Abstract
The encapsulation of single-layer 2D materials within hBN has been shown to improve the mobility of these compounds. Nevertheless, the interplay between the semiconductor channel and the surrounding dielectrics is not yet fully understood, especially their electron–phonon interactions. Therefore, here, we present an ab initio study of the coupled electrons and phonon transport properties of MoS-hBN devices. The characteristics of two transistor configurations are compared to each other: one where hBN is treated as a perfectly insulating, non-vibrating layer and one where it is included in the ab initio domain as MoS. In both cases, a reduction of the ON-state current by about 50% is observed as compared to the quasi-ballistic limit. Despite the similarity in the current magnitude, explicitly accounting for hBN leads to additional electron–phonon interactions at frequencies corresponding to the breathing mode of the MoS-hBN system. Moreover, the presence of an hBN layer around the 2D semiconductor affects the Joule-induced temperature distribution within the transistor.
Highlights
Substantial experimental and theoretical efforts have been invested into the development of novel channel materials that could potentially replace silicon at the end of Moore’s scaling law [1]
It has been demonstrated that the electron mobility is severely limited by surface optical phonons when a MoS2 monolayer is passivated by a high-k dielectric with low-energy polar optical phonons, as encountered in HfO2 or ZrO2 [15]
These polar optical phonon modes can be excited by the electrons in the semiconductor via long-range Coulomb interactions, which become stronger as the semiconductor thickness decreases
Summary
Substantial experimental and theoretical efforts have been invested into the development of novel channel materials that could potentially replace silicon at the end of Moore’s scaling law [1]. It has been observed that MoS2 field-effect transistors (FETs) exposed to air exhibit large shifts of their threshold voltage [5,6,7] and a profound degradation of their carrier mobility. These undesired effects, which affect both logic and analog circuit applications, can be alleviated by passivating the active semiconductor material with an oxide layer [8,9,10,11,12]. These polar optical phonon modes can be excited by the electrons in the semiconductor via long-range Coulomb interactions, which become stronger as the semiconductor thickness decreases
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