1. R.T. Davies, J.T. Glass: Adv. Solid State Chem.2, 1 (1991)
2. G. Pensl, R. Helbig: Adv. Solid State Phys.30, 133 (1990)
3. J.A. Powell, P.G. Neudeck, L.G. Matus, J.B. Petit: Mater. Res. Soc. Symp. Proc.242, 495 (1990)
4. CREE Research Inc., Durham, NC 27713, USA
5. G. Krötz, W. Hellmich, G. Müller, G. Derst, S. Kalbitzer: Nucl. Instrum. Methods B80/81, 927 (1993)