Synthesis of large-area PtSe₂ films with strongly thickness-dependent electronic properties

Han Yeh^1*, 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, email:maggieyeh15@yahoo.com.tw

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