Field emission properties of boron- and phosphorus-doped diamond

Field emission properties of boron (B)-doped polycrystalline diamond after hydrogenation and oxidization were investigated to understand the field emission process. Temperature dependences of field emission from heavily and lightly B-doped polycrystalline diamond were also characterized. The threshold voltage of hydrogen (H)-terminated B-doped polycrystalline diamond was lower than that of oxygen (0)-terminated B-doped polycrystalline diamond. The change in field emission properties can be explained by the difference in electron affinity of the diamond surface from Fowler-Nordheim plots. Heavily B-doped polycrystalline diamond showed lower threshold voltages than lightly B-doped polycrystalline diamond. The threshold voltage of lightly B-doped polycrystalline diamond decreased with increasing temperature, while field emission properties of heavily B-doped diamond were independent of temperature. This is attributed to electron emission from the valence band maximum of lightly B-doped diamond and from the boron impurity level of heavily B-doped diamond. Field emission properties of H- and O-terminated heavily phosphorus (P)-doped homoepitaxial diamonds were also characterized. They show that the threshold voltage of H-terminated heavily P-doped diamond is higher than that of O-terminated heavily P-doped diamond. This is contrary to the results of B-doped diamond. We assume that an internal barrier is generated which prevents electrons from propagating to the surface and from escaping into vacuum.