Exciton Electroluminescence of ZnSe/ZnO Structures under Biaxial Stress

Abstract

Due to the lattice mismatch between the epilayer and the substrate in ZnSe/ZnO stuctures, it is cucial to know the limiting conditions leading to a pseudomorphic growth by the accommodation of the biaxial strains caused by difference in lattice constants and/or thermal expansion coefficients of the materials forming the heterostucture [1, 2]. Moreover, hydrostatic pressure decreases the lattice constant of the materials. The difference in the compressibility of ZnO from that of ZnSe generates under hydrostatic pressure a tensile strain which progressively compensates the lattice mismatch induced compressive strain. The valence band at the Γ point of the unstrained ZnSe crystals consists of a fourfold degenerate P3/ 2 valence band (J = 3/2, m = ±3/2, m = ±1/2). Under biaxial compressive or tensile stress this valence band splits into a light-hole (J = 3/2, mj = f 1/2) and a heavy-hole (j = 3/2, m = ±3/2) branches [3-5]. The trend in II-VI compounds is that the materials have a larger negative deformation potential as their lattice constants get smaller. It may be suspected that the deformation potential will get more negative as we apply pressure, since the average lattice constant gets smaller [3]. In addition, a situation similar to the pressure induced biaxial strain can occur for heterostructures where the thermal expansion coefficients for materials vary greatly. The lattice constants of constituent materials at each temperature must adjust each other. In this paper, we present for the first time a study of the exciton emission of the strained ZnSe/ZnO stuctures as a function of the biaxial compressive or tensile stress and temperature using photo and electroluminescence methods. These