Ultralow threshold electrically injected AlGaN nanowire ultraviolet lasers on Si

Ultraviolet (UV) lasers are of paramount importance for applications in water purification, diagnosis and bio-agent detection. Here we report that, with the use of dislocation-free AlGaN nanowires formed directly on Si substrate, electrically injected UV emission in the wavelength range from 319 nm to 335 nm can be readily achieved, which is the shortest wavelength range ever reported for electrically injected semiconductor lasers. In this work, catalyst-free AlGaN nanowire arrays are grown directly on Si substrate by radio frequency plasma-assisted molecular beam epitaxy (MBE). Our detailed calculation shows that such vertically aligned randomly distributed sub-wavelength scale nanowire array can sustain random lasing action. Various lasing peaks from 319 nm to 335 nm can be measured from such AlGaN nanowire samples under electrical injection. The threshold is measured to be in the range of tens of A/cm2 at cryogenic temperature, which is significantly smaller than the commonly reported GaN-based quantum well lasers. The measured linewidth is as narrow as 0.2 nm.