Effects of growth orientation on the properties of strained semiconductor quantum well lasers

ABSTRACT \ EFFECTS OF GROWTH ORIENTATION ON THE PROPERTIES OF STRAINED SEMICONDUCTOR QUANTUM WELL LASERS ODUNCUOGLU Murat M. Sc in Physics Engineering Supervisor: Assoc. Prof. Dr Beşire GÖNÜL January 2000, 77 Pages The work described in this thesis investigates how strain and crystal orientation affect the band structure of quantum well lasers. The study provides a better understanding of the dependence of effective mass, strain-induced band-edge shift, change in the band-gaps and emission wavelengths on the substrate orientation. A detailed calculation of the confined states considering the effects of well width, substrate orientation, piezoelectric field, band-offsets, transition strengths of allowed and forbidden transitions was carried out. The lack of inversion symmetry in polar, zinc-blende crystals when grown on axes other than (001) leads to the formation of internal piezoelectric fields when such structures are strained. The built-in electric field modifies the electronic uistructure and optical properties of the crystal. Recently, it has been suggested that piezoelectric quantum well lasers operated under forward bias could be used in an integrated laser. Design of such devices requires a knowledge of the behaviour of the quantum well structure as a function of carrier and current densities. It has been shown previously that maximum gain reduces with increasing piezoelectric field. We explain the reductions of maximum gain in the presence of internal piezoelectric fields considering the overlaps between envelope functions of the confined states. Keywords: Quantum wells, growth orientation, strain, critical thickness, optical gain IV