Morphology and optical properties of Mg doped GaN nanowires in dependence of growth temperature

摘要

The influence of the substrate temperature and Mg doping on the morphological and optical properties of catalyst-free GaN nanowires grown by plasma-assisted molecular beam epitaxy on Si(111) has been investigated in a large temperature range between 665°C and 785°C. The density and wire sizes in Mg-doped nanowires are found to change with substrate temperature in a similar way as undoped nanowires. Between 725 °C and 785 °C a trimodal size distribution and an increase of the wire density from 5.0×10 ~9 cm~(-2) to 9.5×10~9 cm~(-2) were observed. Transmission electron microscopy indicates that the upper parts of the nanowires are free of structural defects. Raman spectroscopy measurements confirm a high crystalline quality of doped wires, with a line width of the E_2~H of 3.3 cm~(-1) for samples grown at T _s=785 °C. Photoluminescence measurements show a strong influence of Mg on the emission properties, namely the increase of the donor-acceptor pair emission and its phonon replicas.