III-Nitride Nanowire Light Sources

In(Ga)N nanowires can be grown catalyst-free on silicon substrates by molecular beam epitaxy with density in the range of 108-1011cm-2 and lengths in the range of a few micrometers depending on the growth time. The nanowires grow vertically in the wurtzite crystalline form and the In composition of the nanowire can be varied to produce emission in the range of 366-700nm. Most importantly, extensive structural characterization by several groups, including ours, indicates that the nanowires are free of extended defects such as dislocations, stacking faults, and twins. It has also been reported that the measured surface recombination velocity in GaN nanowires is very small and ~103cm/s. Temperature dependent luminescence of the nanowires does not exhibit any blue shift, usually attributed to trapping of carriers in localized defects. Due to radial relaxation of strain during epitaxy, the polarization fields in nanowire heterostructures is significantly smaller than those in bulk heterostructures. This reduces the blue shift of the emission peak with injection due to the quantum confined Stark effect. Single or an array of such nanowires can therefore provide an excellent platform for the realization of advanced light sources with unique characteristics. In this talk I will describe the properties of a few such devices being investigated in our group.