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Abstract Semiconductor heterojunctions are ubiquitous components of modern electronics. Their properties depend crucially on the band alignment at the interface, which may exhibit straddling gap (type-I), staggered gap (type-II) or broken gap (type-III). The distinct characteristics and applications associated with each alignment make it highly desirable to switch between them within a single material. Here we demonstrate an electrically tunable transition between type-I and type-II band alignments in MoSe2/WS2heterobilayers by investigating their luminescence and photocurrent characteristics. In their intrinsic state, these heterobilayers exhibit a type-I band alignment, resulting in the dominant intralayer exciton luminescence from MoSe2. However, the application of a strong interlayer electric field induces a transition to a type-II band alignment, leading to pronounced interlayer exciton luminescence. Furthermore, the formation of the interlayer exciton state traps free carriers at the interface, leading to the suppression of interlayer photocurrent and highly nonlinear photocurrent-voltage characteristics. This breakthrough in electrical band alignment control, interlayer exciton manipulation, and carrier trapping heralds a new era of versatile optical and (opto)electronic devices composed of van der Waals heterostructures.
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Band alignments, conduction band edges and intralayer bandgap renormalisation in MoSe 2 /WSe 2 heterobilayers
Abstract Stacking two semiconducting transition metal dichalcogenide (MX2) monolayers to form a heterobilayer creates a new variety of semiconductor junction with unique optoelectronic features, such as hosting long-lived dipolar interlayer excitons. Despite many optical, transport, and theoretical studies, there have been few direct electronic structure measurements of these junctions. Here, we apply angle-resolved photoemission spectroscopy with micron-scale spatial resolution (µARPES) to determine the band alignments in MoSe2/WSe2heterobilayers, usingin-situelectrostatic gating to electron-dope and thus probe the conduction band edges. By comparing spectra from heterobilayers with opposite stacking orders, that is, with either MoSe2or WSe2on top, we confirm that the band alignment is type II, with the valence band maximum in the WSe2and the conduction band minimum in the MoSe2. The overall band gap isEG= 1.43 ± 0.03 eV, and to within experimental uncertainty it is unaffected by electron doping. However, the offset between the WSe2and MoSe2valence bands clearly decreases with increasing electron doping, implying band renormalisation only in the MoSe2, the layer in which the electrons accumulate. In contrast,µARPES spectra from a WS2/MoSe2heterobilayer indicate type I band alignment, with both band edges in the MoSe2. These insights into the doping-dependent band alignments and gaps of MX2heterobilayers will be useful for properly understanding and ultimately utilizing their optoelectronic properties.
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- Award ID(s):
- 2308979
- PAR ID:
- 10544495
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- 2D Materials
- Volume:
- 11
- Issue:
- 4
- ISSN:
- 2053-1583
- Format(s):
- Medium: X Size: Article No. 045021
- Size(s):
- Article No. 045021
- Sponsoring Org:
- National Science Foundation
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