Valence-Mending Passivation of Si(100) Surface: Principle, Practice and Application

2015 ◽  
Vol 242 ◽  
pp. 51-60 ◽  
Author(s):  
Meng Tao

Surface states have hindered and degraded many semiconductor devices since the Bardeen era. Surface states originate from dangling bonds on the surface. This paper discusses a generic solution to surface states, i.e. valence-mending passivation. For the Si (100) surface, a single atomic layer of valence-mending sulfur, selenium or tellurium can terminate ~99% of the dangling bonds, while group VII fluorine or chlorine can terminate the remaining 1%. Valence-mending passivation of Si (100) has been demonstrated using CVD, MBE and solution passivation. The keys to valence-mending passivation include an atomically-clean Si (100) surface for passivation and precisely one monolayer of valence-mending atoms on the surface. The passivated surface exhibits unprecedented properties. Electronically the Schottky barrier height between various metals and valence-mended Si (100) now follows more closely the Mott-Schottky theory. With metals of extreme workfunctions, new records for low and high Schottky barriers are created on Si (100). The highest barrier so far is 1.14 eV, i.e. a larger-than-bandgap barrier, and the lowest barrier is below 0.08 eV and potentially negative. Chemically silicidation between metal and valence-mended Si (100) is suppressed up to 500 °C, and the thermally-stable record Schottky barriers enable their applications in nanoelectronic, optoelectronic and photovoltaic devices. Another application is transition metal dichalcogenides. Valence-mended Si (100) is an ideal starting surface for growth of dichalcogenides, as it provides only van der Waals bonding to the dichalcogenide.

2021 ◽  
Vol 7 (13) ◽  
pp. eabd7921
Author(s):  
Yoon Seok Kim ◽  
Sojung Kang ◽  
Jae-Pil So ◽  
Jong Chan Kim ◽  
Kangwon Kim ◽  
...  

Quantum wells (QWs), enabling effective exciton confinement and strong light-matter interaction, form an essential building block for quantum optoelectronics. For two-dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic–layer–confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WOX/WSe2 hetero-bilayer formed by monolithic oxidation of the WSe2 bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, quantum-confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of band-engineered heterostructures for 2D quantum optoelectronics.


2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Yu Lan ◽  
Li-Xin Xia ◽  
Tao Huang ◽  
Weiping Xu ◽  
Gui-Fang Huang ◽  
...  

Abstract Two-dimensional (2D) transition metal dichalcogenides with intrinsically passivated surfaces are promising candidates for ultrathin optoelectronic devices that their performance is strongly affected by the contact with the metallic electrodes. Herein, first-principle calculations are used to construct and investigate the electronic and interfacial properties of 2D MoTe2 in contact with a graphene electrode by taking full advantage of them. The obtained results reveal that the electronic properties of graphene and MoTe2 layers are well preserved in heterostructures due to the weak van der Waals interlayer interaction, and the Fermi level moves toward the conduction band minimum of MoTe2 layer thus forming an n type Schottky contact at the interface. More interestingly, the Schottky barrier height and contact types in the graphene-MoTe2 heterostructure can be effectively tuned by biaxial strain and external electric field, which can transform the heterostructure from an n type Schottky contact to a p type one or to Ohmic contact. This work provides a deeper insight look for tuning the contact types and effective strategies to design high performance MoTe2-based Schottky electronic nanodevices.


2016 ◽  
Vol 04 (04) ◽  
pp. 1640010 ◽  
Author(s):  
Hongfei Liu

Atomic layer deposition (ALD) has long been developed for conformal coating thin films on planar surfaces and complex structured substrates based on its unique sequential process and self-limiting surface chemistry. In general, the coated thin films can be dielectrics, semiconductors, conductors, metals, etc., while the targeted surface can vary from those of particles, wires, to deep pores, through holes, and so on. The ALD coating technique, itself, was developed from gas-phase chemical vapor deposition, but now it has been extended even to liquid phase coating/growth. Because the thickness of ALD growth is controlled in atomic level ([Formula: see text]0.1[Formula: see text]nm), it has recently been employed for producing two-dimensional (2D) materials, typically semiconducting nanosheets of transition metal dichalcogenides (TMDCs). In this paper, we briefly introduce recent progress in ALD of multifunctional oxides and 2D TMDCs with the focus being placed on suitable ALD precursors and their ALD processes (for both binary compounds and ternary alloys), highlighting the remaining challenges and promising potentials.


2021 ◽  
Author(s):  
Chendong Zhao ◽  
Xiangli Che ◽  
Zhuang Zhang ◽  
Fu Qiang Huang

2M-WS2 as a new phase of transition metal dichalcogenides possesses many novel physical properties, such as superconductivity and topological surface states. The effect of n-type doping on the superconductivity of...


2021 ◽  
Author(s):  
Hong-Jun Zhou ◽  
Dong-Hui Xu ◽  
Qin-Hong Yang ◽  
Xiangyang Liu ◽  
Ganglong Cui ◽  
...  

Van der Waals heterojunctions formed by transition metal dichalcogenides (TMDs) and fullerenes are promising candidates for novel photovoltaic devices due to the excellent optoelectronic properties of both TMDs and fullerenes....


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