Control of Spontaneous Emission from Selectively Grown Semiconductor Photonic Dots

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Vertical cavity surface emitting lasers (VCSELs) are expected to play an important role for optical parallel information processing, and the integration of VCSELs has been studied. Since the integration needs very high uniformity of the lasing threshold, it is very difficult to realize large-scale integration. In this respect, it will be ideal if we could realize thresholdless lasers in near future. In this project, three-dimensional photonic confinement structure based on a pyramid was fabricated and exciton-photon interactions were studied to control the spontaneous emission processes, which will lead to realize such a thresholdless laser operations.Three-dimensional optical microcavities were prepared with ZnS pyramids selectively grown on GaAs substrates. The resonance Q values as large as 〜5000 was observed in the wavelength region of 〜400 nm. Since GaAs is lossy material in this wavelength range, it is a surprise to have such a high resonance Q value. This was attributed to the l … More arge enough difference of the refractive indices with the contribution from the X and L indirect band transitions, which have the very large density of states in this wavelength range. By extending this finding to more arbitrary wavelength, three-dimensional optical microcavities made of ZnS pyramids were grown on ZnSe -based distributed Bragg reflectors (DBRs), where DBR is expected to function as an efficient reflector from the base plane of the pyramids. Such ZnS pyramids grown on the DBRs were embedded with CdS quantum dots to study the exciton-photon interactions. The pyramids showed the resonance Q values over 1000 and spontaneous emission from the CdS quantum dots was well enhanced by the coupling to the resonance modes. The enhanced PL peak as well as the half width exhibited highly temperature-stabilized properties. This demonstrated that the enhanced peak is well controlled by the cavity properties, not by the semiconductor light emitter. This demonstrated the nice features of the very low temperature dependence of the spontaneous emission, which is one of the important issue for optical communications with wavelength multiplexing. Less