Sheet Charge Engineering Towards An Efficient Hole Injection In 290 Nm Deep Ultraviolet Light-Emitting Diodes

The hole injection efficiency is one of the bottlenecks that restrict the external quantum efficiency (EQE) and optical power of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). The polarization-induced positive sheet charges at the last quantum barrier (LQB)/electron blocking layer (EBL) interface reflect the holes back to the p-type layer and weaken the hole injection capability into the active region. In this work, we designed and incorporated a polarization-engineered AlxGa1-xN/AlyGa1-yN superlattice layer at the LQB/EBL interface. The positive sheet charges at the LQB/EBL interface can be inverted into negative charges with optimal Al compositions in the AlxGa1-xN/AlyGa1-yN superlattice layer. The electron confinement and hole injection efficiency can also be improved through increasing the effective barrier height for electrons and decreasing the effective barrier height for holes, resulting in an enhanced optical power by 29.4% and alleviated efficiency droop by 78.4% for the proposed device with an Al0.67Ga0.33N/Al0.7Ga0.3N superlattice insertion layer. The sheet charge engineering method by polarization provides an alternative approach to boost the hole injection efficiency towards an enhanced device performance for DUV LEDs.