Long wavelength strained layer lasers

Reviews the benefits and consider the influence of strain on the relaxation oscillation frequency, the linewidth enhancement factor and the quenching of the relaxation oscillations. The authors find the relaxation oscillation frequency and their quenching are enhanced in a strained layer laser, while little change is expected in the linewidth enhancement factor by comparison with a lattice-matched quantum well laser. It has been demonstrated that the combination of strain and quantum size effect can lead to the highest hole band being light hole like over a significant energy range in a strained layer structure. The reduced hole effective mass allows the Bernard-Duraffourg condition for population inversion to be satisfied at a lower carrier density. Moreover the differential gain is enhanced due to the ease of penetration of the valence quasi-Fermi level into the band edge. The low effective mass also leads to the virtual elimination of the two major loss mechanisms, Auger recombination and inter valence band absorption, as they are both associated with holes at large wavevector k, and the holes are now confined in a much smaller region of k-space. Consequently, the threshold current density and its temperature dependence are significantly reduced, and the quantum efficiency is improved. The strained layer lasers should be ideal candidates as 1.55 mu m sources for long distance optical communications.<
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