Takaharu Tashiro

Microstructural and topographical changes of Ni-P plated moulds in glass lens pressing

The changes in microstructure and topography of nickel-phosphorus (Ni-P) plated steel moulds in a glass lens moulding process were investigated by heating tests. The results show that, at a high temperature, Ni atoms diffuse from the inner Ni-P plating layer into the outer release agent coating consisting of precious metals. The atomic diffusion leads to partial surface swelling, which makes the mould surface rough and cloudy. The diffusion is influenced by the temperature, interface structure and stress state of the moulds. These findings provide references for developing new mould materials and for improving the service life of the moulds.

High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer

We increased the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) by introducing a highly reflective photonic crystal (HR-PhC) into the surface of the p-AlGaN contact layer, thereby achieving a high external quantum efficiency (EQE). A low-damage HR-PhC with a lattice period of approximately 250 nm was fabricated using nanoimprinting and dry etching. A reflective Ni/Mg p-type electrode was deposited on the HR-PhC layer using a tilted-evaporation method. The EQE of a conventional DUV LED with emission around 283 nm was increased from 4.8 to 10% by introducing the HR-PhC and the reflective Ni/Mg electrode. A simple estimation of the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode indicated a value exceeding 90%.