Efficient Deep Ultraviolet Emission from Self-Organized AlGaN Quantum Wire Array Grown On Ultrathin Step-bunched AlN Templates

The achievement of high-efficiency AlGaN-based deep ultraviolet (DUV) emitters is greatly limited by the poor crystalline quality and negligible carrier localization effect of the Al-rich AlGaN quantum structures. Herein, we propose solving this long-standing issue via surface engineering. By changing the misorientations of sapphire substrates, Al(Ga)N epilayers obtained different step heights and shapes. Accordingly, surface-mediated dislocation climbing and surface adatom incorporation behaviors can be well regulated. Profiting from macrostep-mediated dislocation climbing behavior, dislocation inclination and interaction become more frequent. Thus, for the 1 mu m-thick AlN epilayers grown on C/A-4(degrees) and C/M-4(degrees) sapphire substrates, only a few mixed-type dislocations are found. However, this process also continuously induces tensile stress. To alleviate tensile stress and pursue efficient DUV emission, we constructed nominal quantum wells on 400 nm ultrathin step-bunched AlN epilayers. Interestingly, the different incorporation behaviors of Al and Ga adatoms induce the formation of quantum wells at the macrostep terraces and quantum wires at the macrostep edges, respectively. The excellent crystalline quality of the AlN/sapphire templates and the dominant luminescence of the high-density self-organized quantum wire array lead to a high internal quantum efficiency of 70%. This work paves the way for achieving high-efficiency devices on a low-cost ultrathin platform.