Energy Band Alignment of a Monolayer MoS2 with SiO2 and Al2O3 Insulators from Internal Photoemission

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Internal photoemission of electrons (IPE) from large area one monolayer 2H-MoS 2 films synthesized on top of amorphous (a−) SiO 2 or Al 2 O 3 is used to determine the energy of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). This allows us to compare the VB top energy in MoS 2 to that of the (100)Si substrate crystal at the interface with the same insulator. Despite the CB in a–Al 2 O 3 is found to be ≈1 eV below that in SiO 2 as measured relative to the Si VB edge, the authors observe nearly no shift of the spectral threshold in the case of IPE from the MoS 2 VB. This observation indicates violation of electroneutrality at the MoS 2 /a–Al 2 O 3 interface causing an increase in barrier by ≈1 eV. This conclusion is supported by the much weaker field dependence of the IPE threshold at the MoS 2 /a–Al 2 O 3 interface compared to the MoS 2 /a–SiO 2 one, suggesting the presence of negative charges and/or interface dipoles. Therefore, the commonly accepted electron affinity rule (EAR) appears to be not appropriate to describe the band alignment at 2D/insulator interfaces.

Publication year:2019

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CSS-citation score:1

Authors:International

Authors from:Higher Education

Accessibility:Open