Discharge lamp and discharge electrode having an electron-emitting layer including a plurality of protrusions separated by grooves

A discharge lamp comprising:

• a sealed-off tube filled with a discharge gas;
• an electron-emitting layer including a supporting base having a flat top surface, formed of a wide bandgap semiconductor and provided on the inner surface of the sealed-off tube, wherein a plurality of protrusions are provided at an upper portion of the supporting base, wherein the protrusions are separated by a plurality of grooves cut from the top surface toward a bottom surface of the supporting base, the depth of the grooves are smaller than a thickness of the supporting base, the top end surfaces of the protrusions are parallel to the top surface of the supporting base, for each protrusion viewed from above a perpendicular center line from the plane of the top end surface of the protrusion, sidewalls of the protrusion are unseen, dangling bonds of the wide bandgap semiconductor at the sidewalls are terminated with hydrogen atoms;
• and
• an external discharge electrode provided on the outer surface of the sealed-off tube, opposing to the electron-emitting layer.