1. [1] I.K. Robinson, Phys. Rev., B 33, 3830-3836 (1986).
2. [2] J. Harada, N. Kashiwagura, M. Sakata, and H. Miyake, J Appl. Phys., 62, 4159-4162 (1987).
3. [3] T. Shimura and J. Harada, J Appl. Cryst., 26, 151-158 (1993).
4. [4] Y. Takeda, Y. Sakuraba, K. Fujibayashi, M. Tabuchi, T. Kumamoto, I. Takahashi, J. Harada, and H. Kamei, Appl. Phys. Lett., 66, 332-334 (1995).
5. [5] M. Tabuchi, K. Fujibayashi, N. Yamada, K. Hagiwara, A. Kobashi, T. lguchi, Y. Takeda, and H. Kamei, J Cryst. Growth, 186, 48-54 (1998).