Ultralow-frequency spontaneous oscillations of the current in   polycrystalline silicon
  We report results of experimental study of ultralow-frequency spontaneous oscillations of the current in polycrystalline silicon films subjected to strong electric fields at room temperature. 
V.A. Dorosinets, N.A. Poklonski, V.A. Samuilov, V.F. Stel'makh
cond-mat.dis-nn cond-mat.mes-hall cond-mat.mtrl-sci