Figure 1: Simplified band diagram showing a PETE device with a heterostructure cathode.

The cathode is separated by a vacuum gap from an anode at lower temperature and lower work function φ_A. PETE in the cathode occurs in three steps: photoexcitation, transport and emission. The heterostructure splits the emission step in two: internal PETE and external photoemission. The band gaps are denoted by E_g,absorber and E_g,emitter, the difference in energy between the conduction band minima in the absorber and nanoscale emitter is ΔE_CB, and schematic thermal distributions are shown at both the absorber/emitter interface and at the emitter/vacuum interface. The cathode’s work function φ_C is the difference between the cathode Fermi level E_F and the vacuum level at the emissive surface. This article focuses on the cathode side of the device, examining a heterostructure based on GaAs coated with Cs-O to lower its work function.