Quasiballistic electron emission from porous silicon diodes

Porous Si PS. diodes operate as efficient cold electron emitters as well as electroluminescence EL. devices. The PS layers are formed on the surface of heavily doped n-type Si substrates by conventional photoanodization in an ethanoic HF solution. When a positive bias voltage is applied to the thin Au top electrode with respect to the substrate in vacuum, electrons are uniformly emitted through the Au film. This is presumably due to tunneling of hot electrons generated in PS. An appropriate combination of structural control and thermal oxidation for PS produces quite stable electron emission without any fluctuations or spike noises. The behavior of output electron energy distribution strongly suggests that electrons are emitted quasiballistically. Similar results are also observed in diodes prepared on polycrystalline Si films. The electrical function of PS as a ballistic transport medium is discussed, including the advantageous features of this device as a novel electron source. q1999 Published by Elsevier Science B.V. All rights reserved