Device Physics of Strongly Correlated Semiconductor

本研究项目的目的是探索强关联半导体的器件物理。主要目标之一是杂质效应。作为一个典型的系统，轻掺杂的Mott绝缘体Ca_<2-x>Na_xCuO_2Cl_2进行了研究。我们发现了与STM/STS掺杂相关的电子的非标度自组织，并最终将其确定为棋盘式电荷有序，我们认为这是铜酸盐物理学的核心，包括大的假能隙现象。我们还发现了近铁磁双烯酸盐中杂质周围电子态的纳米尺度变化，这代表了在强关联电子系统中建立杂质态物理的重要一步。另一个主要目标是制造氧化物器件，特别是场效应晶体管（FET）。我们已经成功地制备了SrTiO_3钙钛矿FET，它表现出良好的FET特性，如漏电流饱和。在另一种钙钛矿氧化物KTaO_3中获得了更好的性能，其显示出1000的开/关比和0.4 cm^2/Vsec的场效应迁移率，与有机FET相当。这些器件可以在低温2K下工作，并证实了金属通道的存在。这些结果为外来过渡金属氧化物的FET“化学”打开了大门。

The aim of this research project is to explore the device physics of strongly correlated semiconductors. One of the major targets was the impurity effect. As a prototypical system, lightly doped Mott insulator Ca_<2-x>Na_xCuO_2Cl_2 was studied. We found a non-scale self-organization of electrons associated with doping by STM/STS and finally identified it as a checkerboard type charge ordering, which we believe is at the heart of cuprate physics including large psedo-gap phenomena. We also find nano-scale variation of electronic states around the impurities in nearly ferromagnetic ruthenates, which represents an important step to establish physics of impurity states in strongly correlated electron systems. The other major targets was fabrication of oxide device, in particular field effect transistor (FET). We have successfully fabricated SrTiO_3 perovskite FET, which shows well defined FET characteristics such as the saturation of drain current. Even better performance was achieved in another perovskite oxide KTaO_3, which showed ON/OFF rationof 1000 and the field effect mobility of 0.4 cm^2/Vsec comparable with those of organic FET. These devices can work at a cryogenic temperature as low as 2K and the presence of metallic channel was confirmed. These results opened door for FET "chemistry" of exotic transition metal oxides.