Shuji Shioji

InGaN-Based Near-Ultraviolet and Blue-Light-Emitting Diodes with High External Quantum Efficiency Using a Patterned Sapphire Substrate and a Mesh Electrode

We markedly improved the extraction efficiency of emission light from the InGaN-based light-emitting diode (LED) chips grown on sapphire substrates. Two new techniques were adopted in the fabrication of these LEDs. One is to grow nitride films on the patterned sapphire substrate (PSS) in order to scatter emission light. Another is to use the Rh mesh electrode for p-GaN contact instead of Ni/Au translucent electrode in order to reduce the optical absorption by the p-contact electrode. We fabricated near-ultraviolet (n-UV) and blue LEDs using the above-mentioned techniques. When the n-UV (400 nm) LED was operated at a forward current of 20 mA at room temperature, the output power and the external quantum efficiency were estimated to be 22.0 mW and 35.5%, respectively. When the blue (460 nm) LED was operated at a forward current of 20 mA at room temperature, the output power and the external quantum efficiency were estimated to be 18.8 mW and 34.9%, respectively.

Highly Reliable and Highly Reflective Ag Metallizing of a Sapphire Surface of an LED Die

Previously, we reported the introduction of the low-temperature, pressure-less Ag direct bonding method, which has a high bond strength. In spite of this, when Ag was deposited directly on the sapphire surface of a GaN-based light-emitting diode die as a reflective layer, there were still some remaining problems with unreliable adhesion. Hence, this paper focuses on improving adhesion of Ag to sapphire by modifying the properties of Ag. Specifically, doping oxide into an Ag layer is investigated. As a result, excellent improvements in adhesion, and particularly in thermal shock resistance, are achieved. A similar effect is observed with various oxides. Additionally, oxide-doped Ag films have a high reflectivity that is almost equal to pure Ag. It is proposed that the adhesion improvement is caused by the formation a pseudotransition layer at the interface between the sapphire substrate and the Ag layer; oxide and Ag coexist in the pseudotransition layer.