Abstract
In semiconductors, addition or subtraction of carriers can produce large changes in absorption Δα and refractive index Δn. Electron-hole recombination times limit application of these effects in waveguide intensity modulators using current injection to modulation below ~100 MHz.1 While field effect transistor (FET) structures are capable of multigigahertz optical modulation, the metal gate is lossy and can control the absorption of only one thin channel, thus limiting the modulation depth available in a waveguide.2 We utilize a novel band gap engineered barrier, reservoir, and quantum well electron transfer structure (BRAQWETS)3,4 to achieve waveguide intensity modulators that are capable of high speed high contrast ratio operation. In each BRAQWETS, the applied voltage causes rapid electron transfer across a 200-Å spacer between a highly doped reservoir layer and a quantum well (QW), quenching the QW absorption. Frequency response is limited only by device capacitance. In addition, more than one BRAQWETS can be stacked to form the core of an n-i-n waveguide to increase modulation depth.
© 1990 Optical Society of America
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