Tunable electrical properties of multilayer HfSe₂field effect transistors by oxygen plasma treatment

Abstract

HfSe field effect transistors are systematically studied in order to selectively tune their electrical properties by optimizing layer thickness and oxygen plasma treatment. The optimized plasma-treated HfSe field effect transistors showed a high on/off ratio improvement of four orders of magnitude, from 27 to 10, a field effect mobility increase from 2.16 to 3.04 cm V s, a subthreshold swing improvement from 30.6 to 4.8 V dec, and a positive threshold voltage shift between depletion mode and enhancement mode, from -7.02 to 11.5 V. The plasma-treated HfSe photodetector also demonstrates a reasonable photoresponsivity from the visible to the near-infrared region of light.

Large‐Area Synthesis of Layered HfS2(1−x)Se2x Alloys with Fully Tunable Chemical Compositions and Bandgaps

“…Both AFM and scanning electron microscopy (SEM) images (Figure S1, Supporting Information) show that the surface of HfSe 2 layer is rather smooth and uniform, and the root‐mean‐square (RMS) roughness determined from the AFM image is only 0.48 nm. Two characteristic Raman‐active modes of 145.8 and 198.2 cm −1 are observed in Figure e, which are in good agreement with the previously reported results of HfSe 2 . The 145.8 cm −1 peak is attributed to the E g mode, corresponding to the in‐plane vibration of Hf and Se atoms, while the 198.2 cm −1 one is the A 1g mode, arising from the out‐of‐plane vibration of Se atoms.…”

“…Similarly, Figure h shows two peaks at 53.3 and 54.2 eV representing the Se 3d 5/2 and Se 3d 3/2 core levels. All of these features are consistent with the reported values for HfSe 2 crystal . Moreover, the atomic ratio between Hf and Se obtained from the integrated peak areas is 1:1.96, suggesting that our CVD‐grown HfSe 2 possesses reasonably good stoichiometry.…”

“…Semiconducting 2D transition metal dichalcogenides (TMDs) have attracted tremendous interest in nanoelectronic and optoelectronic applications because of their unique structural characteristics, superior optical and electrical properties . Among all of TMD materials, Hf‐based monolayers and few layers, such as HfS 2 and HfSe 2 , have rarely been studied but can possess many extraordinary physical properties . For instance, the calculated room‐temperature mobility is able to reach as high as 1800 and 3500 cm 2 V −1 s −1 for HfS 2 and HfSe 2 monolayers, respectively, which are much higher than that of widely studied MoS 2 (≈340 cm 2 V −1 s −1 ) .…”

“…In spite of the superiority in theoretical prediction, comparatively limited experimental results are available probably due to the difficulty in synthesizing 2D HfSe 2 layers. Recently, back‐gated FETs were fabricated from exfoliated multilayer HfSe 2 , which exhibit an n‐type semiconductor behavior with a high on/off current ratio of 10 6 and modest mobilities lower than 10 cm 2 V −1 s −1 . Moreover, the phototransistors utilizing exfoliated few‐layered HfSe 2 as the channel material were also fabricated, which demonstrate a reasonable photoresponsivity from the visible to the near‐infrared region of light.…”

“…Recently, back‐gated FETs were fabricated from exfoliated multilayer HfSe 2 , which exhibit an n‐type semiconductor behavior with a high on/off current ratio of 10 6 and modest mobilities lower than 10 cm 2 V −1 s −1 . Moreover, the phototransistors utilizing exfoliated few‐layered HfSe 2 as the channel material were also fabricated, which demonstrate a reasonable photoresponsivity from the visible to the near‐infrared region of light. Nevertheless, all of the studies mentioned above utilized mechanically exfoliated HfSe 2 layers for device fabrication, which totally cannot control the thickness and enlarge the lateral dimension, hindering the study and practical applications of 2D HfSe 2 .…”