Expected pronounced strengthening of II-VI lattices with beryllium chalcogenides

To our knowledge, the suggestion, based on material calculation, of the utilization of beryllium chalcogenides-based materials, BeX(X = S, Se, Te) as novel II-VI epitaxial layers, was proposed recently in published communications (C. Verie, Condensed Matter Meet. JMC-4. Rennes: France, Aug. 31-Sept. 2, 1994, published in Abstract Booklet, French Physical Society, Paris, 1994; C Verie, in B. Gil and R.L. Aulombard (eds.), Semiconductor Heteroepitaxy, Growth, Characterization and Device Applications, World Scientific. Singapore, 1995, pp. 73-78.). In the present work, this is discussed in the context of the unsolved question of appropriate long lifetime CW operation in (Zn, Cd)(S, Se)-based blue laser at T greater than or equal to 300 K. The shear modulus C-s = (C-11 - C-12)/2 is identified to be a key structural signature of the material. Making use of the Harrison bond-orbital model, the calculation of C-s leads to a simple semi-empirical expression. Its plot versus the Harrison covalency scale-based Variable demonstrates good agreement with all experimental data for the tetra-coordinated semiconductors. Prediction capabilities are exploited: (i) the alloys (Zn, Cd)(S, Se) belong to a cluster of materials having an ionicity-induced softening of the lattice; (ii) the problem of high-quality epitaxy using a compound with ionicity values above the critical one, e.g., MgX (X = S, Se); (iii) the BeX samples exhibit C-s of the order of or even higher than, that of Si or GaAs. This work suggests novel possibilities for hardening the lattice in II-VI alloys, leading to a 'covalency engineering' of blue laser epilayers. (C) 1997 Elsevier Science S.A.