1. Davies, S.R., Cunningham, C.T., Little, L.T. and Matheson, D.N.: Int. J. of Infrared and Millimeter Waves (this issue) (1992).
2. Honingh, C.E., Dierichs, M.M.T.M., Schaeffer, H.H.A., Klapwijk, T.M., de Graauw, Th., 2nd Int. Symposium. on Space Terahertz Technology, 473 (1991).
3. Padman, R.: Int. J. of Infrared and Millimeter Waves10, 1233 (1989).
4. Pan, S.K., Kerr, A.R., Feldman, M.J., Kleinsasser, A.W., Stasiak, J.W., Sandstrom, R.L. and Gallagher, W.J.: IEEE Trans. Microwave Theory Tech.MTT-37, 580 (1989).
5. Sutton, E.C., Danchi, W.C., Jaminet, P.A. and Ono, R.H.: Int. J. of Infrared and Millimetre Waves,11, 133, (1990).