Photoemission from GaN

Photoemissive yield measurements were performed on degenerate n-type and semi-insulating GaN for heat-cleaned and for cesiated surfaces. The photoemissive threshold for heat-cleaned n-type material occurs at 4.1 eV, while that for semi-insulating material is beyond 5.5 eV, the experimental spectral range. From these measurements an upper and a lower limit of the electron affinity of heat-cleaned GaN is derived, namely 4.1 > χ > 2.1 eV. The threshold for cesiated surfaces on both materials is lowered to 1.5 eV, and the photoyield curve exhibits a second threshold at about 3.4 eV. The occurrence of negative electron affinity is suggested for cesiated semi-insulating GaN.