Studies on the Optoelectronic Properties of WSe2 Thin Film Transistors

• Main Authors: Tien-Hsin Peng, 彭天欣
• Other Authors: Si-Chen Lee
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/93tyk8

碩士 === 國立臺灣大學 === 電子工程學研究所 === 107 === In this study, high-performance multilayer WSe2 filed-effect transistors were demonstrated by rapid thermal annealing process in oxygen ambient. The experimental results indicate that the field-effect mobility of hole could be enhanced from 1.49 to 31.1 cm^2/Vs after oxygen annealing treatment. The on/off-current ratio will up to so high as 10^7. It’s also used 2D-layered hexagonal-boron nitride (h-BN) as substrate or passivation layer to observe the absorbed oxygen on the channel. Additionally, it confirmed the existence of oxygen and p-doping effect after annealing treatment by measuring Raman spectra and XPS. According to the above results, both oxygen molecules on the top and at the bottom of the channel have the dramatic influence on the WSe2 TFTs’ performance, and, moreover, this work provides a method to improve the device performance of WSe2 TFTs and change the undesirable ambipolar transport to the unipolar, which is essential to the implementation of CMOS logic. Moreover, the WSe2 homostructure rectifying diode is demonstrated, p-type and n-type WSe2 regions were formed by adopting different layer WSe2 thicknesses. Typically, the common way to fabricate two-dimensional material based diode is to use heterostructure by stacking two different carrier type and band gap energies materials. However, there is always lattice mismatch at the junction, leading to the degraded photoresponse of the diodes. In order to reduce the problems of heterostructure diode, layer thickness dependent band gap energy of WSe2 is reported and applied to fabricate homostructure diode. The ideality factor of the current-voltage characteristic is 1.64 and the current rectification ratio can reach to 10^3. The optical properties of the diode, including fill factor 45.7%, responsivity 16.02 mA/W and EQE 3.06% are reported. It is concluded that the WSe2 homojunction diode can be applied in photodetectors, switches, solar cells etc.