Improvement of crystal quality and laser characteristics by zero net strain structure

Zero net strain structure is very useful for strained multiple quantum well (MQW) lasers for which many numbers of quantum wells are required. We demonstrate the effectiveness of the zero net strain structure to prevent the degradation of the crystal quality up to 15 wells, which cannot be realized by the conventionally strained MQW (well: 1.5% compressive strain, 30 Angstrom thick). We also show that the zero net strain structure has finite critical thickness and dislocations other than 60 degrees misfit dislocations are introduced into the zero net strain structure beyond the critical thickness. Narrower distribution of threshold current than that of the conventionally strained lasers, high relaxation oscillation frequency of 5.5 GHz/root mW and high differential gain of 6.3 x 10(-16) cm(2) have been realized for the cm 1.55 mu m laser with zero net strain MQW with 15 wells by the suppression of degradation of crystal quality.