Threshold currents of 1.3-/spl mu/m bulk, 1.55-/spl mu/m bulk, and 1.55-/spl mu/m MQW DFB P-substrate partially inverted buried heterostructure laser diodes

We investigate the threshold currents of 1.3-/spl mu/m bulk, 1.55-/spl mu/m bulk, and 1.55-/spl mu/m multi-quantum-well (MQW) distributed feedback (DFB) P-substrate partially inverted buried heterostructure (BH) laser diodes experimentally and theoretically. In spite of the larger internal loss of the 1.55-/spl mu/m bulk laser diodes, the threshold current of the 1.55-/spl mu/m bulk DFB P-substrate partially inverted BH laser diode is almost the same as that of the 1.3-/spl mu/m bulk DFB P-substrate partially inverted BH laser diode. The experimentally obtained average threshold current of the 1.3-/spl mu/m bulk DFB P-substrate partially inverted BH laser diodes is 17 mA and that of the 1.55 /spl mu/m bulk DFB P-substrate partially inverted BH laser diodes is 16 mA. The calculated threshold current of the 1.3-/spl mu/m bulk DFB laser diode is 15.3 mA and that of the 1.55-/spl mu/m bulk DFB laser diode is 18.3 mA, which nearly agree with the calculated values, respectively. We have fabricated two types of five-well 1.55-/spl mu/m InGaAs-InGaAsP MQW DFB P-substrate partially inverted BH laser diodes. One has barriers whose bandgap energy corresponds to 1.3 /spl mu/m, and the other has barriers of which bandgap energy corresponds to 1.15 /spl mu/m. The calculated threshold current of the MQW DFB laser diode with the barriers (/spl lambda//sub g/=1.3 /spl mu/m) is 8.5 mA, which nearly agrees with the experimentally obtained value of 10 mA. However, the calculated threshold current of the MQW DFB laser diode with the barriers (/spl lambda//sub g/=1.15 /spl mu/m) is 7.9 mA which greatly disagrees with the experimentally obtained value of 19 mA, which suggests that the valence band discontinuity between the well and the barrier severely prevents the uniform distribution of the injected holes among five wells.