UV-visible broad spectrum light emitting device of ZnO/MgO/ITO structure

Xenon gas and mercury vapor based broad spectrum light sources have wide application, however, are hard to compact. On the contrary, LEDs are easy for compaction, but are hard to emit a broad spectrum. In this work, we demonstrate a simple phosphor free LED structure of ZnO/MgO/ITO, of which the spectrum covers the range from 300 to 650 nm. The device was fabricated on commercially available ITO substrate, and the ZnO/MgO structure was successively grown by MOCVD method, of which the morphology, crystallinity and optical quality were characterized. A thin MgZnO layer with graded composition is believed to form through the miscibility of MgO and ZnO during the initial growth stage of ZnO. The active region of the device includes the thin MgZnO layer and part of the subsequent grown ZnO layer. The light with wavelength shorter than ~360 nm is attributed to the near band edge emission of the MgZnO layer. And the near band edge emission and deep level emissions of ZnO contribute to the spectrum from ~360 to 650 nm. The working mechanism of the device is discussed mainly based on the energy band diagram.