Epitaxial growth of semiconductors under pseudomorphic conditions leads to stabilization of crystallographic structures that are unstable at equilibrium is observed. For example, the stable phase of MnTe is NiAs, but epitaxial layers of MnTe with the zinc blende structure have been grown on GaAs substrates [1]. Stability of a given phase of the overlayer depends on parameters such as its lattice constant, and also - in the case of alloys - on the alloy composition.

Using Density Functional Theory within the Local Spin Density Approximation and atomic pseudopotentials we have studied phase stability, elastic properties, and electronic structure of ZnO, ZnTe, and MnTe. We have considered NiAs, wurtzite (W), and zinc blende (ZB) structures. As a result we have obtained the equilibrium lattice parameters for all considered phases and their elastic constants, together with pressure coefficients of the band gaps. In agreement with experiment we find that the stable phase of ZnO is W, lower in energy by 10 meV/atom than the ZB phase, while cubic ZnTe is more stable by 5 meV/atom than the W phase. For both crystals, the NiAs structure is highly unfavorable, being higher in energy by 250 meV/atom. On the other hand, the stable structure of the antiferromagnetic semiconductor MnTe is NiAs, which are lower in energy than the ZB and the W phases by about 100 meV/atom. Finally, we have considered Mn_xZn_1-xTe alloy, which according to our calculations changes the equilibrium phase from NiAs to ZB for the Mn content of about 0.75. The impact of the magnetic ordering on the stabilization of crystalline phases will be discussed. The calculated bowing parameters of the energy gap of Mn_0.5Zn_0.5Te in NiAs and ZB phases are small, and equal to 0.05 and 0.09 eV, respectively. A comparison with experimental morphology [1] of Mn_xZn_1-xTe will be given.


[1] E. Przeździecka et al., to be published.

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