Substrate-Free InGaN/GaN Nanowire Light-Emitting Diodes

Abstract

We report on the demonstration of substrate-free nanowire/polydimethylsiloxane (PDMS) membrane light-emitting diodes (LEDs). Metal-organic vapour-phase epitaxy (MOVPE)-grown InGaN/GaN core-shell nanowires were encapsulated into PDMS layer. After metal deposition to p-GaN, a thick PDMS cap layer was spin-coated and the membrane was manually peeled from the sapphire substrate, flipped upside down onto a steel holder, and transparent indium tin oxide (ITO) contact to n-GaN was deposited. The fabricated LEDs demonstrate rectifying diode characteristics. For the electroluminescence (EL) measurements, the samples were manually bonded using silver paint. The EL spectra measured at different applied voltages demonstrate a blue shift with the current increase. This shift is explained by the current injection into the InGaN areas of the active region with different average indium content.

Keywords: Light-emitting diodes; Nanowire; Substrate-free devices Gallium nitride.

Fig 1

The GaN NW core–shell structure. a Cross-sectional SEM image of the as-grown NWs with the average height of ~20 μm. b 45° tilted SEM image of the NW array. c Top view SEM image of the NWs. d Schematic of the nanowire internal structure

Fig. 2

SEM image of the nanowire/PDMS membrane. Inset shows a high magnification SEM image of the region marked with a black rectangle, where single NWs are visible. The NWs are marked with arrows

Fig. 3

Schematic of the processing steps. a Encapsulated NWs with a metal contact to p-doped GaN shells and a PDMS cap layer before peeling. b Final device consisting of a flipped membrane with a transparent ITO contact to n-doped GaN NW base parts and top metal contact pads. The PDMS cap is partially released, and aluminium foil is attached to the bottom metal contact

Fig. 4

I–V curve of the nanowire/PDMS membrane LED

Fig. 5

EL spectra at 6, 7, and 8 V

Fig. 6

Filtered CL maps of a representative nanowire (a–e)