The growth and optical properties of GaN nanorods grown by plasma-assisted molecular beam epitaxy are investigated as a function of growth temperature with and without the presence of an AlN buffer. When grown on bare Si(111), an increase in the growth temperature leads to a reduction in nanorod diameter and an increase in density. The diffusion-induced mechanism has a greater impact on enhancing the growth of nanorods on the AlN buffer surface as compared to that on bare Si(111). The GaN nanorod density is influenced by the presence of the AlN buffer and can be controlled by varying the growth temperature. The low density of 6.23x10(9) cm(-2) of GaN nanorods is achieved without altering the nanorod size.