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UBC Theses and Dissertations

Design of SiGe/Si quantum-well optical modulators Tasmin, Tania


An electro-optic modulator containing a single SiGe/Si quantum-well has been designed for operation at λ₀= 1.55 µm. This single quantum-well modulator has a lower VπLπ than the 3 quantum-well modulator recently designed and optimized by Maine et al. for operation at λ₀= 1.31 µm, for which the VπLπ product was 1.8 V•cm [25]. Both modulators are derived from the detailed design given for their modulator in [40]. This single quantum-well modulator contains a Si₀.₈Ge₀.₂ quantum-well with Non-Intentionally Doped (NID) and P⁺ highly doped layers on either side. With no field applied, holes from the P⁺ layers are captured by and confined in the quantum-well and when a reverse bias is applied holes are released from the quantum well and drift to the P⁺ contact layer. Variations of the hole distribution lead to changes in the free-carrier absorption and the refractive index of each layer and subsequently to phase modulation of guided TE modes. The VπLπ product of the single quantum-well modulator is estimated 1.09 V•cm for low voltage linear modulation and 1.208 V•cm for 0 to 1.6 V digital modulation, whereas the 3 quantum-well modulator gives a VπLπ of 2.039 V•cm for 0 to 6 V digital modulation for operation at λ₀= 1.55 µm. Also, the optical loss in the single quantum-well (5.36 dB/cm at V=0 V) is lower than that of the 3 quantum-well structure (5.75 dB/cm at V=0 V). This single quantum-well modulator should also offer higher frequency operation than the 3 quantum-well modulator.

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