1.5 μm wavelength InGaAs/InGaAsP distributed feedback multi-quantum-well lasers grown by chemical beam epitaxy

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Abstract
We demonstrated the first successful growth of 1.5 μm strained-layer InGaAs/InGaAsP multi-quantum-well (MQW) distributed feedback (DFB) lasers by chemical beam epitaxy (CBE). In these DFB wafers, a quaternary grating is placed at the bottom of the MQW stack with an InP spacer layer. Studies by transmission electron microscopy show that defect-free InP regrowth was achieved with no mass transport needed over the grating corrugations before regrowth. With CBE regrowth the shapes of the gratings were well preserved. The InP overlayer also very effectively smoothed out the quaternary surface corrugations resulting in very flat MQW structures. Buried-heterostructure 6-QW DFB lasers (250 μm long and as-cleaved) operated at 1.55 μm with cw threshold currents 10–15 mA and slope efficiencies up to 0.35 mW/mA (both facets). Side-mode suppression ratios (SMSR) as high as 49 dB was obtained. The laser operated in the same DFB mode with SMSR staying above 40 dB from threshold and throughout the entire current range even at high temperatures (70 °C checked).