8-band k.p theory of the material gain of strained tetrahedral semiconductors: application to 1.3 μm-InGaAsP lasers subject to additional external uniaxial stress

Numerical and experimental results are presented for bulk 1.3 μm-InGaAsP on InP subject to internal biaxial strain in the xy-plane (active layer, strain axis in growth or z direction) and/or external stress along the lateral, x direction. This uniaxial stress by an external force acting perpendicular to the built-in biaxial strain provides an additional degree of freedom for studying the strain dependence of electron states and, thus, of device properties. The material gain is calculated using a novel method for efficient Brillouin-zone integration. The maximum linear gain is parametrised as g(n)=a(n-n_l) for TE- and for TM-polarised light, and the strain dependence of differential gain a and of transparency density n is calculated and discussed in terms of symmetry. The theoretical results compare well with measurements of threshold currents and emission-wavelength differences at TE-TM switching of ridge-waveguide laser diodes