Tunneling injection (TI) quantum dot (QD) amplifier has been investigated in multi-wavelength pump probe system allowing to time and spectrally resolve gain dynamics with a sub-picosecond resolution across all inhomogeneously broadened ensemble of QDs. The gain medium we studied comprised six QD layers, each accompanied by a TI quantum well separated by a 2 nm barrier.

We have demonstrated two tunneling processes, resonant (RT) and non-resonant (NRT), occurring simultaneously at different spectral location of QDs. RT has been observed broaden to about 10meV, which confirms the theoretical prediction. NRT has been measured nearly bias insensitive in a narrow region of high energy QDs.

We have discussed the importance of the energetical alignment of the tunneling injection well and QDs at gain peak (from where a lasing occurs). Otherwise, the tunneling injection processes feed the QDs that do not contribute to laser emission. Thus, becoming a loss mechanism, the tunneling injection can deteriorate the lasers performance.

Observing the RT to be clearly the most efficient tunneling injection mechanism, we suggest the design of tunneling QD based lasers to ensure the RT to contribute for a stimulated emission.