Control of Optical Properties of Quantum Well Structures by Carrier Induced Effects and its Applications to Novel Optical Devices

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1. Demonstration of the field-induced blue-shift of the absorption edge in potential inserted quantum wells To get a novel electro-optic effect in quantum wells(QW), we proposed a potential inserted QWS(PI-QW), in which two coupled wells are separated by a thin AlAs barrier. PI-QWs are exhibit a unique field- induced optical effect since the overlap matrix elements between electrons and holes are more strongly modulated by the transverse electric fields F than in conventional QWs. We have observed the blue shift of the absorption edge by applying F , which is opposite in direction to the Stark shift in usual QWs, demonstrating a unique feature of PI-QWs.2.Control and clarification of carrier induced optical effect in QW structures To clarify carrier induced optical effects, we have investigated optical properties of QW field effect transistors(QW-FET). With the increase of electron density, the absorption edge shifted to higher energy and the luminescence peak shifted to lower energy. … More By comparing these observations with theory, the bandfilling and many body effect are quantitatively clarified. Furthermore, we have shown that this carrier induced bleaching and the accompanied change of refractive index can be applied to optical modulators and switches.3 Carrier-induced instability of two dimensional excitonic state and enhancement of excitonic interaction under high magnetic fields To disclose whether the recombination process is excitonic or free carrier like, the magnetic field dependence of photoluminescence is studied in QW-FETs at various electron concentration. The carrier induced transition of recombination process from excitonic to free carrier dominated process is demonstrated. In addition, the effect of high magnetic fields on free carrier recombination is studied to show that excitonic feature is recovered in recombination processes in QWs at. high magnetic fields, demonstrating the formation of magneto exciton.4 Carrier-induced optical effect in resonant tunneling structure In double barrier resonant tunneling diode(DBRTD), electrons are accumulated in the QW region of DBRTD under the resonant condition. Thus, one expects the carrier induced optical effect in DBRTD. We have observed clearly the blue shift of the absorption edge and lowering of photoluminescence energy under the resonant condition, from which the accumulated electron concentration is determined. The observed blue shift of absorption suggests the applicability of DBRTD to high speed optical modulators and switches. Less