Strain and quantum-confinement effects on differential gain of strained InGaAsP/InP quantum well lasers

The effects of both strain and quantum confinement on the differential gain of strained InGaAsP/InP quantum well lasers (QWLs) are studied on the basis of valence-band structures calculated by k⋅p theory. Using an InGaAsP quaternary compound as an active layer makes it possible to separate the effect of strain (both tensile and compressive) from the quantum-confinement effect. In tensile-strained quantum wells, both strain and quantum-confinement effects exert a significant influence not only on the valence-band density of states (DOS) but also on the valence-subband energy spacings. In compressive-strained wells, on the other hand, the strain and quantum-confinement effects play an independent role in determining the DOS and the subband energy spacings, respectively. On the basis of these characteristic features of the valence-band structure of strained quantum wells, we discuss basic design principles for strained QWLs with larger differential gain.