Yen-Shuo Liu

Light Extraction Enhancement of Vertical LED by Growing ZnO Nano-Rods on Tips of Pyramids

Creating a pyramidal structure on an n-GaN surface is considered the most effective approach for maximizing light extraction of n-side-up GaN-based light-emitting diodes (LEDs). This letter shows that the light extraction efficiency of a pyramidal n-GaN surface can be further enhanced by growing ZnO nano-rods (NRs) specifically on the tips of the pyramids on the n-GaN surface. Using tip-only ZnO NRs, the light-output power of an n-side-up LED with a pyramidal n-GaN surface can be further enhanced by 49.6% at 250 mA. This improved light extraction efficiency is due to the multiple facets on the ZnO NRs.

Preparation of V-doped AZO thin films and ZnO nanorods on V-doped AZO thin films by hydrothermal process

The growth mechanisms of ZnO nanorods (NRs) on sputtered Al-doped ZnO (AZO) and V-doped AZO (V:AZO) thin films are studied in this work. Firstly, the microstructure of the AZO and V:AZO thin films was investigated by XRD. We found that V-dopants retard the crystallization (grain growth) and enlarge the d-spacing of the (0002) plane of the V:AZO thin films. ZnO NRs were prepared on the AZO and V:AZO thin film substrates by the hydrothermal method. Vertically aligned ZnO NRs were grown on the pure AZO thin film substrate. With incorporating V-dopants, the growth direction of ZnO NRs grown on the V:AZO thin films is highly influenced by the concentration of the V-doping. The V-doping causes the random growth direction of ZnO NRs. XRD and SEM analysis indicate that the growth behavior of ZnO NRs depends on the microstructure of the surface grains of the AZO and V:AZO thin film substrates. A growth mechanism of ZnO NRs on the AZO and V:AZO thin film substrates is proposed in this work.

Light-Extraction Enhancement by Cavity Array-Textured N-Polar GaN Surfaces Ablated Using a KrF Laser

The creation of KOH-etched pyramidal patterns on the N-GaN surface is considered to be the most effective texturing method for improving the light-extraction efficiency of GaN LEDs. Using KrF-laser ablation, concave downward cavities are formed on the N-GaN surface. This letter demonstrates that KrF-laser-ablated cavities enhance the light-extraction efficiency of the KOH-etched pyramidal N-GaN surface by 25%. With further etching by KOH, the curved-surface sidewall of laser-ablated cavities do not form pyramids; instead, relatively large inclined facet sidewalls are formed in the laser-ablated cavities. We believe that these inclined facet sidewalls in laser-ablated cavities further enhance the light-extraction efficiency of KOH-etched pyramidal N-GaN surfaces.

Nanomeshed Pt(Au) Transparent Contact to p -GaNof Light-Emitting Diode

This study examines nanomeshed Pt and Pt(Au) thin films formed by a dewetting process on a p-GaN surface. With prolonged annealing, the Pt(Au) layer shows more stable contact resistance to p-GaN and lower sheet resistance than the Pt layer. L–I curves show that the GaN light-emitting diode (LED) with the Pt(Au) transparent conducting layer (TCL) produces more light output power than the GaN LED with the Pt TCL. The higher light output of the LED with the Pt(Au) TCL is attributed to the lower sheet resistance, which improves current spreading in the active region.

Transparent p-AlN:SnO2/n-SnO2 tunnel diode

Using the diffusivity discrepancy between Al and N in the SnO2 phase, N-doped n+ and Al-doped p+ degenerate regions were created at the interface by annealing an AlN/SnO2 bilayer. Current–voltage (I–V) characteristics of the p+-AlN:SnO2/n+-SnO2 junction indicate distinct tunnel diode characteristics, such as the tunneling mode, negative differential resistance, and turn-on mode. The overall transmittance of the p-AlN:SnO2/n-SnO2 tunnel diode is higher than 80% in the visible region. In a certain wavelength region, the transmittance of the p-AlN:SnO2/n-SnO2 tunnel diode is even higher than 90%. This shows that a transparent p-AlN:SnO2/n-SnO2 tunnel diode has great potential for use in a broad range of invisible electronics.