Fabrication and chemical lift-off of sub-micron scale III-nitride LED structures

Abstract

Nanoscale light emitting diodes (nanoLEDs, diameter < 1 µm), with active and sacrificial multi-quantum well (MQW) layers epitaxially grown via metal organic chemical vapor deposition, were fabricated and released into solution using a combination of colloidal lithography and photoelectrochemical (PEC) etching of the sacrificial MQW layer. PEC etch conditions were optimized to minimize undercut roughness, and thus limit damage to the active MQW layer. NanoLED emission was blue-shifted ∼10 nm from as-grown (unpatterned) LED material, hinting at strain relaxation in the active InGaN MQW layer. X-ray diffraction also suggests that strain relaxation occurs upon nanopatterning, which likely results in less quantum confined Stark effect. Internal quantum efficiency of the lifted nanoLEDs was estimated at 29% by comparing photoluminescence at 292K and 14K. This work suggests that colloidal lithography, combined with chemical release, could be a viable route to produce solution-processable, high efficiency nanoscale light emitters.

Analysis of the n-GaN electrochemical etching process and its mechanism in oxalic acid

“…Formic acid is known as a strong reductant, and it slowly reacts with oxygen as follows: 44 HCOOH + 0.5O 2 / H 2 O + CO 2aq 44 (13) The IC measurements made at different times aer the experiment qualitatively indicate the scheme of CO 2 transformations before being registered. According to the nitrates found aer the reaction in the liquid phase and the nitrogen gas that appeared on cathode, the side reaction is as follows:…”

“…Generally, III-nitride systems are notable for their high chemical and thermal stability, [1][2][3][4][5] wide tunable bandgap (0.67-6.04 eV) [6][7][8] and the possibility of their nanoscale processing [9][10][11][12] that make them a promising basis for solid-state lighting devices. Recent fabrication technology is a useful option to modify the structure of III-nitride systems to selectively etch excessively ndoped layers either for their complete destruction and li-off of the remaining structure 13,14 or for their porosication. [15][16][17][18] The formation of porous layers may help to improve the properties of III-nitride-based devices in various ways.…”

Designs of InGaN Micro-LED Structure for Improving Quantum Efficiency at Low Current Density

“…These side-wall effects contribute to the Shockley–Read–Hall (SRH) non-radiative recombination, then decrease the quantum efficiency, and become much more serious with a smaller chip size because of the larger specific surface/side-wall area compared with the active region of the device [ 29 – 31 ]. To address this issue, sidewall passivation using dielectric materials and wet etching using buffered hydrofluoric acid or photoelectrochemical method were proposed to minimize these effects to a certain level for the micro-LED [ 31 – 33 ]. However, even improved by the sidewall passivation, the peak EQE of micro-LEDs (with a size smaller than 60 μm) is still lower than 25%, and dramatically decreased to several percent at a current density lower than 2 A cm −2 [ 34 , 35 ].…”

The role of indium composition in InxGa1−xN prestrained layer towards optical characteristics of EBL free GaN/InGaN nanowire LEDs for enhanced luminescence

“…1 In the UV wavelength range, LEDs are used in a broad range of applications, such as water purification, sterilization, chemical and bio-chemical sensing, smart sensor networks, advanced manufacturing, and many more. 1,2 Various works on LEDs have been reported, such as InGaN LEDs used in an optical link, 3 parallel flip-chip AlGaN LED whose electrical and optical characteristics display strong size dependence for communication in the UV range, 4 and introduction of light-emitting commutating diodes (LECDs). 5 III-nitride materials are capable of manufacturing lasers and LEDs, 6,7 but it is still difficult to get high efficiency GaN/InGaN LED.…”

“…Group III‐nitride ultraviolet (UV) light emitting diodes (LEDs) have attained remarkable attention as a suitable and eco‐friendly light source for various applications, such as pharmaceutical applications, water and air purification, surface disinfection, displays, and so forth 1 . In the UV wavelength range, LEDs are used in a broad range of applications, such as water purification, sterilization, chemical and bio‐chemical sensing, smart sensor networks, advanced manufacturing, and many more 1,2 . Various works on LEDs have been reported, such as InGaN LEDs used in an optical link, 3 parallel flip‐chip AlGaN LED whose electrical and optical characteristics display strong size dependence for communication in the UV range, 4 and introduction of light‐emitting commutating diodes (LECDs) 5 .…”