Using hybrid density-functional calculations we investigate the effects of native point defects on the electrical and optical properties of In 2 O 3. We analyze formation energies, transition levels, and local lattice relaxations for all native point defects. We find that donor defects are in general more energetically favorable than acceptor defects, except near O-rich conditions, where oxygen interstitials and indium vacancies have low formation energy in n-type In 2 O 3. The oxygen vacancy is the lowest-energy donor defect with transition level (2+/+) slightly below and (+/0) slightly above the conduction-band minimum (CBM), with a predicted luminescence peak at 2.3 eV associated with the transition V 0 O → V + O. Despite being a shallow donor, the oxygen vacancy becomes electrically inactive for Fermi levels at or higher than ∼0.1 eV above the CBM. This indicates that conductivity due to oxygen vacancies will saturate at rather low carrier concentrations when compared to typical carrier concentrations required for transparent conducting oxides in many device applications.

The discovery of new and stable two-dimensional (2D) materials with exotic properties is essential for technological advancement. Inspired by the recently reported penta-PdPSe, we proposed penta-NiPS as a new member of the penta-2D materials based on first-principles calculations. The penta-NiPS monolayer is stable in two polymorphs including the α phase with an identical structure as penta-PdPSe and the newly proposed β phase with rotated sublayers. Comprehensive analyses indicated that both phases are thermodynamically, dynamically, mechanically, and thermally stable. The penta-NiPS is a soft material with 2D Young’s modulus of E a = 208 N m–1 and E b = 178 N m–1 for the α phase and E a = 184 N m–1 and E b = 140 N m–1 for the β phase. Interestingly, the α-penta-NiPS showed nearly zero Poisson’s ratios along the in-plane direction, where its dimensions would be maintained when being extended. For electronic application, we demonstrated that penta-NiPS is a wide band gap semiconductor with an indirect band gap of 2.35 eV for the α phase and 2.20 eV for the β phase.

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The theoretical discovery of new and stable 2D penta materials has stimulated the technological advancement due to the anticipated exotic properties of such structure, including the recent α phase and...