We
have investigated the electronic structure and optical properties
of zinc molybdenum oxide (Zn2Mo3O8) by using both first-principle calculations and experiments. Optical
properties of this material is very similar to other ternary oxides
of tetravalent molybdenum (A2Mo3O8: A = Mg, Fe, Cd); therefore, this study provides meaningful insight
into optical properties and possible phtotovoltaic applicability of
these class of metal oxide cluster compounds. We use state-of-the-art
methods, based on density functional theory and the GW approximation
to the self-energy, to obtain the quasiparticle band structure and
absorption spectra of the material. Our calculations shows that Zn2Mo3O8 is a near indirect gap semiconductor
with an indirect gap of 3.14 eV. The direct gap of the material is
3.16 eV. We also calculate the optical absorption in the material.
Calculated results compare well with UV–visible spectroscopy
and spectroscopic ellipsometry measurements done on polycrystalline
thin films of Zn2Mo3O8. We show the
material has a large excitonic binding energy of 0.78 eV.
The lack of techniques for counter doping in two dimensional (2D) semiconductors has hindered the development of p/n junctions, which are the basic building blocks of electronic devices. In this work, low‐energy argon ions are used to create sulfur vacancies and are subsequently “filled” with oxygen to create p‐doped MoS2−xOx. The incorporation of oxygen into the MoS2 lattice and hence band‐structure modification reveal the nature of the p‐type doping. These changes are validated by X‐ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy, and photoluminescence measurements combined with density functional theory calculations. Electrical measurements reveal a complete flip in carrier polarity from n‐type to p‐type, which is further examined using temperature‐dependent transport measurements. The enhancement of p‐field‐effect transistor characteristics is facilitated by employing top‐gated transistors and area‐selective vacancy engineering only in the contact regions. Finally, on the same flake, an in‐plane MoS2 (n)/MoS2−xOx (p) type‐I (straddling) heterojunction with rectifying behavior and excellent broadband photoresponse is demonstrated and explained using band diagrams. The spatial/metallurgical abruptness (<100 nm) of the heterojunctions is ascertained using Raman mapping. This process of vacancy engineering, which enables air‐stable, area‐selective, controlled, CMOS‐compatible doping of 2D semiconductors is envisioned to open new vistas in the development of high‐performance electronic and optoelectronic devices.
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