4 research outputs found
Wannier Koopmans Method Calculations of 2D Material Band Gaps
A major drawback
of the widely successful density functional theory
is its underestimation of the material band gap. Various methods have
been proposed to correct its band gap predictions. Wannier Koopmans
method (WKM) is recently developed for this purpose to predict the
band gap of extended 3D bulk systems. While the WKM has also been
shown to be successful for isolated molecules, it is still a question
whether it will work for 2D materials that are in between the 0D molecules
and 3D bulk systems. We apply the WKM to 16 commonly known well studied
2D materials and find that the WKM predicted band gaps are on par
with their GW calculated results
Interfacial Properties of Monolayer SnS–Metal Contacts
Two-dimensional
semiconducting SnS is expected to have great potential
for application in nanoelectronics. By using both ab initio electronic
structure calculations and more reliable quantum transport simulations,
we systematically explored the interfacial properties of monolayer
(ML) SnS in contact with a series of metals (Ag, Al, Au, Pd, Cu, and
Ni) for the first time. According to the adsorption level, three categories
are found: strong adsorption is found in ML SnS–Pd and Ni contacts;
medium adsorption is found in ML SnS–Cu contacts; and weak
adsorption is found in ML SnS–Ag, Al, and Au contacts. Because
the band structure of ML SnS is destroyed in all of the contact systems,
a vertical Schottky barrier at the ML SnS–metal interface is
absent. However, at the metalized-SnS/uncontacted-SnS interface in
a transistor configuration, a lateral Schottky contact is always formed
as a result of strong Fermi level pinning (with a pinning factor of
0.17–0.28) according to the quantum transport simulations.
This work provides guidelines to design ML SnS-based devices with
optimized electrode contact for high performance
First-Principles Study of Cu<sub>9</sub>S<sub>5</sub>: A Novel p‑Type Conductive Semiconductor
Cu<sub>9</sub>S<sub>5</sub> (digenite) is a p-type semiconductor
with excellent electrical conductivity, high mobility of copper ions,
and high work function. When used as the back electrode of CdTe solar
cells, a high power conversion efficiency (PCE) is obtained. Density
functional theory (DFT) method was used to study the structural and
electronic properties of Cu<sub>9</sub>S<sub>5</sub> in this work.
From the calculated band structures, we find that the Fermi level
of the Cu<sub>9</sub>S<sub>5</sub> slightly crosses the valence band
by about 0.08 eV below the valence band maximum (VBM), indicating
a high hole concentration and potential high electrical conductivity
as a p-type semiconductor. It is also found that the crystal structure
of Cu<sub>9</sub>S<sub>5</sub> remained stable with a few Cu atoms
diffused away, which introduces a p-type doping effect. Finally, we
give a quantitative discussion on why CdTe solar cells with Cu<sub>9</sub>S<sub>5</sub> as the back electrode shows the high PCE
Few-Layer Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O: Novel H‑Bonded 2D Material and Its Abnormal Electronic Properties
Using
first-principles calculations, we study the structural and
electronic properties of a new layered hydrogen-bonded 2D material
Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O. Interestingly,
unlike other common 2D materials, such as layered van der Waals 2D
materials, the band gap of 2D Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O-(010)-(1 × 1) is smaller than bulk Fe<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O, which does
not obey the normal quantum confinement effect and can be attributed
to the edge states and the hydrogen bonds between the layers. We also
find that the band-gap variation with the reduced layers depends on
the length of the interlayer hydrogen bond and the stronger interlayer
hydrogen bond leads to the larger band gap