EFFECT OF FREE-CARRIERS ON THE LINEWIDTH ENHANCEMENT FACTOR OF INGAAS/INP (STRAINED-LAYER) MULTIPLE QUANTUM-WELL LASERS

In this letter the linewidth enhancement factor measured from a tensile strained, a compressively strained, and a lattice matched InGaAs/InP multiple quantum well laser is analyzed taking free-carrier effects into account. We find that the free carriers in the wells of compressively strained and lattice matched structures degrade the linewidth enhancement factor by about 40% due to the plasma effect. In tensile strained TM polarized lasers however, carrier movement parallel to the E vector is inhibited due to the quantum confinement, allowing a linewidth enhancement factor as low as 1.6 at the peak wavelength. Heterobarrier carrier leakage must be prevented using sufficiently large band-gap barrier and separate confinement layers, otherwise the free carriers in these layers result in an additional degradation of the linewidth enhancement factor.