Basic Research on Semiconductor Lasers with Vertical Microcavity

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Various technological approaches have been performed to fabricate quantum dot structures which are potentially useful for optoelectronic device application and basic physics [1]. One of main goals is to manipulate both electrons and photons in nanostructures and microcavities. Towards this goal, it is important to develop nanofabrication and nano-scale optical characterization techniques. In this project, we investigate strained quantum wires and quantum dots for the semiconductor lasers of the next generation.First, we demonstrated spontaneous alignment of InGaAs quantum dots using multi-atomic step structures formed in MOCVD growth [6]. In this technique, first, GaAs epilayr with multi-atomic steps along straight lines was grown on vicinal GaAs substrate under appropriate growth conditions. Then the InGaAs quantum dots were grown selectively on the multi-atomic step edges using strain effects. This growth technique results in spontaneously aligned InGaAs quantum dots without any pre-processing technique prior to the growth.Second, we recently succeeded in fabricating quantum wire laser with vertical microcavity. The quantum wire laser inside the microcavity was fabricated using the selective growth technique. In the microcavity, triangular-shaped In0.3Ga0.7As strained quantum wires are grown between (111)A facets of [011]-oriented GaAs triangular prisms selectively grown on a SiO2 masked DBR mirror region. The quantum wires are comparatively strained owing to the difference of the lattice constants of GaAs and In0.3Ga0.7As. The cavity effect is confirmed by measuring photoluminescence with and without the microcavity. A much sharper photoluminescence spectral line was observed from the quantum wires with the microcavity compared to the sample without the cavity. The lasing oscillation of this sample was demonstrated at 77K,using optical pumping method.