Computing and communication systems are expected to become increasingly dependent upon optical and optoelectronic device technologies to support future bandwidth requirements. Compound semiconductor materials, such as AlGaAs or InGaAsP, can be used to implement many of these photonic devices, including lasers, modulators, optical switches, optical amplifiers, and photodetectors. For absorptive semiconductor devices such as electroabsorption modulators, saturable absorbers and photodetectors, the maximum operating speed or pulse repetition rate is often limited by the lifetime of the photo-excited carriers, which can be as long as nanoseconds in standard material. The carrier lifetime can be reduced through a number of techniques including ion implantation, impurity doping, and low-temperature (LT) growth.
This research is focused on the design and characterization of low-temperature-grown InGaAs/InAlAs quantum-well materials and devices for use in the 1.55-micron low-loss fiber window. Time-resolved differential transmission (pump/probe) measurements demonstrate that the photo-excited carrier lifetime in this material system is reduced from >100 ps to <1 ps through LT growth. This ultrafast recovery time makes this material potentially useful for high-speed (>100 Gb/s) optical communication systems. Devices currently being developed using this material include saturable absorbers for mode-locked lasers and high saturation-intensity electroabsorption modulators. This research is being performed in collaboration with Purdue University's MRSEC for Technology Enabling Heterostructure Materials.
Publications & Presentations
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S. E. Ralph, M. C. Hargis, P. W. Juodawlkis, C. M. Verber, P. Chin, and J. M. Woodall, "Femtosecond optical nonlinearities of low-growth temperature InGaAs multiple quantum wells," presented at the American Physical Society Annual Meeting, St. Louis, MO, 1996. |
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S. E. Ralph, M. C. Hargis, P. W. Juodawlkis, C. M. Verber, P. Chin, and J. M. Woodall, "Picosecond optical response of low growth temperature InGaAs/InAlAs multiple quantum wells," presented at the International Quantum Electronics Conference (IQEC), Sydney, Australia, 1996. |
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P. W. Juodawlkis, D. T. McInturff, and S. E. Ralph, "Ultrafast carrier dynamics and optical nonlinearities of low-temperature-grown InGaAs/InAlAs multiple quantum wells," Appl. Phys. Lett., vol. 69, pp. 4062-4064, 1996. |
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P. W. Juodawlkis, D. T. McInturff, and S. E. Ralph, "Subpicosecond nonlinear absorption recovery dynamics of low-temperature-grown InGaAs/InAlAs multiple quantum well p-i-n structures," to be presented at the OSA Spring Topical Meeting on Ultrafast Electronics and Optoelectronics, Lake Tahoe, NV, 1997. |
For more information, contact Dr. Stephen Ralph at stephen.ralph@ece.gatech.edu.
