Apr 11, 2025
9:15am - 9:30am
Summit, Level 3, Room 343
Valerio Piazza1,Michele Zendrini1,Claire Blaga1,Mitali Banerjee1,Anna Fontcuberta i Morral1
Ecole Polytechnique Federale de Lausanne1
Transition metal dichalcogenides (TMDs) have high spin-orbit coupling [1], exciton funneling [2] and strain modulation [3] which may allow them to be core semiconductors in a wide variety of commercial technologies [4]. As the field expands, new concepts for nano-devices are proposed. Heterostructures made by mixing 2D and other low dimensional materials are of great interest to exploit strain and interface engineering at once [5-7]. A major bottleneck in the field is the clear understanding of nanoscale phenomena dominating the overall functionality of the ensemble. Methodologies based on secondary electron (SE) microscopy offer a great trade-off between probe size and field of view. In this framework, electron beam-induced current microscopy (EBIC) is an appealing candidate to conduct non-destructive investigation of localized electric field, thus enabling engineering of electrically active nanometric elements[8].
Here we demonstrate that EBIC mapping is a powerful method to acquire electrical maps of heterostructures with mixed dimensionality. 2D-3D WSe
2-(Al)GaAs heterostructures are fabricated via dry transfer with a PDMS stamp. Binary GaAs and ternary (Al)GaAs with Al content up to 39at.% are grown epitaxially via metalorganic vapour phase epitaxy. The epitaxial growth, performed on (100) Zn:GaAs wafers, allows to obtain both planar layers and 1D horizontal nanostructures grown by selective area method [9,10]. WSe
2 flakes with inhomogenous thickness ranging from 1-3L to around 50L are transferred on the III-V epitaxial structures. The fabricated samples are investigated by atomic force microscopy (AFM), photoluminescence (PL) and electron-beam induced current mapping (EBIC). EBIC maps of the 2D-3D heterostructures reveals an electrical built-in field in portions of the heterointerface. This evidence pinpoints the electron-rich nature of our exfoliated WSe
2, enriching the debate over the origin of free charges in ultra-thin materials. Correlated analysis with atomic force microscopy (AFM) maps evidence that the dependence of the strength of the field at the heterointerface with the thickness of the WSe
2 flake is not monotonic. On the contrary, room temperature micro-photoluminescence (PL) mapping shows increasing quenching of the epilayer emission with increasing WSe
2 thickness. Numerical modeling of the collected current enables to get insights into the drift and diffusion of carriers in the ensemble, key to engineer efficient charge transport. By integrating WSe
2 on in-plane 1D GaAs nanostructures, we demonstrate the lateral confinement of the electric field in regions as narrow as 250 nm in 2D-1D heterostructures. It is worthy to note that this process allows to obtain deterministatically positioned rectifying elements with sub-micron dimensions. These results prove the potential of nanoscale functional mapping for ultra-thin technologies and pave the way to engineer arrays of nano-heterojunctions.
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[6] Chowdhury, T. et al. ACS Photonics, 8 (2021)
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[8] Piazza, V. et al. Appl. Phys. Lett. 114, (2019)
[9] Dede, D. et al. Nanotechnology 33, (2022)
[10] Morgan, N. et al. Cryst. Growth Des. 23, (2023)