Local nanotip arrays sculptured by atomic force microscopy to enhance the light-output efficiency of GaN-based light-emitting diode structures

Abstract

In this work, local nanotip arrays on GaN-based light-emitting (LED) structures were fabricated through nano-oxidation using an atomic force microscope (AFM). The photoluminescence (PL) intensity of the InGaN/GaN multiple quantum wells (MQWs) active layer and the light extraction efficiency of the LED structure were enhanced by forming this nanotips structure to serve as a graded-refractive index layer, which is further validated by the finite-difference time-domain analysis. The PL emission peak of the MQWs active layer has a blue-shift phenomenon that is caused by a partial reduction of the strain on the InGaN well. It is expected that our approach opens a promising route for simultaneously enhancing both the internal quantum efficiency and the light extraction efficiency of GaN-based LEDs. The proposed AFM-based method will be of importance for local patterning the light emitting components for optoelectronic applications.

Advanced oxidation scanning probe lithography

“…Figure 6 illustrates some of the nanopatterning capabilities of o-SPL. Silicon oxide line arrays with a periodicity of 15 nm (7.5 nm half pitch) have been patterned on Si( 100 Other examples to tailor functional surfaces at the nanoscale are illustrated by the change in the work function of silver nanoparticle sheets to tune the plasmonic properties [86], the tunability of the surface adhesion by patterning different geometric shape arrays on a GaAs substrate [87] or the fabrication of GaO x nanotips on the surface of a GaNbased light emitting diode to improve the light extraction efficiency [88].…”

Monolithic integration of GaN-based light-emitting diodes and metal-oxide-semiconductor field-effect transistors

“…The LED layerstructure comprised of a 30-nm-thick GaN nucleation layer grown at 520°C, a 2-μm-thick undoped GaN layer grown at 1050°C, 2-μm-thick Si-doped n-type (n = 5 × 10 18 cm −3 ) GaN cladding layer grown at 1050°C, an unintentionally doped active region of five periods InGaN/GaN MQWs grown at 700 °C with emitting wavelength of λ = 485 nm, and a 200nm-thick Mg-doped p-type (p = 3 × 10 17 cm −3 ) GaN layer grown at 800°C. The low growth temperature of p-type GaN layer is to roughen its surface for enhanced light extraction efficiency of the LED [21][22][23]. The LED structure was then selectively removed by dry etching (inductively coupled plasma, ICP) with Ar/Cl 2 mixed gases to expose the n-type GaN layer for the subsequent fabrication of MOSFET.…”

Analysis of degradation mechanisms in GaN-based light-emitting diodes under reverse-bias stress: effects of defects and junction-temperature increase

“…However, since it is not easy to find the cause of defect-related performance degradation just from the basic characteristics mentioned above, additional analysis techniques are required. On the other hand, the changes in microscopic structures and their effects on the basic characteristics are attempted by introducing various spectroscopic and/or microscopic techniques such as admittance spectroscopy, 4) deep-level transient spectroscopy, 5) noise measurements, 6) the photoemission microscopy (PHEMOS), 7) applied voltage or current mapping, 8) cathodoluminescence, 9) photoluminescence, 10) the transmission electron microscopy, 11) atomic-force microscopy, 12) and the near-field scanning optical microscopy. 13) There exist published works on the reliability and performance of GaN-based LEDs based on the measurement results mentioned above, which suggest the following causes: generation/propagation of defects in the active multiple-quantum-well (MQW) region with a subsequent decrease in light output power; [14][15][16] impurities interacting with acceptor dopants and migration of metal atoms along the defect tubes, leading to changes in semiconductor resistivity; [17][18][19] self-heating due to the current crowding, a narrow thermal path to the heat-sink, and decreased external quantum efficiency elevating the junction temperature with the overall performance degradation.…”