Reproducible growth of narrow linewidth multiple quantum well graded index separate confinement distributed feedback (MQW-GRIN-SCH-DFB) lasers by MOVPE

We describe reproducible growth of multiple quantum well graded index separate confinement distributed feedback (MQW-GRIN-SCH-DFB) lasers by atmospheric pressure metalorganic vapor phase epitaxy (MOVPE). Epitaxial layers were grown directly on a first order grating prepared on a (100) n-InP substrate. The gratings were preserved by introducing a suitable mixture of AsH3 and PH3 into the reactor. The quality of epitaxial layers grown on preserved gratings was found to improve by deposition of a very thin quaternary layer (7 nm thick) at low temperature (500-degrees-C), before the growth of the waveguide and subsequent graded index layers at the normal growth temperature (625-degrees-C). With the cavity length varied from 0.5 to 2 mm, the corresponding threshold currents were 22 and 100 mA, respectively. A remarkable improvement in both laser linewidth and output power was observed with devices as long as 2-3 mm. With 2 mm long device we observed linewidth as narrow as 600 kHz at a power output of 35 mW.