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

1. 为了在量子阱（QW）中获得一种新的电光效应，我们提出了一种势插入量子阱（PI-QW），其中两个耦合阱被薄的AlAs势垒隔开。PI-QWs表现出独特的场致光学效应，因为电子和空穴之间的重叠矩阵元素受到横向电场F的调制比传统QWs更强。我们通过施加F观察到吸收边的蓝移，这与通常QWs的Stark位移方向相反，显示了pi -QWs的独特特征。为了阐明载流子诱导的光学效应，我们研究了QW场效应晶体管（QW- fet）的光学特性。随着电子密度的增加，吸收边向高能量方向移动，发光峰向低能方向移动。通过与理论的比较，定量地阐明了带填充效应和多体效应。此外，我们已经证明这种载流子引起的漂白和伴随的折射率变化可以应用于光调制器和开关为了揭示复合过程是激子式的还是自由载流子式的，研究了不同电子浓度下qw - fet中光致发光的磁场依赖性。证明了载流子诱导的复合过程从激子主导过程向自由载流子主导过程的转变。此外，研究了强磁场对自由载流子复合的影响，表明在量子阱中，复合过程恢复了激子特征。高磁场，证明磁激子的形成谐振隧道结构中的载流子诱导光学效应在双势垒谐振隧道二极管（DBRTD）中，电子在谐振条件下在DBRTD的QW区积累。因此，人们期望在DBRTD中存在载流子诱导的光学效应。我们清楚地观察到在共振条件下吸收边的蓝移和光致发光能量的降低，由此可以确定累积的电子浓度。观察到的吸收蓝移表明DBRTD适用于高速光调制器和开关。少

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