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Tensile-strained multiple quantum well electroabsorption modulators
Abstract
A new effect leading to enhanced electroabsorption in quantum wells under biaxial tension is investigated through theoretical models and spectroscopic experiments. This effect is the electric field-induced merging of the light- and heavy hole absorption edges in an initially "light-hole-up" quantum well. The "absorption-edge-merging" or AEM effect is demonstrated for the first time through low temperature photocurrent spectroscopy. The modulation performance of reflection multiple quantum well (MQW) modulators with tensile-strained active regions utilizing AEM is compared with lattice-matched GaAs-Al$\sb{0.35}$Ga$\sb{0.65}$As modulators designed to operate over the same wavelength range. A theoretical model of electroabsorption in strained quantum wells is developed first. A variational trial function approach is used in conjunction with a Rayleigh-Ritz procedure in calculating the electronic structure of strained quantum wells. The electric-field dependent excitonic and interband absorption coefficients are then calculated. Calculations showing the AEM and electroabsorption enhancement for In$\sb{x}$Ga$\sb{1-x}$As-InP and GaAs$\sb{x}$P$\sb{1-x}$-Al$\sb{0.35}$Ga$\sb{0.65}$As are then described. Tradeoffs involving the advantages of AEM are identified through theoretical comparisons of tensile-strained modulators with analogous lattice-matched structures. Optimal structures for operation at 1.55$\mu$m in In$\sb{x}$Ga$\sb{1-x}$As-InP and 0.77$\mu$m in GaAs$\sb{x}$P$\sb{1-x}$-Al$\sb{0.35}$Ga$\sb{0.65}$As are identified and the sensitivity of their electroabsorption characteristics to material and structural parameters are examined. The experimental studies of the AEM effect are considered next. The field-induced merging of the electron-to-light hole (e-lh) and electron-to-heavy-hole (e-hh) excitonic absorption edges in tensile-strained quantum wells is demonstrated. Photocurrent spectra at 77K of a 95A GaAs$\sb{0.92}$P$\sb{0.08}$-Al$\sb{0.37}$Ga$\sb{0.63}$As MQW structure embedded in a p-i-n diode show reduction and eventual elimination of a zero-bias $\sim$ 7meV splitting between the e-lh and e-hh exciton peaks with increasing reverse bias. The modulation performance tensile-strained GaAs$\sb{x}$P$\sb{1-x}$ -Al$\sb{0.37}$Ga$\sb{0.63}$As reflection modulators is then compared to that of similar lattice-matched GaAs -Al$\sb{0.37}$Ga$\sb{0.63}$As devices operating over the same wavelength range. The tensile strained modulators utilize 95A GaAs$\sb{0.92}$P$\sb{0.08}$-Al$\sb{0.37}$Ga$\sb{0.63}$As quantum wells, while the lattice matched devices utilize $\sim$46 A GaAs-Al$\sb{0.37}$Ga$\sb{0.63}$As quantum wells yielding similar excitonic gaps. Room temperature differential reflection spectra demonstrating increased modulation depths at low drive voltages in the tensile-strained devices are presented, consistent with theory.
Subject Area
Electrical engineering|Condensed matter physics
Recommended Citation
Gomatam, Badri Narayan, "Tensile-strained multiple quantum well electroabsorption modulators" (1993). Doctoral Dissertations Available from Proquest. AAI9408280.
https://scholarworks.umass.edu/dissertations/AAI9408280