Generalizable Density Functional Theory Based Photoemission Model for the Accelerated Development of Photocathodes and Other Photoemissive Devices

In this work, we have developed an ab initio photoemission model that accurately describes the photoemission process for the most diverse range of photocathode materials to date. Compared to previous photoemission models, this is accomplished by considerably reducing the number of approximations and assumptions used in representing the photoemission process and the photoemitting material itself. Notably, our model directly includes the full electronic structure of the material, photoexcitation probabilities for all direct optical transitions, and an improved surface-vacuum barrier transmission probability. To test the performance of our model, we perform validations with experimental measurements for all photocathode materials studied in this work. Whereas previous models have often qualitatively disagreed with the measured photoemission properties of some materials, our model is found to provide quantitative agreement with experimental measurements for all tested materials. As an example, our method predicts the root-mean-square transverse momentum of electrons emitted from PbTe up to an excess energy of 1.0 eV with a mean absolute error that is similar to 5x less than from previously derived expressions. Perhaps more importantly, our model is able to match experimentally observed decreases in intrinsic emittance with increasing photon energy-a feat that current analytical models are unable to achieve. We expect that the broad applicability of our model will greatly accelerate the rate of discovery, characterization, and scientific understanding of photocathodes and other photonic devices.