Controlled Coalescence of AlGaN Nanowire Arrays: An Architecture for Nearly Dislocation‐Free Planar Ultraviolet Photonic Device Applications

Abstract

Nearly dislocation-free semipolar AlGaN templates are achieved on c-plane sapphire substrate through controlled nanowire coalescence by selective-area epitaxy. The coalesced Mg-doped AlGaN layers exhibit superior charge-carrier-transport properties. Semipolar-AlGaN ultraviolet light-emitting diodes demonstrate excellent performance. This work establishes the use of engineered nanowire structures as a viable architecture to achieve large-area, dislocation-free planar photonic and electronic devices.

Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy

“…Figure 1b shows a scanning electron microscopy (SEM) image of GaN nanowires grown by selective area epitaxy [55]. It is seen that nanowires with the same height, diameter, and spacing are grown.…”

“…Besides the excellent control of the nanowire formation site and size uniformity, using selective area epitaxy can lead to nearly defect-free, quasi-epilayer template with arbitrary alloy composition, through a controlled coalescence process. For example, AlGaN quasi-epilayer templates have been obtained through coalescing AlGaN nanowires grown by selective area epitaxy on Ti-patterned GaN template [55]. This could open up an important approach to grow nearly defect-free III-nitride device layers on lattice matched template.…”

“…In this approach, a mask layer, e.g., SiO x , SiN x , or Ti, is first deposited on substrates such as a Si or GaN template, followed by e-beam lithography to create nano-sized openings, as illustrated in Figure 1a [55].…”

“…Crystals 2017, 7, 268 3 of 17 [55]. Due to different atom kinetics on the surface of the mask layer and substrate, the nucleation process takes place preferentially in the openings [55][56][57][58][59][60][61][62][63][64][65][66].…”

Thermodynamic photoinduced disorder in AlGaN nanowires

“…[6][7][8] Using a variety of growth techniques, 9,10 AlN and its alloys Al x Ga 1x N (0 < x ≤ 1) are expected to facilitate the fabrication of more sensitive UV photodetector devices, 11,12 ultralow-threshold UV lasers, 13 and reduce polarization fields. 14,15 GaN-based nanowire devices have high quantum efficiencies, 16,17 sharp peaks of density of states at the lowest quantized sub-band energy levels, 18 improved exciton binding energy, 19 and increased wavefunction overlap of the electron-hole pairs. 20 Moreover, designing heterojunctionbased optoelectronic devices through the integration of three-dimensional (3D) group-III-nitride 25 They argued that the p-type conduction is dominated by hopping conduction.…”