Zlatko Sitar

Materials Science and Engineering, North Carolina State University, USA

Despite the rapid progress in III-nitride-based laser diodes, sub-300 nm UV semiconductor lasers have not been realized mainly due to technical and scientific barriers arising from the lack of proper crystalline substrates and poor understanding of point defect control in wide bandgap semiconductors. While doping is (almost) trivial in classical semiconductors (Si, Ge, GaAs), it becomes increasingly more challenging as the bandgap widens. Excess available energy drives the incorporation of unwanted impurities and generation of native point defects, which act as compensators, resulting in high resistivity and low mobilities. Based on current understanding of point defect energetics, we developed a Fermi level control scheme that suppresses compensation during growth and enables effective n- and p-doping. This point defect control scheme uses photo-generated charge carriers to control the electro-chemical potential of the system and the formation energy of charged point defects.

This point defect control scheme led to devices with much higher efficiency and has a potential to enable the exploitation of AlGaN alloys over the whole composition range (bandgap of 3.4-6.1 eV). These developments have recently resulted in the first demonstration of lasing from a semiconductor at 260 nm.