| Research Abstract |
Electric field control of 2-dimentional excitons in quantum well structures is very attractive from the viewpoint of both physics and application to new functional opto-electronic devices. In conventional type I quantum well structures, the exciton peak shifts toward the longer wavelength with applying an electric field, which is well known as the quantum confined Stark effect(QCSE). This effect was applied for a new type of opto-electronic devices, such as a self-electro-optic effect device(SEED), and a high-efficient multiple quantum well(MQW)optical modulator in optical fiber communication systems. Introduction of asymmetric structure of the quantum well structure will make it possible to get further enhancement of the electric field effect of the excitons, because of a large change of wavefunction overlap of electrons and holes by the applied electric field. In this study, we proposed an In_<0.53>Ga_<0.47>As/GaAs_<0.5>Sb_<0.5>/In_<0.52>Al_<0.48> asymmetric type II MQW structure lat
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tice-matched to InP substrates, which was successfully grown by molecular beam epitaxy(MBE). The InGaAs/GaAsSb/InAlAs asymmetric type II MQW structures were grown on Fe doped(100)InP substrates by solid source MBE.In this experiment, the thickness of the InGaAs layer and the InAlAs layer was fixed to 70Å and GaAsSb layer thickness is varied from 0Å to 70Å. It is known that the MQW layer is completely lattice-matched to InP substrate and a symmetric diffraction pattern was obtained. The sharp satellite peaks indicate small composition fluctuation and structural fluctuation in the grown layer. The samples show n-type with the electron concentration of 2x10^<15> cm^<-3> and the electron mobility of 3700 cm^<-2>/v.s at 300K.They were characterized by photoluminescence(PL) measurements and optical absorption measurements. Photoluminescence and optical absorption measurements were carried out in order to clear the fundamental characteristics of the grown layers. It was found that the emission wavelength changes from 1.4 μm to 2.5 μm with increasing the GaAsSb layer thickness from 0Å to 70Å, and the GaAsSb thickness dependence of the emission energy agrees fairly well with the calculation. In addition, a clear excitonic absorption at 1.5μm was observed at 300K in this new type of MQW structures. Less
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