Limit of efficiency of generation of hot electrons in metals and their injection inside a semiconductor using a semiclassical approach

Abstract

Hot electron generation in a metal and injection into a semiconductor is a crucial mechanism to convert sub band gap photons into free electrical charges inside a semiconductor. This process is of paramount importance for solar photocatalysis since the semiconductors involved often have a band gap too large for direct excitation with sun light, thus requiring a carrier transfer from an adjacent effective absorber, which in our case is a metal, to the semiconductor in order to initiate the envisaged photochemical reactions. Single interaction of a hot electron with a metal-semiconductor boundary is described by Fowler's law. In nanometer sized metals hot electrons, before they lose their energy, can interact several times with the boundary, which increases the probability of injection. To understand the efficiency of this process, to find ways to optimize it, and to determine its limits, an electron transport model based on a Monte Carlo approach is proposed. The numerical calculations provide an in-depth understanding of the impact of size and shape of the metal on the injection efficiency. Values are obtained that exceed the usual efficiency limits described by Fowler's theory.