Threshold currents of 1.55 μm InGaAs/InGaAsP multiple quantum well laser diodes

Abstract

We investigate threshold currents (Ith’s) of 1.55 μm InGaAs/InGaAsP multiple quantum well (MQW) distributed feedback (DFB) laser diodes (LDs) experimentally and theoretically. The measured Ith of the 1.55 μm MQW LD with barriers whose band gap energy corresponds to 1.3 μm (λg=1.3 μm) is 10 mA, which nearly agrees with the calculated value of 8.5 mA. However, the measured Ith of the 1.55 μm MQW LD with barriers (λg=1.15 μm) is 19 mA, which is much larger than the calculated value. We explain this discrepancy by a nonuniform distribution of injected holes among the wells. The separation, ΔEv1, between the first quantized level of hole for the well valence band and the top energy for the barrier valence band prevents a uniform distribution of holes among the wells. The re-evaluated Ith, taking into account ΔEv1, is 18.8 mA which agrees well with the measured one. We also show that 1.55 μm p-type doped MQW DFB LD with barrier (λg=1.15 μm) is 5.4 mA, which is comparable to Ith’s of 1.55 μm strained MQW DFB LDs.