Abstract
Wafer-scale synthesis of p-type TMD films is critical for its commercialization in next-generation electro/optoelectronics. In this work, wafer-scale intrinsic n-type WS2 films and in situ Nb-doped p-type WS2 films were synthesized through atomic layer deposition (ALD) on 8-inch α-Al2O3/Si wafers, 2-inch sapphire, and 1 cm2 GaN substrate pieces. The Nb doping concentration was precisely controlled by altering cycle number of Nb precursor and activated by postannealing. WS2 n-FETs and Nb-doped p-FETs with different Nb concentrations have been fabricated using CMOS-compatible processes. X-ray photoelectron spectroscopy, Raman spectroscopy, and Hall measurements confirmed the effective substitutional doping with Nb. The on/off ratio and electron mobility of WS2 n-FET are as high as 105 and 6.85 cm2 V−1 s−1, respectively. In WS2 p-FET with 15-cycle Nb doping, the on/off ratio and hole mobility are 10 and 0.016 cm2 V−1 s−1, respectively. The p-n structure based on n- and p- type WS2 films was proved with a 104 rectifying ratio. The realization of controllable in situ Nb-doped WS2 films paved a way for fabricating wafer-scale complementary WS2 FETs.
Highlights
As silicon-based CMOS technology is reaching its physical limits, two-dimensional transition metal dichalcogenides (TMDs) have been intensively investigated as potential ultrathin channel materials for future electronics
Chemical vapor deposition (CVD) is an effective way to synthesize singlecrystalline TMDs films [15,16,17], but wafer-scale deposition and precisely-controlled thickness of TMDs films are difficult to achieve via CVD
Because TMD films are too thin for p-type doping by ion implantation [18,19,20,21], a variety of different approaches have been pursued, including charge transfer doping by physical adsorption of molecules or salts on surface [22,23,24,25], and metal oxides (MoO3) [26] or metalinduced inversion (Tungsten) [27, 28] of WS2 through interfacial interactions
Summary
As silicon-based CMOS technology is reaching its physical limits, two-dimensional transition metal dichalcogenides (TMDs) have been intensively investigated as potential ultrathin channel materials for future electronics. There are still many challenges, including (1) realization of large wafer-scale deposition, (2) a controllable p-type doping method for TMD films, (3) reducing Schottky barrierinduced Fermi level pinning at the metal/TMDs contacts, and (4) high-quality high-k/TMD interface. Chemical vapor deposition (CVD) is an effective way to synthesize singlecrystalline TMDs films [15,16,17], but wafer-scale deposition and precisely-controlled thickness of TMDs films are difficult to achieve via CVD. It has proven difficult to precisely control the doping behaviors and electronic device performance
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