1. Properties, Processing and Applications of Gallium Nitride and Related Semiconductors, edited by J.H. Edgar, S. Strite, A. Akasaki, H. Amano, C. Wetzel, Emis Data reviews Series (Inspec, London, 1999), Vol. 23
2. B. Damilano et al., Appl. Phy. Lett. 75, 962 (1999)
3. M.E. Lines, A.M. Glass, Principles and Applications of Ferroelectrics and Related Materials (Clarendon Press, Oxford, 1977)
4. N. Takeuchi, Phys. Rev. B 65, 045204 (2002)
5. N. Farrer, L. Bellaiche, Phys. Rev. B 66, 201203(R) (2002)