Using wide bandgap semiconductors, we are developing innovative semiconductor devices as well as investigating material physics in the following areas.

(1)   Optical device physics in ultra-violet (UV) LED and optical devices using micro-facet. (by Dr. Nishida and Dr. Akasaka)

(2)   Electronic device physics such as carrier transport in nitride HBTs and diamod FETs. (by Dr. Kumakura, Mr. Yamauchi, Dr. Makimoto, and Dr. Kasu)

(3)   Impurity doping into wide-bandgap semiconductors and its characterization. (by Dr. Taniyasu and Dr. Kasu)

(4)   Developing new wide-bandgap materials such as InN and diamond. (by Dr. Matsuoka and Dr. Kasu)

　　Among the above field, highlights obtained in 2002 are the development of a GaN/InGaN HBT (See Makimoto) and the material physics relating to InN　(See Matusoka).

GaN/InGaN HBT (2002 Highlight) 
　　We have successfully fabricated an Npn-type GaN/InGaN heterojunction bipolar transistor (HBT) using the base regrowth technique to improve the ohmic characteristics. The HBT characteristics were drastically improved and the current gain increased up to 3000, which is 100 times as high as that of the previous world-record for nitride HBTs. This demonstrates that a nitride HBT is promising for the future high-power electronic devices.

Material Physics of InN (2002 Highlight)

　　We have clarified the bandgap energy of InN, which was believed to be about 1.9 eV for more than a quarter century. Recently, we found that our experimental data do not support the previous value, so we grew a high-quality InN epitaxial layer to investigate its bandgap energy. Then, the real bandgap energy of InN has been proved to be about 0.9 eV, indicating that InN is a promising material for an optical device for the communications.

Highly-efficient UV-LED (Highlight 2001)

　　Possible wavelength by AlGaN active layer covers from 200 to 360 nm, and we demonstrated high output power of 10 mW, i.e., one order of magnitude larger output than previous reports, at 352 nm wavelength. Nitride material containing Al is shown to have strong potential for highly-efficient LEDs in UV region.