Cs₃Sb and Ag-O-Cs Semiconductors as Diode Detectors for Low Energy Photon and Charged Particle Detection

Diode detectors for photons and charged particles (ions, e) and energy measurements use Si, Ge and many others. For very low energy photons, Si(Ge) pair energies Ep=3.6 eV(2.98eV) are to large for many applications, and usually require cooling for low noise. Semiconductor materials used for vacuum photocathodes have much lower Ep: Cs₃Sb (S-11)~2eV pair energy; Cs-Ag-O (S-1) averaged pair energy/work function Ep=0.7 eV, and studies have shown that in small patches that the pair energy/work function is a remarkably low Ep = 0.4 eV. We study atomic layer assembly techniques [ALD, MBE, low-temp pulsed-CVD] to make precisely structured Ag-Cs-O to achieve the lowest pair energy, and Cs₃Sb for sensors with low energy threshold operating at room temperatures. The Cs₃Sb bandgap Eg =1.6 eV is larger than the Eg =1.1. eV of Si, yet with a lower Ep=2 eV. The large Eg of Cs₃Sb compared with Si inhibits thermal energy from promoting carriers above the Fermi level, thereby operating with minimal or no cooling for detecting low energy photons or ions. Atomic layer assembly techniques can be used to protect the cesiated materials from air and water vapor with films that are effectively transparent to radiation – single layer graphene is a standard deposited material; 1 layer excludes He. Graphene has been deposited on Cs₃Sb photocathodes for protection from air and degradation.