1. D.E. Holms, R.G. Wilson and P.W. Yu,J. Appl. Phys. 52,3396 (1981).
2. C. Blaauw, B. Emmerstorfer, R.A. Bruce and M. Benzaquen,Proc. 6th Conf. on Semi-insulating III-V Materials, Toronto, 1990 (IOP, 1990), p. 137.
3. C. Miner, D.G. Knight, J.M. Zorzi, R.W. Streater, N. Puetz and M. Ikisawa, Inst. Phys. Conf. Ser. No. 135Proc. DRIP VI, Santander, 1993, (1994), p. 181.
4. D. Hofmann, G. Müller and N. Streckfuß,Appl. Phys. A 48, 315 (1989).
5. K. Kainosho, H. Shimakura, H. Yamamoto and O. Oda,Appl. Phys. Lett. 59, 932 (1991).