Large temperature coefficient of resistance in atomically thin two-dimensional semiconductors

Abstract

The temperature coefficient of resistance (TCR) of thin metal lines is often used for applications in thermometry, bolometers, or thermal accelerometers. However, metal TCR is much degraded in nanometer-thin films due to strong surface scattering, preventing their use as fast thermal sensors, which simultaneously require low thermal mass and large TCR. In contrast, here we show that the TCR of doped two-dimensional (2D) semiconductors is large (∼0.3% K−1 at 300 K in MoS2 and MoTe2) even at sub-nanometer thickness. This is larger than that of any metals with thicknesses up to ∼35 nm and larger than that of ∼95 nm thick Cu lines (0.25% K−1) at 300 K. At 100 K, the TCR of these 2D materials is doubled, ∼0.6% K−1. Comparison with detailed 2D transport models suggests that the TCR could be further enhanced (up to 0.45% K−1 at 300 K and ∼2.5% K−1 at 100 K) by reducing the density of Coulomb impurities and scattering centers. Such high TCR in atomically thin 2D semiconductors could lead to the design of fast thermal sensors.

Toward Low-Temperature Solid-Source Synthesis of Monolayer MoS2

“…First, comparing the effective 1L MoS 2 mobilities (μ eff , squares), we observe that our values (29 and 33 cm 2 V –1 s –1 from 560 °C growths at a reduced 490 Torr pressure) are similar to the μ eff from MoS 2 grown at higher temperatures, up to 850 °C. ,,− (Recent simulations have shown that mobilities in this range are limited by point defects, most likely, charge impurities and sulfur vacancies. , ) Field-effect mobility (μ FE ) data reported for 1L MoS 2 grown at 850 °C (lighter hollow triangles) are also included as a box-and-whisker plot (average μ FE of 34.2 cm 2 V –1 s –1 outlined in the black box), in good agreement with the 850 °C effective mobility. For CVD-grown 1L MoS 2 using solid-source precursors, our values are the highest reported mobilities to date with a thermal budget below 2 h at 600 °C.…”

“…13,16,[28][29][30] (Recent simulations have shown mobilities in this range are limited by point defects, most likely charge impurities and sulfur vacancies. 69,70 ) Field-effect mobility (µFE) data reported for 1L MoS2 grown at 850°C (lighter hollow triangles) are also included as a box-andwhisker plot (average µFE of 34.2 cm 2 V -1 s -1 outlined in the black box) 16 in good agreement with the 850°C effective mobility. For CVD-grown 1L MoS2 using solid source precursors, our values are the highest reported mobilities to date with a thermal budget below 2-hours at 600°C.…”

Uncovering the Effects of Metal Contacts on Monolayer MoS2

“…51,53 This places an upper bound on the defect density in our films, <10 13 cm −2 (interdefect distance < 3.2 nm) even after the metal deposition. A lower bound on the defect density of our asgrown films (before metal deposition) is offered by independent transport simulations, 56,57 which found an impurity density of ∼1.5 × 10 12 cm −2 (average separation ∼8 nm) when all impurities are assumed located in the MoS 2 sheet. (We note that photoluminescence can also be used to analyze defects in bare MoS 2 films, 58,59 but metal-induced nonradiative recombination can obscure this effect in our samples.…”

Photocurrent Generation Mechanisms in Molybdenum‐Contacted Semiconducting Black Phosphorus and Contributions from the Photobolometric Effect

“…Therefore, a positive contribution from the PVE and PCE mechanisms is expected in our devices using the broadband white light source which should overcome the bandgap differences in the two materials. The temperature coefficient of resistance (TCR) at 100 K for BP bolometer is about 0.17 and −0.16% K −1 at 300 K, compared with that of monolayer MoS 2 reported by Khan et al [ 50 ] which is 0.53% K −1 at 100 K and 0.27% K −1 at 30 °K. [ 50 ] Moreover, TCR of −2.9% K −1 was reported for pulsed laser deposited MoS 2 % and 900% K −1 for graphene–based pyroelectric bolometers.…”

“…The temperature coefficient of resistance (TCR) at 100 K for BP bolometer is about 0.17 and −0.16% K −1 at 300 K, compared with that of monolayer MoS 2 reported by Khan et al [ 50 ] which is 0.53% K −1 at 100 K and 0.27% K −1 at 30 °K. [ 50 ] Moreover, TCR of −2.9% K −1 was reported for pulsed laser deposited MoS 2 % and 900% K −1 for graphene–based pyroelectric bolometers. [ 51 ]…”