n‐Type Doping Effect of CVD‐Grown Multilayer MoSe₂ Thin Film Transistors by Two‐Step Functionalization

Abstract

Molybdenum diselenide (MoSe2) has attracted attention as a potential semiconductor platform. However, the as‐synthesized MoSe2 field‐effect transistors (FETs) tend to exhibit the arbitrary properties of n‐type, p‐type, or ambipolar behavior due to the uncontrolled growth condition. Here, two‐step functionalization is proposed to achieve n‐doping effect and long‐term stability in chemical vapor deposition (CVD)–grown MoSe2 FETs using oxygen plasma treatment followed by the deposition of an Al2O3 layer. After the two‐step surface functionalization procedure, three types of multilayer MoSe2 FETs are all converted to n‐type with the improvement of their electrical characteristics and stability; the n‐doped multilayer MoSe2 FETs exhibit an enhancement in field‐effect mobility from 12.23 to 31.57 cm2 V−1 s−1 and a 3 times higher Ion/Ioff, compared to pristine multilayer MoSe2 FETs. This enhancement of electric performance is attributed to the oxidation of topmost MoSe2 to interfacial MoOx with SeOx induced by the oxygen plasma treatment, as well as to the existence of fixed positive charges in deposited Al2O3. The functionalized devices exhibit excellent stability against stress, as confirmed with negative bias illumination stress tests for 7200 s. Moreover, an environmental stability test for 21 days reveals no degradation in electric performance of MoSe2 FETs.

Ambipolar 2D Semiconductors and Emerging Device Applications

“…Through optimizing the growth conditions, single crystal 2D WSe 2 could reach up to 165 µm wide. [90] Besides WSe 2 , many efforts have been made on other ambipolar 2D materials like MoS 2 , [91][92][93][94] WS 2 , [95] MoSe 2 , [96][97][98][99][100] and even ternary compounds. [101] Both of MoS 2 and MoSe 2 have been achieved scalable growth.…”

Recent Advances in Electrical Doping of 2D Semiconductor Materials: Methods, Analyses, and Applications

“…By simply coating or depositing a film that provides a doping effect, the electrical properties of the TMDs, such as effective mobility, threshold voltage, and subthreshold swing, can be adjusted. This approach enables forming a heterostructure of the doping film and the TMD, in which the electrical or optical characteristics of the TMDs can be enhanced by (i) charge transfer from the dopant molecules to TMDs [ 62 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 ] or (ii) dipole effects of the dopant molecules of the doping film [ 4 , 5 , 6 , 7 , 93 , 94 , 95 ]. The energy band structure of MoS 2 could be controlled through molecular doping from the deposited tetrathiafulvalene and dimethyl-phenylenediamine molecules as donors and tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) as acceptors ( Figure 6 a,b) [ 72 , 88 ].…”

“…To provide high-stable doping effects, a two-step functionalization doping scheme was developed. The two-step n-doping process based on oxygen plasma treatment and Al 2 O 3 deposition allowed MoSe 2 transistors to operate as unipolar n-doped behavior, and the negative bias illumination stress (nbis) test for 7200 s and the environmental stability test for 21 days showed unchanged stable doping effect ( Figure 7 e) [ 91 ]. Although the molecular doping techniques have been intensively studied for control of the TMD devices, uniformity and controllability still remain as challenging issues.…”

“…( d ) Transfer characteristics of PDPP3T-doped MoSe 2 as a function of annealing temperature (adapted from [ 93 ] with permission from John Wiley and Sons). ( e ) Comparison of shifts in V TH derived from NBIS test results (adapted from [ 91 ] with permission from John Wiley and Sons).…”

Interfacial Doping Effects in Fluoropolymer-Tungsten Diselenide Composites Providing High-Performance P-Type Transistors

“…The high annealing temperature causes molecular aggregation in Cytop, providing a strong p-type doping effect due to the higher density of the C–F dipole domains [ 15 , 16 ]. Furthermore, Cytop prevents the penetration of moisture and other contaminants into the F-WSe 2 devices [ 17 ]. As a result, the observed p-doping effect is effectively maintained with negligible changes.…”