At the weakest excitation power of 1.6 mW, there are two peaks in the PL spectrum.
Each spectral peak represents the emission from QWRs and Side-QWs respectively.
The QWR PL energy was lower by 50 meV from the lasing photon energy, while the PL energy of Side-QW was higher by 35 meV from the lasing energy.
We expect that there exists several subband states of QWR between ground state QWR states and side-QW states.
So we believed that the origin of stimulated emission is the higher order subbands transitions of carriers in QWRs.
To investigate more clearly about the origin of stimulated emission, we used PL imaging measurement.
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