Device Physics of Strongly Correlated Semiconductor

本研究项目的目的是探索强相关半导体的器件物理。其中一个主要目标是杂质效应。以轻掺杂Mott绝缘子Ca_<2-x>Na_xCuO_2Cl_2为原型体系进行了研究。我们发现了与STM/STS掺杂相关的电子的非尺度自组织，并最终将其确定为棋盘型电荷有序，我们认为这是铜物理的核心，包括大伪间隙现象。我们还发现了近铁磁性钌酸盐中杂质周围电子态的纳米级变化，这是建立强相关电子系统中杂质态物理学的重要一步。另一个主要目标是氧化物器件的制造，特别是场效应晶体管（FET）。我们成功地制备了SrTiO_3钙钛矿场效应管，该场效应管具有良好的特性，如漏极电流饱和。另一种钙钛矿氧化物KTaO_3的性能更好，其ON/OFF比为1000，场效应迁移率为0.4 cm^2/Vsec，与有机场效应管相当。这些器件可以在低至2K的低温下工作，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场效应管“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.