Control of material properties with photo-induced charge transfer using negative electron affinity surface

我们一直在研究控制从半导体表面到吸附薄膜的电荷转移的新方法，这是基于我们最近利用同步辐射和激光获得的新的芯级光电子能谱以及负电子亲和表面的形成。这与表面电势的瞬变、光致电荷转移的动力学、自旋极化的电子、光致相变等重要问题密切相关。本研究的目的是将上述技术应用于半导体与智能材料的界面，控制材料的性质和自旋、性质。此外，与界面动力学相关的重要基础课题，如界面电势、非平衡动力学、光致电荷转移以及新性质的产生等。(1)本论文综述了近几年来国内外对GaAs负电子亲和面的研究。此外，我们还进行了表面光伏效应的时间分辨测量，并建立了表面光伏效应对GaAsP-GaAs超晶格的动力学模型。在上述研究成果的基础上，我们开展了对表面和界面上的光诱导现象的研究。在p-GaAs(100)/Cr系统上观察到了明显的变化，尽管预期会有抑制。虽然p-GaN具有较大的光效应，但表面光伏效应的光通量依赖关系并不简单，表现出反常行为。为了研究表面的快速动力学，我们还测试了由强飞秒激光器和稀有气体室组成的新系统。新的显微镜系统正在建设中。

We have been investigating the new way to control the charge transfer from semiconductor surfaces to the adsorbed films, which is based on our recent achievement of the new core-level photoelectron spectroscopy using, synchrotron radiation and laser light and also of the formation for, the negative-electron affinity surfaces. This is closely related the important problems such as transient change in the surface potential, dynamics of the photo-induced charge transfer, spin-polarized electrons, photo-induced phase transitions.The purpose of the present study is to apply the techniques mentioned above for the interface between the semiconductors and intelligent materials and control the material properties and spin,characters. Moreover, the important basic subjects related to the interfacial dynamics such as interfacial potential, non-equilibrium dynamics, photo-induced charge transfer, and production of new properties.(1)In this year, we have summarized the negative electron amity surfaces on GaAs. Also we have conducted the time-resolved measurements of surface photo-voltage effect and constructed the dynamical model for surface photo-voltage effects on GaAs and GaAsP-GaAs superlattices. The results have been published in the journals.(2)Based on the above results, we have developed our studies to the photo-induced phenomena on surfaces nad interfaces. The appreciable change was observed on p-GaAs(100)/Cr system in spite of the expectation for the suppression. Although the large photo-effect is expected on p-GaN, the photon-flux dependence of the surface photovoltage effect is not simple and shows the anomalous behavior. The analyses are under progress.(3)In order to investigate the fast dynamics of the surfaces, we have also been testing the new system consisted of an intense femt-second laser and a rare-gaseous chamber. The new microscopy system is under construction.