Quasiballistic electron emission from porous silicon diodes

Porous Si (PS) diodes operate as efficient cold electron emitters as well a s 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 thi n Au top electrode with respect to the substrate in vacuum, electrons are u niformly emitted through the Au film. This is presumably due to tunneling o f hot electrons generated in PS. An appropriate combination of structural c ontrol 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 quasiballi stically. Similar results are also observed in diodes prepared on polycryst alline Si films. The electrical function of PS as a ballistic transport med ium is discussed, including the advantageous features of this device as a n ovel electron source. (C) 1999 Published by Elsevier Science B.V. All right s reserved.