1. P. Rappaport, RCA Rev. 20, 373 (Sep 1959)
2. S. Matlow, US Patent #2, 984, 775 (5-1961)
3. P.A. Iles, Conf. Rec. on IEEE Photovolt. Spec.Conf. p.1 (May 1972)
4. E.L. Ralph, Proc. 11th IEEE Photovolt Spec.Conf., p.31 5, (1975)
5. B. Ross and D.B. Bickler, Proc. 3rd E.C. Photovolt, Solar Energy Conf. p.674 Cannes, France (Oct. 1980)