Quantum Structure Long-wavelength Light Emitting Devices Using Heterojunction Energy Filters

对化合物半导体量子结构中子带间光跃迁的基本性质进行了研究，以获得利用子带间光跃迁实现长波发光器件所需的理解。从理论上研究了以下两种量子结构，并证明它们都可以用于实现长波LED:(1) InAs/AlSb/GaSb量子结构，其中所有通过该结构的电子都经历子带间跃迁；(2)利用更成熟的AlGaAs/GaAs体系的能量滤波结构。即使在光学声子的快速非辐射弛豫下，这两种结构也能实现种群反转。在实验方面，生长了AlGaAs/GaAs结构，并测量了电场作用下的亚带间吸收，以阐明电场对跃迁的影响。研究发现，当阱中载流子浓度较高时，吸收能向低能方向移动，而当载流子浓度较低时，吸收能向高能方向移动（Stark位移）。基于这些结构的子带间跃迁，实验正在进行中。

Research on the basic properties of the inter-subband optical transition in compound semiconductor quantum structures was carried out to gain the understanding required to realize long-wavelength light emitting devices utilizing the inter-subband optical transitions.The following two quantum structures were investigated theoretically and both are shown to be able to be used to realize long-wavelength LED's : (1) InAs/AlSb/GaSb quantum structures in which all the electrons pass through the structure undergo inter-subband transition, and (2) energy filter structures utilizing more mature AlGaAs/GaAs systems. Population inversion was also shown to be realized by the two structures even under the fast nonradiative relaxation by optical phonons.On the experimental side, AlGaAs/GaAs structures were grown and the inter-subband absorption under electric fields was measured to clarify the effect of electric field on the transition. It was found that the absorption energy shifted toward low energy when carrier concentration in the well was high, whereas it shifted toward high energy when carrier concentration was low (Stark shift).Experiments are under way to experimentally realize the LED's based on the inter-subband transitions in these structures.