InGaAs-InP Quantum Wire Stark Effect Modulators: Effect of Wire Width in the Optimization of Changes in Excitonic Absorp
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InGaAs-InP Quantum Wire Stark Effect Modulators: Effect of Wire Width in the Optimization of Changes in Excitonic Absorption and Index of Refraction
M. Xu, Microsoft Corp., 15400 NE 13th Pl, Bellevue, WA 98007 W. Huang, Electrical Engineering and Computer Science Department United State Military Academy, West Point, NY 10996 F. Jain, Department of Electrical and Computer Engineering University of Connecticut, Storrs, CT 06269-2157
Abstract Quantum wire/dot modulators offer superior performance over their quantum well counterpart due to enhanced excitonic binding energy. This paper presents simulations on InGaAs-InP quantum wire Stark effect optical modulators showing a novel trend. While the excitonic binding energies and absorption coefficients increase as the width of the wire is decreased, the refractive index change ∆n is maximized at a wire width depending on the magnitude of the applied electric field. For example, ∆n is maximized at a width of about 100Å for an external electric field of 120kV/cm in an InGaAs quantum wire. This behavior is explained by considering the opposing effects of the wire width on binding energy and changes in the electron-hole overlap function in the presence of an external electric field. Practical InGaAs-InP modulators using V-groove structures are also presented.
Introduction Changes in the optical absorption and index of refraction in quantum well layers have been extensively investigated for electroabsorptive and electrorefractive modulators employing quantum confined Stark effect, QCSE [1-2]. There is a significant interest in enhancing optical gain in lasers and electrooptic effects for modulators using quantum wire structures [3-5]. Recently, Arakawa et al. [5] investigated GaAs quantum wires using V-grooves, fabricated via selective epitaxial layers through SiO2 masks. This paper computes absorption coefficient and refractive index changes in In0.33Ga0.67As-InP quantum wires involving exciton transitions resulting in Stark Effect electrooptic and electrorefractive modulators [6]. The exciton binding energies and electric field induced refractive index changes are found to be significantly higher compare to InGaAs based quantum well system [7]. In general, the narrower the wire width, the higher the exciton binding energy, thus the larger the index change due to electric field. However, our simulation indicates that the index of refraction change is maximized at a wire width of 100Å. This is due to the opposing effects of the wire width on binding energy and on the changes of electron-hole overlap functions due to electric field.
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Exciton binding energy InGaAs-InP quantum wire modulators
Fig. 1 shows the cross-sectional schematic of an In0.33Ga0.67As-InP multiple quantum wire structure. This device can be grown using MOCVD via selective area epitaxy through a SiO2 mask, forming quantum wires in the bottom of V-grooves (similar to the work of Arakawa et al. [5]). Quantum confinement of electrons and holes is achieved using InP or InGaAsP lattice-matched barrier
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