Negative electron affinity GaN photocathode with Mg delta-doping

Mg δ-doping GaN material is grown by MOCVD and activated by Cs/O in UHV subsequently, then NEA GaN photocathode can be obtained. Compared with the p-type uniform doping, the δ-doping NEA GaN photocathode shows better photoemission performance, and the photocurrent is twice as the uniform. The QE of δ-doping and uniform doping are 24% and 10% at 5.16 eV, respectively. The hole concentration of δ-doping and uniform doping are 8.7 × 1017 cm−3 and 3.3 × 1017 cm−3, while better crystal quality for δ-doping is proved by the XRD results simultaneously. Profited from the higher hole concentration and better crystal quality, the P and L of δ-doping NEA GaN photocathodes are raised to 0.51 and 258 nm, respectively. After introduction of O during the activation, the photocurrent of uniform doping GaN photocathode has obvious improvement, however, it is even worse than before for the δ-doping. On the basis of [GaN(Mg)- Cs]:[O-Cs] model, it is found that the surface roughness is beneficial for improving photocurrent during the Cs/O alternating activation stage.