PURE STRAIN EFFECT ON DIFFERENTIAL GAIN OF STRAINED INGAASP/INP QUANTUM-WELL LASERS

Pure strain effect on differential gain of strained InGaAsP/InP quantum-well lasers (QWL's) is analyzed on the basis of the valence band structures calculated by k . p theory. By using an InGaAsP quaternary compound as an active layer, it becomes possible to study the relationship between the differential gain and the amount of strain (both tensile and compressive) when both the quantum-well thickness and the emission wavelength are kept constant. It is clarified that the tensile strain not only reduces the density of states in the valence band but also increases the energy spacings between the first two valence subbands. Due to these characteristic features of tensile strain, it is concluded that tensile strain has a more pronounced impact on the improvement of differential gain in InP-based, strained QWL's as compared with compressive strain.