Abstract
The integration of GaN-based light-emitting diodes (LEDs) onto flexible platforms provides opportunities for conformal lighting, wearable electronics, and bendable displays. While this technology may enhance the functionality of the light source, the development of flexible GaN LEDs suffers from performance degradation, when mechanical bending is applied during operation. A unique approach to eliminate the degradation employs dot-in-wire structures, using cylindrical light-emitting heterostructures that protrude above the flexible platform, separating the active light-emitting region from the bending substrate. Here, we demonstrate the optical enhancement of nanowire light emitters by changing the geometric orientation within a 1 × 1 mm2 array of nanowires on a flexible platform through bending of the substrate platform. The flexible structures were achieved by transferring GaN nanowire LEDs from sapphire substrates onto flexible polyethylene terephthalate (PET) using a “paste-and-cut” integration process. The I–V characteristics of the nanowire LEDs showed negligible change after integration onto the PET, with a turn-on voltage of 2.5 V and a forward current of 400 μA at 4 V. A significant advantage for the nanowire devices on PET was demonstrated by tilting the LEDs through substrate bending that increased the electroluminescence (EL) intensity, while the I–V characteristics and the EL peak position remained constant. Through finite-element analysis and three-dimensional finite-difference time-domain modeling, it was determined that tilting the protruding devices changed the effective distance between the structures, enhancing their electromagnetic coupling to increase light output without affecting the electrical properties or peak emission wavelength of the LEDs.
Highlights
GaN-based “dot-in-nanowire” light-emitting diodes (LEDs), cylindrical devices that mimic a quantum dot within a nanowire (NW) structure, are an emerging technology for phosphor-free whitelighting applications and ultraviolet light emitters.[1,2] The emission from an array of LEDs, having a typical diameter of ~250 nm, is dependent on waveguide modes coupled through the geometry of the cylinder and the distance between neighboring devices
The finite-element analysis (FEA) model, based on actual structures grown by plasma-assisted molecular-beam epitaxy (PAMBE), consisted of cylindrical nanostructures having
Published in partnership with Nanjing Tech University diameters of ~250-nm, separated by a 350-nm pitch positioned on degrade the I–V characteristics and EL peak position of the light a 3-μm-thick GaN film in contact with a 1-μm-thick metallic electrode bonded to a 175-μm-thick flexible polyethylene terephthalate (PET) substrate
Summary
GaN-based “dot-in-nanowire” light-emitting diodes (LEDs), cylindrical devices that mimic a quantum dot within a nanowire (NW) structure, are an emerging technology for phosphor-free whitelighting applications and ultraviolet light emitters.[1,2] The emission from an array of LEDs, having a typical diameter of ~250 nm, is dependent on waveguide modes coupled through the geometry of the cylinder and the distance between neighboring devices. While creating a flexible assembly, the encapsulation of the LEDs within the elastomer limits the motion of the NWs, and the LEDs would experience mechanical strain within the active region of the device during substrate bending. These initial reports did not characterize the current–voltage (I–V) behavior of the flexible NW LEDs under mechanical strain, and the effect of substrate bending on the NW LED light-output characteristics, is not well understood
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