Submicrometre resolved optical characterization of green nanowire-based light emittingdiodes

Abstract

The electroluminescent properties of InGaN/GaN nanowire-based light emitting diodes(LEDs) are studied at different resolution scales. Axial one-dimensional heterostructureswere grown by plasma-assisted molecular beam epitaxy (PAMBE) directly on a silicon(111) substrate and consist of the following sequentially deposited layers: n-type GaN,three undoped InGaN/GaN quantum wells, p-type AlGaN electron blocking layer andp-type GaN. From the macroscopic point of view, the devices emit light in the greenspectral range (around 550 nm) under electrical injection. At 100 mA DC current, a1 mm2 chip thatintegrates around 107 nanowires emits an output power on the order of10 µW. However, the emission of the nanowire-based LED shows a spotty andpolychromatic emission. By using a confocal microscope, we have been ableto improve the spatial resolution of the optical characterizations down tothe submicrometre scale that can be assessed to a single nanowire. Detailedμ-electroluminescent characterization (emission wavelength and output power)over a representative number of single nanowires provides new insights intothe vertically integrated nanowire-based LED operation. By combining bothμ-electroluminescentand μ-photoluminescent excitation, we have experimentally shown that electrical injectionfailure is the major source of losses in these nanowire-based LEDs.