THRESHOLD CURRENTS OF 1.3-MU-M BULK, 1.55-MU-M BULK, AND 1.55-MU-M MQW DFB P-SUBSTRATE PARTIALLY INVERTED BURIED HETEROSTRUCTURE LASER-DIODES

We investigate the threshold currents of 1.3-mu m bulk, 1.55-mu m bulk , and 1.55-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-mu m bulk laser diodes, the threshold current of the 1.55 -mu m bulk DFB P-substrate partially inverted BH laser diode is almost the same as that of the 1.3-mu m bulk DFB P-substrate partially inver ted BH laser diode, The experimentally obtained average threshold curr ent of the 1.3-mu m bulk DFB P-substrate partially inverted BH laser d iodes is 17 mA and that of the 1.55 mu m bulk DFB P-substrate partiall y inverted BH laser diodes is 16 mA, The calculated threshold current of the 1.3-mu m bulk DFB laser diode is 15.3 mA and that of the 1.55-m u m bulk DFB laser diode is 18.3 mA, which nearly agree with the calcu lated values, respectively, We have fabricated two types of five-well 1.55-mu m InGaAs-InGaAsP MQW DFB P-substrate partially inverted BH las er diodes, One has barriers whose bandgap energy corresponds to 1.3 mu m, and the other has barriers of which bandgap energy corresponds to 1.15 mu m. The calculated threshold current of the MQW DFB laser diode with the barriers (lambda g = 1.3 mu m) is 8.5 mA, which nearly agree s with the experimentally obtained value of 10 mA, However, the calcul ated threshold current of the MQW DFB laser diode with the barriers (l ambda g = 1.15 mu m) is 7.9 mA which greatly disagrees with the experi mentally 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.