  Nonlinear and hysteretic electrical devices are needed for applications from
circuit protection to next-generation computing. Widely-studied devices for
resistive switching are based on mass transport, such as the drift of ions in
an electric field, and on collective phenomena, such as insulator-metal
transitions. We ask whether the large photoconductive response known in many
semiconductors can be stimulated in the dark and harnessed to design electrical
devices. We design and test devices based on photoconductive CdS, and our
results are consistent with the hypothesis that resistive switching arises from
point defects that switch between deep- and shallow-donor configurations:
defect level switching (DLS). This new electronic device design principle -
photoconductivity without photons - leverages decades of research on
photoconductivity and defect spectroscopy. It is easily generalized and will
enable the rational design of new nonlinear, hysteretic devices for future
electronics.
