Carrier capture and quantum confinement in AlGaAs/GaAs quantum wire laser structures

We have recently demonstrated room temperature operation of quantum wire (QWR) lasers with threshold currents as low as 0.6 Ma.1,2 A potential problem in using QWRs in laser structures is the very small cross-section of the wire, which can reduce the capture efficiency of injected carriers. We investigated carrier-capture mechanisms in multi-QWR lasers using photoluminescence (PL) and cathodoluminescence (CL) spectroscopy. In our lasers, the crescent-shaped QWRs are formed in situ by OMCVD on V-grooved substrates and are laterally bounded by thinner quantum well (QWL) layers formed on the slopes of the groove. At low temperatures (T < 100 K) we observe two luminescence lines, emitted from the QWR and QWL regions, respectively, as identified by CL imaging. At higher temperatures, the QWR feature becomes dominant, indicating efficient carrier capture from the QWLs to the lower energy QWR potential well. This is confirmed by PL excitation spectra. Two-dimensional quantum confinement in the wires is evidenced by the appearance of the second QWR subband at T > 140 K, with an energy separation of 19 meV, consistent with a model of the QWR subbands. The efficient carrier capture from the QWL region to the QWRs observed in these lasers is important for their efficient operation.