Red-Emitting ( nm) In0.51Ga0.49N/GaN Disk-in-Nanowire Light Emitting Diodes on Silicon

We have investigated the properties of In_0.51Ga_0.49N/GaN disk-in-nanowire light emitting diodes (LEDs) epitaxially grown on silicon substrates by plasma-assisted molecular beam epitaxy. The radiative efficiency of the nanowire ensemble, obtained from the temperature-dependent photoluminescence measurements, under optimized growth conditions is 43%, which increases to 55% after parylene passivation. From high resolution transmission electron microscopy, it is evident that there is significant coalescence between nanowires when the areal density approaches 10¹¹ cm^-2. We have identified and characterized deep level electron and hole traps in the GaN nanowires and it is found that the trap densities increase with nanowire density, or with the degree of coalescence. It is therefore believed that the deep levels originate from dislocations and stacking faults arising from nanowire coalescence. The best output characteristics are measured in a LED having a nanowire density of 2 × 10¹⁰ cm^-2, which exhibits a maximum internal quantum efficiency of ~55% at an injection level of 10 A/cm². It is seen that the maximum efficiency would increase to 60% in the absence of deep level traps.