Po-Ming Lee

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.

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.