TEMPERATURE-DEPENDENCE OF STRAINS AND STRESSES IN UNDERCRITICAL CUBICSUPERLATTICES AND HETEROJUNCTIONS

Strained superlattices and heterojunctions subject to variable tempera ture exhibit changes in their elastic and/or thermal strain and stress components, relative to their values at room temperature. We consider systems grown in arbitrary directions, with thicknesses smaller than the critical value (undercritical systems). In lowest order, the chang es are linear with the temperature. The dependence on temperature of t he thermal expansion coefficients is taken into account and shown to i mprove agreement with data. Criteria are established for predicting th e form of such changes in any combination of material constituents. Sp ecific applications are treated in detail and comparison is made with existing data from the literature. The effective linear thermal expans ion coefficients of the structure, parallel and perpendicular to the d irection of growth, are formulated explicitly. The present results are transcribed to the parallel problem of a hydrostatic pressure in the most general case; this extends previously published work, which refer s to material constituents with a lattice misfit smaller than the bulk modulus misfit. The latter assumption ib valid for most material comb inations but not all.