Radiative performance of strained-layer lasers

Abstract

It is shown that application of biaxial tension to the active region of a bulk-like III–V semiconductor laser can significantly enhance TM gain compared to TE gain and reduce the threshold current density, owing to improved suppression of spontaneous emission polarised in the growth plane of the laser structure. The differential gain is enhanced compared to unstrained structures, and a larger peak gain can be achieved than in comparable structures under biaxial compression. The authors include the spin-split-off band in their calculations and show that the strain-induced interaction with this band has a significant influence on the character of the valence states, particularly in tensile-strained structures. Using idealised quantum-well calculations, the authors investigate the effect of changing the valence band mass mv with respect to the conduction band mass and how this affects the radiative properties of a laser structure. It is shown that, although it is indeed the case that the transparency carrier density always increases with increasing mu, for the authors' ideal model, the radiative current density can decrease.