Axial GaN Nanowire‐Based LEDs

Abstract

Axial GaN Nanowire-based LEDs IntroductionCurrent solid state lamps rely on the use of blue light-emitting diodes (LEDs) and the generation of green/red light by phosphor-based down-conversion process. The phosphor-based approach, however, has several fundamental drawbacks, which include a poor color rendition particularly in the red spectral range, significant efficiency loss related to the Stokes shift and phosphor degradation [SCH 05]. In this regard, there is an urgent need to develop high-efficiency GaN-based LEDs in the green and red wavelength range, which has been limited by the lack of suitable substrates, as well as the large lattice mismatch between InN and GaN and the resulting large densities of dislocations and polarization fields for conventional quantum well (QW) LEDs. Moreover, the external quantum efficiency (EQE) of GaN-based QW LEDs generally decreases considerably with increasing injection current. Probable causes for the efficiency droop include defect-assisted carrier leakage [VAM 09], Auger recombination [SHE 07], carrier delocalization [MON 07], inefficient carrier injection related to the presence of internal polarization fields [KIM 07] and the poor hole transport/injection process [XIE 08]. Such critical issues can be addressed, by and large, by utilizing one-dimensional (1D) III-nitride nanowire (NW)/nanorod heterostructures, which can be grown directly on low-cost, large area foreign substrates, and can offer significantly reduced dislocation densities and strain distribution, due to the effective lateral stress relaxation [GLA 06] (for more details, we can refer to Chapter 2 in Vol. 1 [CON 14]). Moreover, such nanoscale structures promise improved light extraction efficiency, due to the large surface-to-volume ratios [HEN 11].III-nitride NW LEDs can be fabricated by using either the top-down or bottomup method. In the last decade, tremendous progress has been made in the epitaxial Chapter written