Electrically pumped ultraviolet lasing from ZnO in metal-insulator-semi devices

Electrically pumped ultraviolet random lasing was achieved in metal-insulator-semiconductor (MIS) diodes based on ZnO films at room temperature. The ZnO films were grown by plasma assisted molecular beam epitaxy. Two different kinds of insulator layers, SiO (x) (0 < xa parts per thousand currency sign2) and AlO (x) (0 < xa parts per thousand currency sign1.5) were deposited by electron beam evaporation. X-ray diffraction experiments found these oxide layers were amorphous (or microcrystals), and X-ray photoelectron spectroscopy confirmed the Si and Al were fully oxidized. Compared with devices using SiO (x) as the insulator layer, diodes with evaporated AlO (x) layers showed a lower working threshold forward current (similar to 20 mA to similar to 26 mA) and higher emission intensity. Periodic features indicating formation of closed-loop paths were deduced by the power Fourier transform of electroluminescence spectra. The cavity length of both devices increased as forward currents increased, while a larger cavity length was always obtained in the AlO (x) -involved device under the same working current. The improved performance was attributed to larger hole amount in AlO (x) layers. These results revealed that evaporated AlO (x) can serve as good electron blocking and hole supplying layers for hetero-structures.