Electronic states in InN and lattice dynamics of InN and InGaN
During a private discussion at the International Workshop on Nitride Semiconductors (IWN-2000) in Nagoya in the autumn of 2000, one of the authors (VD) mentioned to Prof. F. Bechstedt from Friedrich-Schiller-University (Jena, Germany) and Prof. H. Harima from Osaka University (Japan) that, according to the experimental results obtained at Ioffe Institute (St. Petersburg, Russia) for InN and In-rich InGaN alloys grown by plasma-assisted MBE at Ioffe Institute and metal-organic MBE at Hannover University (Germany), the true band gap of InN was of the order of 0.9 eV or even less, which was well below the commonly accepted value of 1.89 eV [6.1]. Among the main arguments was the observation of the absorption edge in the region of 0.9 eV, its high-frequency shift with increasing free carrier concentration (which was attributed to the Burstein-Moss effect [6.2]), the observation of intense IR luminescence near the absorption edge, and, lastly, a regular shift of the absorption edge and edge luminescence to higher energies with increasing Ga concentration in In-rich InxGa1−xN alloys (0.4 < x < 1). The response of Friedhelm Bechstedt was surprising. He said that, in early 2000, his group obtained a band gap value of the order of 1 eV in ab initio calculations of the electronic structure
of hexagonal InN. However, they had not published these results because of strong criticism from colleagues.