Photonic Crystal Cavities For Spectrally-selective Optoelectronic Devices
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Photonic crystal (PC) structures exhibit unconventional dispersion and refractive properties making possible hitherto not realizable optical and optoelectronic devices with high spectral selectivity. Functional PC devices (e.g., optical filters, reflectors, and photo detectors and light emitters) on both Si and III-V semiconductor material systems were fabricated via E-Beam lithography (EBL). The device layer can be further transferred onto foreign substrates such as glass or plastic (PET), using a low-cost "wet nanomembrane transfer technique" developed in this study.The broadband membrane reflectors (MR) based on Fano resonances in patterned silicon nanomembranes have been demonstrated. Resonance control of the reflectors was realized either by partially removing buried oxide layer underneath the device layer, or by controlled SiO2 film deposition on the top of the devices. Both blue- and red-shifts were demonstrated with a turning range of 50 nm for a center wavelength at 1550 nm. These results demonstrate practical post-process means for Fano resonance engineering for both narrow band filters and ultra-compact broadband reflectors.An optically pumped resonance cavity light emitting device (RCLED) with Si based membrane reflectors (MR) has been demonstrated experimentally. The stimulated cavity mode at 1545 nm was observed at room temperature with a pulsed green pumping laser light source. We observed significant spectral narrowing in RCLEDs with linewidth reduced from 50 nm down to <4 nm, owing to the presence of top and bottom MR reflectors. The measured photoluminescence efficiency also increased by a factor of 100 in RCLEDs, as compared to the value measured from as-grown InGaAsP QW structures on InP substrate. The mode shifts were also investigated over different temperatures and different pumping power levels. An InGaAsP QW LED array device was also fabricated and transferred onto flexible PET substrate. The devices showed very good electrical and optical performances, based measured L-I-V (light-current-voltage) characteristics and spectral and near field images. All these work can lead to the demonstration of an electrically pumped membrane-reflector vertical-cavity surface-emitting laser (MR-VCSEL).