[논문 리뷰] Mobility Improvement and Temperature Dependence in MoSe2 Field-Effect Transistors on Parylene-C Substrate

Bhim Chamlagain, Qing Li외 10명|arXiv (Cornell University)|2014. 04. 14.

Advanced Memory and Neural Computing인용 수 5

한 줄 요약

이 연구는 parylene-C 기판 상의 MoSe2 필드효과 트랜지스터가 SiO2 기판 상의 경우보다 상온에서 훨씬 높은 이동도(~100–160 cm²V⁻¹s⁻¹)를 나타내며, 100 K에서 약 ~500 cm²V⁻¹s⁻¹까지 증가함을 보여준다. 이는 parylene-C에서 표면 극성 광학 격자파 산란이 감소하여 SiO2보다 산란이 적어지기 때문이며, 표면 거칠기의 유사성에도 불구하고 이와 같은 향상이 이루어진다.

ABSTRACT

We report low temperature scanning tunneling microscopy characterization of MoSe2 crystals, and the fabrication and electrical characterization of MoSe2 field-effect transistors on both SiO2 and parylene-C substrates. We find that the multilayer MoSe2 devices on parylene-C show a room temperature mobility close to the mobility of bulk MoSe2 (100 cm2V-1s-1 - 160 cm2V-1s-1), which is significantly higher than that on SiO2 substrate (~50 cm2V-1s-1). The room temperature mobility on both types of substrates are nearly thickness independent. Our variable temperature transport measurements reveal a metal-insulator transition at a characteristic conductivity of e2/h. The mobility of MoSe2 devices extracted from the metallic region on both SiO2 and parylene-C increases up to ~ 500 cm2V-1s-1 as the temperature decreases to ~ 100 K, with the mobility of MoSe2 on SiO2 increasing more rapidly. In spite of the notable variation of charged impurities as indicated by the strongly sample dependent low temperature mobility, the mobility of all MoSe2 devices on SiO2 converges above 200 K, indicating that the high temperature (> 200 K) mobility in these devices is nearly independent of the charged impurities. Our atomic force microscopy study of SiO2 and parylene-C substrates further rule out the surface roughness scattering as a major cause of the substrate dependent mobility. We attribute the observed substrate dependence of MoSe2 mobility primarily to the surface polar optical phonon scattering originating from the SiO2 substrate, which is nearly absent in MoSe2 devices on parylene-C substrate.

연구 동기 및 목표

• To investigate the substrate-dependent mobility in MoSe2 field-effect transistors.
• To understand the origin of mobility differences between SiO2 and parylene-C substrates.
• To examine the temperature dependence of transport properties in multilayer MoSe2 devices.
• To determine whether surface roughness or polar optical phonon scattering dominates mobility suppression.
• To clarify the role of charged impurities in mobility variation at low temperatures.

제안 방법

• Fabricated MoSe2 field-effect transistors on both SiO2 and parylene-C substrates using mechanical exfoliation.
• Performed low-temperature scanning tunneling microscopy (STS) to characterize MoSe2 crystal structure and electronic properties.
• Conducted variable-temperature electrical transport measurements from 4 K to 300 K to analyze mobility trends.
• Used atomic force microscopy (AFM) to compare surface roughness of SiO2 and parylene-C substrates.
• Extracted mobility from the metallic region of the conductivity-temperature curve using the Drude model.
• Analyzed the metal-insulator transition at a critical conductivity of e²/h to identify transport regime changes.

실험 결과

연구 질문

• RQ1 Why does MoSe2 on parylene-C exhibit higher mobility than on SiO2 at room temperature?
• RQ2 How does temperature affect the mobility of MoSe2 FETs on different substrates?
• RQ3 To what extent do charged impurities or surface roughness influence mobility in MoSe2 devices?
• RQ4 What is the dominant scattering mechanism responsible for mobility degradation on SiO2 substrates?
• RQ5 Does the high-temperature mobility in MoSe2 devices depend on substrate-induced charged impurities?

주요 결과

• MoSe2 FETs on parylene-C substrates achieve room temperature mobility of 100–160 cm²V⁻¹s⁻¹, significantly higher than the ~50 cm²V⁻¹s⁻¹ observed on SiO2.
• Mobility increases to ~500 cm²V⁻¹s⁻¹ at 100 K on both substrates, with a faster rise on SiO2, indicating stronger temperature-dependent scattering effects.
• The high-temperature (>200 K) mobility is nearly independent of charged impurities, as all SiO2-based devices converge above this temperature.
• Surface roughness is ruled out as the main cause of mobility differences, as AFM shows comparable roughness on both substrates.
• The substrate-dependent mobility is primarily due to surface polar optical phonon scattering, which is strong on SiO2 but nearly absent on parylene-C.
• A metal-insulator transition is observed at a critical conductivity of e²/h, confirming the presence of a quantum phase transition in the system.