Blue InGaN/GaN-based Quantum Electroabsorption Modulators

We introduce InGaN/GaN-based quantum electroabsorption modulator that incorporates ~5 nm thick In_0.35Ga_0.65N/GaN quantum structures for operation in the blue spectral range of 420-430 nm. This device exhibits an optical absorption coefficient change of ~6000 cm^-1 below the band edge at highly transmissive, blue region (at lambda_peak=424 nm) with a 6 V swing and emits blue light (at lambda_peak=440 nm) with an optical output power of 0.35 mW at a 20 mA current injection level. Unlike infrared III-V quantum modulators, this blue modulator shows a blue shift in its electroabsorption (for lambda < 418 nm) with increasing applied field accross it, due to high alternating polarization fields in its quantum structures; this electroabsorption behavior is opposite to the conventional quantum confined Stark effect that features common red shift. This device holds great promise for > 10 GHz optical clock injection directly into silicon CMOS chips in the blue because of its low parasitic in-series resistance (< 100 Omega) and the possibility to make smaller device mesas for low capacitance (1.2 fF for a 10 mum x 10 mum mesa size). Considering high-speed operation and high responsivity of silicon-on-insulator (SOI) photodetectors in the blue range, unlike in the infrared, this approach eliminates the need for on-chip hybrid integration of Si CMOS with III-V photodetectors. Furthermore, the efficient electroluminescence of this device makes it feasible to consider on-chip blue laser-modulator integration for a compact optical clocking scheme.