The phototransistor action of a reverse-biased Au/CaF₂[3–7 ML]/n-Si(1 1 1) structure

Metal–ultra-thin insulator–semiconductor (MIS) tunnel structures with a high-quality ultra-thin epitaxial fluoride layer have been fabricated on n-Si wafers. Under the reverse bias, these structures have been experimentally shown to amplify photocurrent. They can therefore be treated as MIS tunnel emitter bipolar phototransistors. The gain value reaches 102–103, and is due to the asymmetry between conduction-band and valence-band tunneling. The importance of the valence-band component has been elucidated. The experimental data have been well reproduced by simulations considering the conservation of the transverse wave vector of tunneling particles. The current multiplication effect was observed within the voltage range up to the structure overload. After the insulator damage, the structure ceased to exhibit gain rendering a photodiode.