Nanosize Stress Concentrators at Facets in Zn1-xCdxSe/ZnSe Multiple Quantum Well Laser Structures

Strained layer Zn1-xCdxSe/ZnSe multiple quantum well structures are presently at the core of most blue-green lasers. Laser degradation has focused attention on such issues as residual strain, stress concentration, and dislocation nucleation and propagation in these materials. We fabricated Fabry-Perot cavities through cleavage in Zn1-xCdxSe/ZnSe multiple quantum well structures grown by molecular beam epitaxy with x = 0.24, 0.3 and x = 0.50 and a variety of quantum well parameters. The cavity facets were examined by means of atomic force microscopy and lateral force microscopy. We found previously unreported, cleavage-induced nanosize defects related to the discontinuity in the mechanical properties of the strained layer quantum wells. In most cases, the defects can be assimilated to surface delamination features preferentially located at the boundaries between the strained active ternary material and the relatively unstrained binary buffer or barrier layers. Such features run parallel to the interface, exhibit typical depths and surface widths in the 10 nm range, and may act as important stress concentrators during laser processing and operation.