P-type Schottky-barrier-free contact to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Mo</mml:mi><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math> via layer-number-assist

Bilayer and few-layer <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>Mo</a:mi><a:msub><a:mi mathvariant="normal">S</a:mi><a:mn>2</a:mn></a:msub></a:mrow></a:math> show intrinsically higher electronic quality and substantially improved device performance than monolayer, and high-quality <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>Mo</c:mi><c:msub><c:mi mathvariant="normal">S</c:mi><c:mn>2</c:mn></c:msub></c:mrow></c:math> wafers with controlled layer number have been grown. In addition, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mi>Mo</e:mi><e:msub><e:mi mathvariant="normal">S</e:mi><e:mn>2</e:mn></e:msub></e:mrow></e:math> has different polymorphs such as the semiconducting H phase and semimetallic distorted T (dT) phase, and vertically stacked dT-/H-<g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:mi>Mo</g:mi><g:msub><g:mi mathvariant="normal">S</g:mi><g:mn>2</g:mn></g:msub></g:mrow></g:math> metal-semiconductor junctions (MSJs) have been synthesized. However, the contact mechanism of dT-/H (few layer)-<i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mi>Mo</i:mi><i:msub><i:mi mathvariant="normal">S</i:mi><i:mn>2</i:mn></i:msub></i:mrow></i:math> MSJs remains to be elucidated, and <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mi>p</k:mi></k:math>-type ohmic contact to <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:mrow><l:mi>Mo</l:mi><l:msub><l:mi mathvariant="normal">S</l:mi><l:mn>2</l:mn></l:msub></l:mrow></l:math> is difficult to realize due to the high ionization energy of <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mrow><n:mi>Mo</n:mi><n:msub><n:mi mathvariant="normal">S</n:mi><n:mn>2</n:mn></n:msub></n:mrow></n:math>. In the current work, we reveal a mechanism of two-dimensional (2D) semiconductors (2DSCs) layer-number-assisted metal-semiconductor (SC) interface engineering for Schottky barrier height (SBH) reduction and <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:mi>p</p:mi></p:math>-type ohmic contact is achieved based on this mechanism; 2DSCs here mean H (few layer)-<q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mrow><q:mi>Mo</q:mi><q:msub><q:mi mathvariant="normal">S</q:mi><q:mn>2</q:mn></q:msub></q:mrow></q:math> and metal-SC interfaces are the dT-/H-<s:math xmlns:s="http://www.w3.org/1998/Math/MathML"><s:mrow><s:mi>Mo</s:mi><s:msub><s:mi mathvariant="normal">S</s:mi><s:mn>2</s:mn></s:msub></s:mrow></s:math> interfaces with increasing 2DSC layers. Specifically speaking, the mechanism is as follows: (1) two competing effects coexist, namely, the interface dipole (Δ<u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:mrow><u:mi>V</u:mi></u:mrow></u:math>) at the metal-SC interface and the quasibonding (QB) between all adjacent layers, with Δ<v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:mrow><v:mi>V</v:mi></v:mrow></v:math> (QB) increasing (decreasing) SBH; (2) the effect of QB beats Δ<w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>V</w:mi></w:mrow></w:math> and hence the overall effect is decreasing SBH at the metal-SC interface; and (3) the SBH reduction effect increases with increasing 2DSC layers. The mechanism of 2DSC layer-number-assisted metal-SC interface engineering should apply also for other 2DSCs with a suitable metal and hence our current work paves an avenue for ohmic contact to few-layer 2DSCs by the accumulated interlayer QBs that widely present in 2DSCs. Published by the American Physical Society 2024