Role of the cesium antimonide layer in the Na2KSb/Cs3Sb photocathode

When radiation of sufficiently high energy is incident on the surface of a semiconductor photocathode, electrons are excited from the valence band to the conduction band and these may contribute to the photocurrent. The photo current in a single-layer cathode is found to be small, because of collisio ns within the cathode material, the electron affinity condition, etc. It is observed that when a thin layer of n-type cesium antimonide (Cs3Sb) is dep osited over a p-type layer of sodium potassium antimonide (Na2KSb), there o ccurs a sharp rise in the photocurrent. The causes for the dramatic increas e in the photocurrent obtainable from a sodium potassium antimonide cathode , by depositing a thin layer of cesium antimonide are analyzed in this arti cle. It has been shown that the interface between sodium potassium antimoni de and cesium antimonide can result in lowering of the electron affinity to a level below the bottom of the conduction band of sodium potassium antimo nide. The drift field that arises at the heterointerface enables the electr ons to reach the surface, leading to the emission of almost all the photoge nerated electrons within the cathode. The processes involved in photoemissi on from such a double-layer cathode are examined from a theoretical point o f view. The spectral response of the two-layer cathode is also found to be better than that of a single-layer cathode. (C) 2001 American Institute of Physics.