Infrared field assisted photoemission of metal-semiconductor structures

We present an experimental study of the effect of an electric field upon the photoemission properties of Ag/InP metal-semiconductor structures. The electron affinity of the structure is lowered by cesium and oxygen coadsorption so that photoemission can be observed under near bandgap light excitation in a p-type sample. Two distinct effects occur upon reverse biasing. The raising of the energy of the conduction band in the bulk with respect to the position of the vacuum level produces a strong increase of the photoemission yield of the system. Furthermore, in the high electric field region near the surface, photoelectrons are transferred to indirect valleys by emission of optical phonons. This latter effect is demonstrated in a spectacular way by high resolution energy analysis of the emitted electrons: above a reverse bias of 0.8 V, one observes a strong modification of the shape of the energy distribution curve which is a direct proof for the relevance of intervalley transfers.