomic layer epitaxy provide evidence for the existence of space charge within the bulk ZnS layer. Blue luminescence is observed during the falling edge of an applied voltage pulse when the ACTFEL device is operated at low temperature. This blue luminescence is attributed to donor-acceptor pair radiative recombination in which chlorine is identified as the donor and a zinc vacancy as the acceptor. This luminescence identification leads to determination of the origin of space charge as arising from impact ionization of the zinc vacancy.