Free-exciton recombination emission of 235 nm in wavelength is obtained by
current injection at room temperature from a diamond-based pn junction diod
e composed of B-doped crystal grown by high-temperature, high-pressure synt
hesis and a S-doped homoepitaxial layer grown by the chemical vapor deposit
ion method. The diode shows a clear rectification characteristic and a high
external quantum efficiency of excitonic emission, 8 x 10(-5), which indic
ates that the excitonic emission of diamond is a good candidate for applica
tion to semiconductor UV-light-emitting devices. A defect-induced light emi
ssion and large leakage current indicate that a higher UV emission efficien
cy is expected with improvement of the junction quality.