Lateral Quantum-Confined Stark Effect for Integrated Quantum Dot Electroabsorption Modulators

Advances in III-V on Si quantum dot (QD) growth have enabled monolithic integration of high-performance electrically-pumped lasers on Si, as an enabling component for Si photonics. Another critical component is the electroabsorption modulator (EAM), which exploits the quantum-confined Stark effect (QCSE) to achieve high-speed modulation of laser signals. Conventional quantum well (QW) EAMs exploit a “vertical” QCSE via top and bottom electrical contacts. Rapid advancements in planar photonic integrated circuit technology motivate development of laterally-contacted EAMs, which offer benefits including reduced parasitic capacitance. The QCSE cannot be achieved via a lateral field in a QW, but can in a QD due to the three-dimensional carrier confinement. Here, theoretical analysis of the lateral-field QCSE in 1.3 <tex-math notation="LaTeX">μ</tex-math>m In<tex-math notation="LaTeX">ₓ</tex-math>Ga<tex-math notation="LaTeX">₁₋ₓ</tex-math>As/GaAs QDs is undertaken. Comparing the QCSE produced by vertical and lateral electric fields for realistic QD morphology a robust lateral-field QCSE is demonstrated, with the optical absorption edge redshifting more rapidly vs. field strength than in a conventional QW-EAM. It is shown that lateral-field QD-EAM performance is expected to be strongly sensitive to the spectral linewidth of the band edge absorption, and can also depend upon the in-plane orientation of the lateral electric field. The impact of QD morphology – the base shape, aspect ratio and composition profile – is also quantified. It is demonstrated that In<tex-math notation="LaTeX">ₓ</tex-math>Ga<tex-math notation="LaTeX">₁₋ₓ</tex-math>As/GaAs QDs possessing high aspect ratios and low absorption linewidths are well-suited to develop lateral-field QD-EAMs. This suggests leveraging III-V on Si epitaxy to integrate EAMs with lasers or single-photon sources to realize high-speed Si photonic integrated circuits for applications in datacomms and linear optical quantum computing.