Nanoscale imaging of reduced forward bias at V-defects in green-emitting nitride LEDs

TL;DR

This study uses nanoscale imaging to reveal that V-defects in green-emitting nitride LEDs facilitate reduced forward bias and charge injection, explaining their improved efficiency.

Contribution

It introduces a novel scanning tunneling luminescence approach to directly observe charge injection at V-defects in LEDs, confirming the mechanism behind efficiency improvements.

Findings

V-defects reduce forward bias by about 1 V

Charge injection occurs more easily at V-defect rims

Electroluminescence shows small blue shifts near V-defects

Abstract

Record wall-plug efficiencies in long-wavelength, III-nitride light-emitting diodes (LEDs) have recently been achieved through improvements in electrical efficiency in devices containing V-defects. Numerical modeling suggests this may be due to reduced barrier heights for charge injection in thinned, low-Indium quantum wells parallel to semi-polar V-defect facets. To test this proposition, a novel approach in which the tip of a scanning tunneling luminescence microscope as a local hole injector, is used to map the optoelectronic properties of commercial, green-emitting LED heterostructures around V-defects with nanoscale spatial resolution. A 1 V reduction in the forward bias necessary for current injection at V-defect rims is observed. This, combined with the observation of small (~10 meV) blue shifts in the locally emitted electroluminescence, unambiguously confirms the charge injection mechanism.