The excitation power dependence of the ground and excited state transitions in type-II InAs-GaAs0.78Sb0.22 quantum dot structure has been studied. Both transitions exhibit a strong blueshift with increasing excitation power but their separation remains constant. This behavior indicates a carrier-induced electric field oriented predominantly along the growth axis, which requires the holes to be localized in the GaAsSb above quantum dots. An accelerated blueshift of the ground state emission is observed once the excited state in the dots starts to populate. This behavior can be explained by a smaller spontaneous recombination coefficient for the excited state transition.

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In order to identify the performance limitations of InGaAs/ AlAs(Sb) quantum cascade lasers, experimental investigations of the temperature and pressure dependencies of the threshold current (I th ) were undertaken. Using the theoretical optical phonon current (I ph ) and carrier leakage (I leak ) to fit the measured threshold current at various pressures, we show that the electron scattering from the top lasing level to the upper L-minima gives rise to the increase in I th with pressure and temperature. It was found that this carrier leakage path accounts for approximately 3% of I th at RT and is negligible at 100 K.