Nanophotonic crystals on unpolished sapphire substrates for deep-UV light-emitting diodes

Abstract

A new method has been established and employed to create a random nanophotonic crystal (NPhC) structure without photolithography on the unpolished side of a single-side-polished sapphire substrate. This nano structure has potential use in enhancing the light-extraction efficiency (LEE) of deep ultraviolet light-emitting diodes (DUV-LEDs), and has never been built for DUV-LED applications before. Two mask layers in the nano scale (Au and SiO2) were used to create the NPhC and observed using scanning electron microscopy to have an average height of 400 nm and various sizes from 10 to 200 nm. Finally, a conventional DUV-LED and a DUV-LED device with NPhC were simulated using 2D Lumerical Finite-Difference Time-Domain (FDTD) for comparison. The results show that the LEE of the DUV-LED device with this NPhC integrated was significantly directly enhanced by up to 46% and 90% for TE and TM modes, respectively, compared to the conventional DUV-LED device. Thus, this NPhC is believed to be a new, key technique to enhance the LEE of DUV-LEDs.

Visually Hidden, Self-Assembled Porous Polymers for Optical Physically Unclonable Functions

“…To mimic the VSPP, the simulation structure comprises a 3 μm-thick glass and a 4 μm-thick porous PMMA layer. Although the simulation cannot reflect the measurement in real-world scale, the simulation is sufficient to analyze the optical phenomena in VSPP. − The monitored area exhibited a rectangular area of 5 × 5 μm 2 . Figure shows the simulation domain and environment setting.…”

Nanoporous oxide electrodes for energy conversion and storage devices

“…266 The light escape cone refers to the angular range within which light emitted from the LED can escape the device and be effectively emitted into the surroundings. 267 It is determined by the refractive index of the LED materials and the critical angle at which total internal reflection occurs. In a flat sapphire substrate (FSS), if the light reaches an interface at an angle greater than the critical angle, it will be totally internally reflected and unable to escape the LED, as shown in Fig.…”

Enhancing Efficiency of AlGaN Ultraviolet‐B Light‐Emitting Diodes with Graded p‐AlGaN Hole Injection Layer

“…[ 2 ] In addition, the NPhC structure can be applied on the backside of a sapphire substrate. [ 3 ] Moreover, the poor hole transport, insufficient hole carrier concentration, electron overflow, and high nonradiative recombination at a high injection current are the main reasons for the low IQE or IQE droop in the AlGaN UV LED. [ 4,5 ] To improve the IQE, an electron‐blocking layer (EBL) with a high Al composition is inserted between the last barrier and p‐region to suppress the electron leakage.…”