Study on the Electrooptic Properties of Semiconductor Heterojunction and Their Application to Optical Modulation

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(1)Fabrication of double-hetero and quantum well structures by molecular beam epitaxy (MBE) A new MBE system, which utilize the modern control theory for temperature control, has been constructed. Techniques for the fabrication of the double-hetero and quantum well structures with good reproducibility has been established.(2)GaAs-based directional coupler type optical modulators by use of the linear electrooptic effect Design and fabrication of a traveling-wave type device have been performed to obtain the higher switching speed of the GaAs-based directional coupler type optical modulators. The 8mm-long sample, with a switching voltage of 10.4V and a modulation bandwidth of 9.lGHz at a wavelength of 1.06mum, has been successfully fabricated for the first time. A semiconductor-based polarization-independent directional coupler type optical modulator, on a (111) substrate instead of the conventional (100), has also been proposed and designed.(3)Carrier-injection type optical modulator wi … More th bipolar transistor structure Theoretical analyses on the characteristics, such as absorption loss, extinction ratio and chirping parameters, of the bipolar transistor carrier-injection type optical modulator have been performed in detail , and the advantage of the device has been revealed. An MBE-grown single-guide type optical intensity modulator with fairly good performance has been successfully fabricated for the first time. On the basis of the result, it has been found that the bipolar transistor structure is applicable to an X-cross total reflection type optical switch.(4)Electric field induced effect in quantum well waveguides An absorption type optical modulator by use of the quantum confined Stark effect, with an extinction ratio of 13dB at 5.5V bias operating at 880nm, has been fabricated. In addition, modifications in quantum confinement structures, which may provide the optical modulation devices with high performance and various functions, have been investigated both theoretically and experimentally. Some interesting properties in a graded-gap quantum well, a parabolic quantum well and a coupled quantum well have been confirmed. (5)Carrier induced effect in a quantum well A band filling effect by two-dimensional electrons, a band gap shrinkage effect by the many body effect of electrons and their magnetic field induced effects have been studied in detail through carrier injection into a GaAs / AlGaAs single quantum well structure. In addition, changes in the physical constants. such as the refractive index, which are induced by the phenomena described above, have been also investigated, and found to be applicable to the optical modulation devices. Less