PHOTORESPONSE CHARACTERISTICS OF THIN FILM NICKEL-NICKEL OXIDE-NICKEL TUNNELING JUNCTIONS

An experimental investigation of the photoresponse characteristics of thin film planar Ni-NiO-Ni tunneling junctions is presented. The DC current-voltage characteristic curves of these devices were also measured, for both polarities of bias voltage, and with and without laser light illumination. Photoresponse characteristics were measured as a function of incident photon energy in the visible region of the spectrum, on-off modulation rate of the incident light, thickness of the metallic layers, and bias voltage.; Three types of junctions were investigated. All three junctions were formed on glass substrates by constructing two 10-(mu)m wide strips of nickel that crossed at right angles, with an approximately 8 to 10(ANGSTROM) thick layer of nickel oxide separating the two metal layers. The first type of device consisted of nickel layers approximately 750(ANGSTROM) in thickness, separated by a thin nickel oxide layer formed by sputter etching the lower nickel electrode in an argon-oxygen atmosphere. The second and third types of junctions were formed by directly depositing a thin layer of nickel oxide, using a reactive sputtering process, on bottom nickel electrodes of 500(ANGSTROM) and 150(ANGSTROM) thickness, respectively. The top electrode was 150(ANGSTROM) thick for both of these junctions.; The observed photoresponse characteristics were consistent with a mechanism of photoassisted tunneling, in which inelastic electron-electron collisions within the metal layers played a significant role in determining the energy distribution of the tunneling electrons. The occurrence of such collisions heavily skewed the energy distribution of electrons that reached the oxide layer toward lower energies, with the skewness increasing as a function of metal thickness. It also accounted for the rapid heating of the junction and strong thermal characteristics of the observed response.