Electrical properties and memory effects of pure and Cr-doped WSe2

• Main Authors: Lee, Hsin-Hsien, 李信賢
• Other Authors: Jian, Wen-Bin
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/t6r87h

碩士 === 國立交通大學 === 電子物理系所 === 105 === WSe2, a two-dimensional and layered semiconducting material, attracts much attention in recent years. Scientists argued that single-layer WSe2 may have high potential for electronic and optoelectronic applications due to its high on/off ratio (as high as 106) and its direct band gap of 1.6 eV. Therefore, many research groups investigated deeply the electrical and photoelectric properties of WSe2. On the other hand, electrical properties of Cr doped WSe2 were not well studied yet. Here we will compare electrical properties, including electron transport, mobility scattering mechanisms and memory effects, of pure and Cr-doped WSe2. The field effect transistor (FET) devices of pure WSe2 show a typically n-type conducting behavior with a high current on/off ratio as high as 107. However, after doped with Cr ions, the conducting behavior changes from a n-type to an ambipolar behavior and the current on/off ratio decreases to be about 102. In addition, after Cr doping, the mobility decreases from 7 cm2/V-s to 9.7×10-3 cm2/V-s with increasing doping concentrations. The temperature dependent mobility presents a transition from a phonon scattering to an impurity scattering mechanism for heavily Cr-doped WSe2. Electron transport of pure WSe2 and Cr-doped WSe2 is studied in the temperature range from 80 to 300 K. For pure WSe2, it shows a metal-insulator transition at back-gate voltages from 20 to 70 V at temperature below 260 K. For the Cr-doped WSe2, two different conducting behaviors are observed in the temperature range from 200 to 260 K. At temperature below 200 K, the Cr-doped WSe2 show an insulating behavior and electron transport is described by Mott’s two-dimensional variable range hoping (2D-VRH). However, the characteristic temperature (T0), estimated from fitting with the 2D-VRH theory, as a function of carrier concentration does not show a rational behavior. Finally, we investigate the memory effect in either pure WSe2 or Cr-doped WSe2. For the memory device operation, we demonstrate two states of “Program” and “Erase” and present the switching between the two states by applying a back-gate voltage for a short period of 0.1 s. Both of the “Program” and the “Erase” state can be maintained for at least 2000 s. We define IE as the reading current of the “Erase” state and IP as the reading current of the “Program” state. The IE/IP ratio is used to identify the separation of the “Program” and the “Erase” states. The IE/IP ratio is reduced from a factor of 100 to 1.96 when the Cr-doping concentration is increased from 0 to 20%.