Toward Discrete Axial p–n Junction Nanowire Light-Emitting Diodes Grown by Plasma-Assisted Molecular Beam Epitaxy

In this paper we investigate axial p – n junction GaN nanowires grown by plasma-assisted molecular beam epitaxy (MBE), with particular attention to the effect of Mg doping on the device characteristics of individual nanowire light-emitting diodes (LEDs). We observe that a significant fraction of single-nanowire LEDs produce measurable band-gap electroluminescence when a thin AlGaN electron blocking layer (EBL) is incorporated into the device structure near the junction. Similar devices with no EBL typically yield below-detection-limit electroluminescence, despite diode-like I – V characteristics and optically measured internal quantum efficiencies (IQEs) of ∼1%. I – V measurements of the p -regions in p – n junction nanowires, as well as nanowires doped with Mg only, indicate low p -type conductivity and asymmetric Schottky-like p -contacts. These observations suggest that imbalanced carrier injection from the junction and p -contact can produce significant nonradiative losses.