SELF-SUSTAINED OSCILLATIONS IN UNDOPED A-SI-H

Self-sustained oscillations and fluctuations have been observed in und oped hydrogenated amorphous silicon (a-Si:H) thin films when small por tions of the sample were biased using coplanar electrodes. After subje cting the samples to very high voltages several times, the current flo w becomes unstable. At constant voltage the current continuously incre ases ending in the irreversible formation of visible channels between the electrodes which exhibit an almost periodic structure. During this process of pattern formation random fluctuation as well as periodic s ingle-frequency and mode-locked multiple-frequency current oscillation s and random telegraph noise have been detected. These phenomena are a ttributed to microcracks in the sample which change their resistivity by the hopping of hydrogen between different binding configurations.