Impacts of dislocations and point defects on the internal quantum efficiency of the near-band-edge emission in ALGaN-based DUV light-emitting materials

Abstract

In this chapter, we show the impact of point defects rather than threading dislocations (TDs) on the emission dynamics of the near-band-edge (NBE) excitonic luminescence in AlN and high AlN mole fraction (x) AlxGa1−xN alloy films using deep ultraviolet (DUV) time-resolved luminescence and positron annihilation measurements. The extreme radiative nature of excitons in AlN is identified, as the radiative lifetime (τR) for a free excitonic emission was determined to be as short as 11 ps at 7 K and 180 ps at 300 K, which are the shortest ever reported for the spontaneous emission in bulk semiconductors. However, apparent τR increased to 530 ps at 7 K with increasing impurity and Al-vacancy (VAl) concentrations irrespective of the TD density. The result reflects the contribution of bound exciton components. A continuous decrease in τR with increasing temperature up to 200 K of heavily impurity-doped samples reflects a carrier release from band-tail states. The room temperature (RT) τR of AlxGa1−xN alloys of high x was nevertheless as short as a few ns at 300 K. The results essentially indicate an excellent radiative performance. Finally, the impact of Si-doping and the resulting cation vacancy formation on the nonradiative lifetime (τNR) of the NBE emission in Al0.6Ga0.4N films are discussed.