Abstract
The growth of self-assembled, vertically oriented and uniform nanowires (NWs) has remained a challenge for efficient light-emitting devices. Here, we demonstrate dislocation-free AlGaN NWs with spontaneous coalescence, which are grown by plasma-assisted molecular beam epitaxy on an n-type doped silicon (100) substrate. A high density of NWs (filling factor > 95%) was achieved under optimized growth conditions, enabling device fabrication without planarization using ultraviolet (UV)-absorbing polymer materials. UV-B (280-320 nm) light-emitting diodes (LEDs), which emit at similar to 303 nm with a narrow full width at half maximum (FWHM) (similar to 20 nm) of the emission spectrum, are demonstrated using a large active region ("active region/NW length-ratio" similar to 50%) embedded with 15 stacks of AlxGa1-xN/AlyGa1-yN quantum-disks (Qdisks). To improve the carrier injection, a graded layer is introduced at the AlGaN/GaN interfaces on both p-and n-type regions. This work demonstrates a viable approach to easily fabricate ultra-thin, efficient UV optoelectronic devices on low-cost and scalable silicon substrates.