Anti-Fowler Temperature Regime in Photoemission from <i>n</i>-Type Semiconductors with Surface Accumulation Layer

Abstract

According to the Fowler theory and numerous experiments the quantum efficiency for photoemission from conductors increases with temperature. Here we show that an opposite temperature dependence is also possible, when the photoemission is from quasi-metallic surface accumulation layers of n-type semiconductors. This is due to the temperature dependence of the Fermi level energy in semiconductors. The Fermi level energy increases with decreasing temperature; this leads to a decrease of the semiconductor work function and consequently an increase of the quantum efficiency photoemission at constant value of absorbed light quanta of energy. We have calculated this effect for electron accumulation layer in n-GaN, induced by adsorption of positively charged cesium or barium ions. It is found that at low temperatures near liquid nitrogen, the quantum efficiency for photoemission increases to near 55%, which is comparable to the largest values, reported for any known photo-cathodes. This phenomenon may prove useful for efficient photo-cathodes operating at low temperatures.