Tamura exhibited white LED using oxidation*

Tamura Manufacturing Co., Ltd. and its subsidiary, Lightwave Corporation, have developed a white LED using bismuth oxide (β-Ga2O3) and exhibited it at the "3rd LED and Organic EL Lighting Fair in Japan" (16-18 January 2013 in Tokyo. International Exhibition Center held) on display. The LED uses a phosphor in combination with a GaN-based semiconductor blue LED chip fabricated on a β-a2O3 substrate. The selling point is that it has a feature that it is easy to increase the light output power compared with the case of using a general blue LED chip fabricated on a sapphire substrate.

Tamura Manufacturing Co., Ltd. and Lightwaves displayed two white LEDs using 0.3mm square and 2mm square blue LED chips, respectively. The 0.3mm square product is a 400mA drive type, and the 2mm square product is a 6A drive type. The brightness of the 2mm square product is about 500lm, "the goal is to improve the 2000-3000lm that is difficult for a sapphire substrate type product" (narrator).

Since the sapphire substrate has insulation properties, the sapphire substrate type product must adopt a lateral structure in which the anode electrode and the cathode electrode are arranged transversely. On the other hand, the β-Ga2O3 substrate has a high conductivity, so that a vertical structure in which the anode and the cathode are formed on the front and back surfaces of the LED chip can be used. Compared with the lateral structure, the vertical structure not only reduces the element resistance and the thermal resistance, but also makes the current distribution more uniform. The smaller the element resistance and the thermal resistance, the less heat is generated by the LED chip, so it is suitable for a large current drive.

Although GaN substrates are also suitable for making high-power LEDs, "the cost of adopting β-Ga2O3 substrates is lower" (narrator). At present, a GaN substrate is manufactured using a vapor phase growth method called HVPE, and a β-Ga2O3 substrate is a solution growth method. In theory, the solution growth method is more suitable for improving the quality and size of the substrate.

At present, the diameter of the manufactured β-Ga2O3 substrate is 2 inches. Tamura Manufacturing Co., Ltd. plans to trial production of 4-inch products in 2014 and officially launch products in 2015. In addition, it will also challenge the development of products with a 6-inch diameter.