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. Vèrié, Condensed Matter Meet. JMC-4, Rennes, France, Aug. 31–Sept. 2, 1994, published in Abstract Booklet, French Physical Society, Paris, 1994; C. Vèrié, 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 ⩾ 300 K. The shear modulus Cs = (C11–C12)/2 is identified to be a key structural signature of the material. Making use of the Harrison bond-orbital model, the calculation of Cs 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 Cs 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.