We successfully observed electron emission from hydrogenated diamond (111) p+-i-n+
junction diodes. Here, p+- and n+
-layers mean that the boron and phosphorous impurity concentrations in these layers are around 1020 cm-3. Then the p+
-layer on top of the diode suppresses electron emission from the top-surface area. The heavily doped layers also play an important role to obtain high diode and emission currents. The emission started when the applying bias voltage was equal to the built-in potential, and the emission current reached to over 1 μA at room temperature operation. With taking into account our previous photoemission yield spectroscopy results and with the very high binding energy of free excitons of 80 meV in diamond, we suggested that the electron emission was derived from free excitons generated in the i-layer of the diodes.