Abstract
In this study, the selective area growth (SAG) of high-density (2.5×109 cm-2) GaN nanowires (NWs) embedded with Ga(In)N quantum boxes (QBs) on Si(111) substrate by plasma-assisted molecular beam epitaxy are demonstrated. At first, substrates with various masking materials are prepared for SAG GaN growth: TiN nanoholes and AlN nanopedestal array are chosen as SAG substrates for their ideal NW growth selectivity. However, TiN nanoholes failed to provide adequate NW growth selectivity due to titled NWs while growing on Si surface. Thus, AlN seeding layers are used in this study. Next, effects of morphology and thickness of the AlN seeding layer on the quality of SAG GaN NWs are investigated. A thin and smooth AlN seeding layer without forming Al droplets on the surface is achieved by grading the Al flux and growth temperature from low to high during the growth. High-density AlN nanopedestal arrays used as seeds for SAG GaN NWs are fabricated from thin AlN seeding layers using the soft nanoimprint lithography. By adjusting the growth temperature and Ga/N flux ratio, hexagonal shaped SAG GaN NWs are realized. The quality of SAG GaN NWs is evaluated using low temperature photoluminescence (PL) measurements. Three major PL peaks at 3.47, 3.45, and 3.41 eV are detected and identified. The peak at 3.471 eV is related to the neutral donor-bound exciton emission, and the 3.41 eV broadband emission is attributed to stacking faults or structural defects. The 3.45 eV peak is identified as the emission due to exciton recombination at polar inversion domain boundaries of NWs. Finally, Ga(In)N QBs embedded in GaN NWs are grown. The full visible spectrum emission can be realized by tuning In contents of QBs through varying growth temperature of Ga(In)N layers.