Structural and optical properties of (112̅2) InGaN quantum wells compared to (0001) and (112̅0)

We benchmarked growth, microstructure and photo luminescence (PL) of (11$\bar 2$2) InGaN quantum wells (QWs) against (0001) and (11$\bar 2$0). In incorporation, growth rate and the critical thickness of (11$\bar 2$2) QWs are slightly lower than (0001) QWs, while the In incorporation on (11$\bar 2$0) is reduced by a factor of three. A small step-bunching causes slight fluctuations of the emission wavelength. Transmission electron microscopy as well as atom probe tomography (APT) found very flat interfaces with little In segregation even for 20% In content. APT frequency distribution analysis revealed some deviation from a random InGaN alloy, but not as severe as for (11$\bar 2$0). The slight deviation of (11$\bar 2$2) QWs from an ideal random alloy did not broaden the 300 K PL, the line widths were similar for (11$\bar 2$2) and (0001) while (11$\bar 2$0) QWs were broader. Despite the high structural quality and narrow PL, the integrated PL signal at 300 K was about 4$\times$ lower on (11$\bar 2$2) and more than 10$\times$ lower on (11$\bar 2$0).This work was supported by EU-FP7 ALIGHT No. NMP- 2011-280587 and the UK Engineering and Physical Sciences Research Council No. EP/I012591/1.This is the final version of the article. It first appeared from IOP Publishing via http://dx.doi.org/10.1088/0268-1242/31/8/08500

Core-Shell Nanorods as Ultraviolet Light-Emitting Diodes.

Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core-shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods

Core–Shell Nanorods as Ultraviolet Light-Emitting Diodes

Existing barriers to efficient deep ultraviolet (UV) light-emitting diodes (LEDs) may be reduced or overcome by moving away from conventional planar growth and toward three-dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency, and quantum wells free from the quantum-confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core–shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments, where we find low turn-on voltages, strongly rectifying behaviors and significant electron-beam-induced currents. Time-resolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarization fields. Our results show nanostructuring to be a promising route to deep-UV-emitting LEDs, achievable using commercially compatible methods