Coupled InGaAs Quantum Dots for Electro-Optic Modulation

We investigated the growth of vertically coupled In0.75Ga0.25As quantum dots (QDs) by varying the GaAs spacer thickness (d). Vertically-aligned triple-layer QDs of uniform size and highest accumulated strain are formed with d = 5 nm. The electroluminescence (EL) characteristics for In0.75Ga0.25As QDs show an emission spectrum at optical wavelength (λ) of 1100−1300 nm. The EL spectra exhibit the highest optical gain at λ ~ 1200 nm, and the narrowest FWHM = 151 nm of the sample with d = 5 nm at injection current = 20 mA. Fabry–Perot measurements at λ = 1515 nm of TE and TM polarizations were carried out to investigate the electro-optic modulation for a single-mode ridge waveguide consisting of vertically-coupled triple-layer In0.75Ga0.25As QDs (d = 5 nm). The linear (r) and quadratic (s) electro-optic coefficients are r = 2.99 × 10−11 m/V and s = 4.10 × 10−17 m2/V2 for TE polarization, and r = 1.37 × 10−11 m/V and s = 3.2 × 10−17 m2/V2 for TM polarization, respectively. The results highlight the potential of TE/TM lightwave modulation by InGaAs QDs at photon energy below energy band resonance.