Mysterious Material InN in Nitride Semiconductors - What's the Bandgap Energy and its Application?

The progress in nitride semiconductors is reviewed. The current status in the growth and characteristics of InN, which remains the most mysterious compound, is reviewed. The phase diagram for InN growth, the optical absorption characteristic, polarity, temperature dependence of photoluminescence, future prospects are described. The application of InN for light emitting devices is discussed.