Ultralow-threshold laser realized in zinc oxide

A study was conducted to demonstrate engineered band alignment of n-Zn and p-GaN heterojunctions using a dielectric MgO layer, to obtain continuous-current-driven lasers in ZnO. The threshold current of the laser was 0.8 mA, the smallest to be reported for blue- and ultraviolet-light semiconductor laser diodes. It was found that the layer was composed of closely packed quasi-hexagon-shaped columns with average size of about 100 nm. The spectrum of ZnO displayed a dominant sharp nearband-edge (NBE) emission at 378nm and a significantly weak deep-level emission at around 550 nm. It was found that the spectrum of the p-GaN was dominated by a broad peak centered at about 450 nm, which was observed in Mg-doped p-GaN and contributed to transitions between conduction-band electrons or donors and Mg-related acceptors.