Field-assisted infrared photoemission of metal-semiconductor structures

The work function of a semiconductor may be lowered using a surface treatment. Very efficient commercial photomultiplier tubes are built by this technique, starting from a semiconductor crystal. We first recall the principles of their operation and give a physical insight into the phenomena which determine their infrared energy cut-off. We show that this operation threshold can be extended towards smaller photon energies by application of an electric field. The use of the technique of high-resolution energy analysis of photoemitted electrons is discussed and appears to be a very powerful approach to the elucidation of the fundamental features of field-assisted photoemission. These well characterized systems, important for practical applications, are also very exciting from a fundamental point of view. The physical phenomena involves, which are directly connected with problems encountered in the design of ultra-fast electron devices, are discussed in the light of our experimental results obtained on Ag/InP metal-semiconductor structures.