Synthesis of large-area PtSe2 films with strongly thickness-dependent electronic properties
Han Yeh1*, Chang-You Song1, Chia-Shuo Li2, Yi Chou1, Ming-Young Li3, Chih-I Wu2, Yi-Chia Chou1, Lain-Jong Li3, Wen-Hao Chang1
1Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan
3Corporate Research and Chief Technology Office, Taiwan Semiconductor Manufacturing Company, Hsinchu, Taiwan
* Presenter:Han Yeh,
Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have been studied intensively because of their potential applications in electronic devices. Platinum diselenide (PtSe2) has recently found as a special member of TMDs with strongly thickness-dependent electronic properties: it is a semiconductor in the monolayer limit, and becomes a semimetal as the thickness is increased to a few layers, which may solve the issue of high contact resistance commonly observed in conventional TMDs. Most of the reported experiments on PtSe2 so far are based mechanical exfoliations from bulk crystals or direct selenization from Pt film. Here we demonstrate using chemical vapor deposition (CVD) to grow uniform and large-area PtSe2 films on sapphire with controllable thickness and low surface roughness. By tuning the growth temperature and time, PtSe2 films with a thickness ranging from 0.8 to 20 nm can be grown. High-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) analyses reveal that the PtSe2 exhibit an octahedral structure (1T phase) with a typical grain size of about 10 nm. The thickness dependent work function and band gap of PtSe2 are identified by ultraviolet photoelectron spectroscopy (UPS) and Fourier-transform infrared spectroscopy (FTIR). We found that the work function of PtSe2 is increasing from 4.3 to 4.86 eV with the increasing thickness from 0.8 to 16 nm. Moreover, we observe a band gap opening for thicknesses below 2.2 nm, which is an evidence that thin PtSe2 is a semiconductor. Transfer length measurements on thick PtSe2 film show a low contact resistance (722 Ω∙μm) and a low sheet resistance (921 Ω/□), indicating good electrical properties for device applications.

Keywords: semiconducting transition metal dichalcogenides , PtSe2, contact resistance