Investigation of SnSe₂/WSe₂/h-BN Heterostructure field-effect transistors with graphene contacts

• Main Authors: Yi-Yun Yao, 姚懿耘
• Other Authors: Yuen-Wuu Suen
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5759004%22.&searchmode=basic

碩士 === 國立中興大學 === 奈米科學研究所 === 107 === We investigate two-dimensional (2D) material heterostructures by scanning photocurrent microscopy (SPCM). By using mechanical exfoliation and dry transfer method, we fabricate the heterojunction devices consisting of three different layered materials SnSe2, WSe2 and h-BN on the Si substrates with 300 nm SiO2. Different stacking order of WSe2 and SnSe2 was tested. The size of the overlapped region of the samples are all over 5x5 μm^2, and the values of W and L of are in the range of few μm and tens of μm. The Ti/Au(20nm/80nm) electrodes were defined by e-beam lithography. The device exhibits an ON/OFF ratio ~106 at VDS = 1V. The best subthreshold swing (SS) obtained from the IDS-VGS transfer curve at VDS = 1V is about 0.44 V/dec. The SS under certain bias conditions is temperature independent; this indicates that the tunneling current is dominant. The scanning photocurrent microscopy (SPCM) technique is used to study the spatial dependent photo-response of the device. A 532nm laser, which can excite both of SnSe2 and WSe2, with a spot size of about 1.5 μm is focused on the sample and scanned by a nano-positioner. The scanning step is 0.05 μm. The photocurrent is mainly within the WSe2 and SnSe2 heterostructure. The photocurrent is close to zero for VGS > 40V. It indicates that the SnSe2/WSe2 junction possesses a type III band alignment under the illumination condition.