Sources of photoemission in Na3Sb thin films

摘要

Na3Sb thin films were formed by first depositing an Sb layer and then depositing Na from a molecular‐beam source; the Na‐Sb reaction took place at room temperature. The average film composition during Na deposition was determined with a quartz crystal microbalance. Photoemissive spectral yield and photoelectron energy distribution data were obtained as a function of film composition. Values for band‐bending parameters, photosensitive layer thickness, and photothreshold energy were determined from an analysis of the spectral yield data. In the Na to Sb ratio range of approximately 2 : 1 to 3 : 1, the photosensitive layer thickness increases from less than 20 Å to greater than 300 Å, suggesting that the Na3Sb growth proceeds from the surface at the completion of Na2Sb growth. The threshold region of the spectral yield curves fits a model for indirect transitions from surface states at the Fermi energy. The energy distribution data confirm that the transitions are indirect. A separate peak in the energy distribution data is attributed to emission from bulk donor states.