H-POLYTYPE FORMATION IN Zn_1-xMg_xSe. W. Paszkowicz¹, Z. Spolnik¹, F. Firszt² and H. Mêczyñska², ¹Institute of Physics, P.A.S., al. Lotników 32/46, Warsaw, Poland, ²Inst.of Physics, N.Copernicus University, Grudzidzka 5, Toruñ, Poland

Zn_1-xMg_xSe thin layers have been reported to adopt the sphalerite structure type of the substrate for 0<x~<=0.5 [1]. X-ray studies of bulk Zn_1-xMg_xSe crystals grown in the range 0<x<0.56 by the Bridgman method [2,3] have shown that above x~0.2 the structure is of the wurtzite type rather than of the sphalerite type. Powder X-ray analysis of a new crystal prepared from a mixture of pure ZnSe, Mg and Se reveals the presence of the 4H polytype. In the Mg-rich end of the crystal (wurtzite type, x=0.25 determined by EPMA) the 4H phase is not detected while at the other end the amount of 4H is considerable. Due to the lack of pure 4H phase, the structural infor-mation was obtained by Rietveld refinement of the mixture of wurtzite and 4H. For x=0.21, the lattice constants of 4H are a=4.041, c=13.214. The 4H polytype is known in other II-VI systems, e.g. in (Cd,Zn)S and Zn(Se,S) crystals grown by the same method [4]. The polytypism in both (Zn,Mg)Se and Zn(Se,S) ternaries implies the need for studies of the possible polytypes formation in quaterary (Zn,Mg)(Se,S), a component of heterostructures considered for use in blue light emitting diodes and lasers, in order to explain the degradation processes in such electroluminecent devices.

¹H. Okuyama, K. Nakano, T. Miyajima, K. Akimoto, Jpn. J. Appl. Phys. 30 (1991) L1620; D. Huang, C. Jin, D. Wang, X. Liu, J. Wang, X. Wang, Appl. Phys. Lett. 67 (1995) 3611-3613

²F. Firszt, H. Mêczyñska, B. Sekulska, J. Szatkowski, W. Paszkowicz, J. Kachniarz, Semicond. Sci. Technol. 10 (1995) 197

³F. Firszt, S. Lêgowski, H. Mêczyñska, H.L. Oczkowski, W.O siñska, J. Szatkowski, W. Paszkowicz, Z.M. Spolnik, J.Cryst.Growth (1995), in print

⁴M.J. Kozielski, J.Cryst.Growth 30 (1975) 86