Correlation between the structural and optical properties of spontaneously formed GaN nanowires: a quantitative evaluation of the impact of nanowire coalescence

摘要

We investigate the structural and optical properties of spontaneously formedGaN nanowires with different degrees of coalescence. This quantity isdetermined by an analysis of the cross-sectional area and perimeter of thenanowires obtained by plan-view scanning electron microscopy. X-ray diffractionexperiments are used to measure the inhomogeneous strain in the nanowireensembles as well as the orientational distribution of the nanowires. Thecomparison of the results obtained for GaN nanowire ensembles prepared on bareSi(111) and AlN buffered 6H-SiC(000-1) reveals that the main source of theinhomogeneous strain is the random distortions caused by the coalescence ofadjacent nanowires. The magnitude of the strain inhomogeneity induced bynanowire coalescence is found not to be determined solely by the coalescencedegree, but also by the mutual misorientation of the coalesced nanowires. Thelinewidth of the donor-bound exciton transition in photoluminescence spectradoes not exhibit a monotonic increase with the coalescence degree. In contrast,the comparison of the root mean square strain with the linewidth of thedonor-bound exciton transition reveals a clear correlation: the higher thestrain inhomogeneity, the larger the linewidth.