High-Quality A1GaN Epitaxy on Lattice-Engineerable AlN Template for High-Power UVC Light-Emitting Diodes

AlGaN-based UVC light-emitting diodes (LED) were fabricated on high-quality AlN templates with an engineerable in-plane lattice constant. The controllability of the in-plane strain originated from the vacancy formation in Si-doped AlN (AlN:Si) and their interaction with edge dislocations. The strain state of the AlN:Si top interface could be well depicted by a dislocation-tilt model depending on the buffer strain state, threading dislocation density (TDD), and regrown AlN:Si thickness. The validity of the model was verified by cross-sectional TEM analysis. With a gradually widened lattice constant of regrown AlN:Si layer, strain-induced defects of subsequently grown n-AlGaN was suppressed. Therefore, growing a current spreading layer which possesses a moderate Al content (<65%), decent thickness (>1.5 μm), and a low TDD (<1.0×10 9 cm -2 ) simultaneously becomes possible. Additionally, the idea of an optimal edge TDD ) in the AlN buffer was revealed for growing high-quality n-AlGaN layers with a targeted thickness. After a deliberate strain-TDD engineering for AlN:Si and n-AlGaN, high-power UVC LEDs (P>200 mW) with a low forward voltage (V f =5.7 volt) were demonstrated at I=1.35 A. The low forward voltage under high current injection density was attributed to the success in preparation of a low series resistance and high-quality n-AlGaN current spreading layer.