Core–shell GaN–ZnO moth-eye nanostructure arrays grown on a-SiO2/Si (1 1 1) as a basis for improved InGaN-based photovoltaics and LEDs

https://doi.org/10.1016/j.photonics.2015.03.003Get rights and content

Highlights

  • Non-polar moth-eye GaN was grown by MOVPE on ZnO nanoarray template on Si (1 1 1).

  • ZnO lattice matches to higher indium content InGaN required for PV or green LEDs.

  • Relative reflectance was <1% from 400 to 720 nm at scattering angles <60°.

  • <0.4% reflection <550 nm consistent with graded effective refractive index.

  • Conductive ZnO cores would improve LED & PV current distribution & junction areas.

Abstract

Self-forming, vertically-aligned, ZnO moth-eye-like nanoarrays were grown by catalyst-free pulsed laser deposition on a-SiO2/Si (1 1 1) substrates. X-Ray Diffraction (XRD) and Cathodoluminescence (CL) studies indicated that nanostructures were highly c-axis oriented wurtzite ZnO with strong near band edge emission. The nanostructures were used as templates for the growth of non-polar GaN by metal organic vapor phase epitaxy. XRD, scanning electron microscopy, energy dispersive X-ray microanalysis and CL revealed ZnO encapsulated with GaN, without evidence of ZnO back-etching. XRD showed compressive epitaxial strain in the GaN, which is conducive to stabilization of the higher indium contents required for more efficient green light emitting diode (LED) and photovoltaic (PV) operation. Angular-dependent specular reflection measurements showed a relative reflectance of less than 1% over the wavelength range of 400–720 nm at all angles up to 60°. The superior black-body performance of this moth-eye-like structure would boost LED light extraction and PV anti-reflection performance compared with existing planar or nanowire LED and PV morphologies. The enhancement in core conductivity, provided by the ZnO, would also improve current distribution and increase the effective junction area compared with nanowire devices based solely on GaN.

Section snippets

Acknowledgements

The authors would like to thank the French “Agence Nationale de la Recherche” for financial support and the Centre Technologique Universitaire at the “Institut d’Electronique Fondamentale” of Orsay University for access to the XRD facilities. Acknowledgements to FCT for the funding of RECI/FIS-NAN/0183/2012 (FCOMP-01-0124-FEDER-027494) project is also due.

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