Effect of surface defects on InGaAs/InAlAs Quantum Cascade mesa current-voltage characteristics

We investigate the impact of surface defect density on the transport properties of molecular beam epitaxy grown InGaAs/AlInAs Quantum Cascade (QC) structures. We examine six parameters of the current-voltage (IV) characteristics of the QC mesas: turn-on voltage, turn-on current density, turn-on differential resistance, differential resistance, cut-off voltage, and cut-off current density. The analyses for pulsed mode operation (T=80 K and 300 K) and continuous wave (CW) operation (80 K) show that all six parameters are only weakly correlated to surface defects. The turn-on voltage and current density share a negative correlation with defects (>-0.26) in both pulsed mode and CW operation at 80 K, and a positive correlation in pulsed mode at 300 K (<0.21). The cut-off voltage has a positive correlation in all three modes of operation (<0.51). The cut-off current density has a positive correlation (<0.39) in both pulsed mode (80 K and 300 K) and a negligible correlation in CW operation (80 K). We observed insignificant correlation coefficients (<0.1) for differential resistances at 80 K along with a weak negative correlation (>-0.29) in pulsed mode at 300 K. Our analysis demonstrates that shallow oval and a few deep oval defects have little influence on IV.