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Motivated by the wide-band-gap semiconductor properties of Zn-monochalcogenides (Zn-X; X:S, Se and Te), especially for their crucial industrial applications, we use a first-principles approach to investigate the B3 (zinc blende type) to B1 (rock salt type) structural transitions in this series of compounds as a function of pressure and temperature. Under static conditions (i.e., T = 0 K), the transition pressure is found to steadily drop from ZnS to ZnTe via intermediate ZnSe. Our calculations within quasi-harmonic approximation yield negative Clapeyron slopes of the B3–B1 phase boundaries for all the three compounds, where ZnTe has the highest negative slopes. We also present a completely new set of calculations for the thermoelasticity of Zn-X phases in the temperature range 0–1100 K. This article then addresses how the B3–B1 phase transitions can influence the mechanical as well as electronic properties of Zn-X. This phase transition always results in a softening of their elastic constant C12; however, C11 and C44 get stiffened. The same structural transition switches a semiconductor to conductor-type electronically favorable transition, as inferred from their high-pressure electronic structure. Among the three Zn-X compounds, ZnTe becomes the most metallic phase following the B3–B1 transition. Our findings offer a novel explanation for the complete loss of semiconductor property of these monochalcogenides at elevated pressures. [ABSTRACT FROM AUTHOR]

The electronic structures and transport properties in monolayer blue phosphorene nanoribbons (BPNRs) with transverse electric field have been studied by using density functional theory and nonequilibrium Green's functions method. The results show that the band gaps of BPNRs with both armchair and zigzag edges are linearly decreased with the increasing of the strength of transverse electric field. A semiconductor-metal transition occurs when the electric field strength reaches to 5 V/nm. The Stark coefficient presents a linear dependency on BPNRs widths, and the slopes of both zBPNRs and aBPNRs are 0.41 and 0.54, respectively, which shows a giant Stark effect occurs. Our studies show that the semiconductor-metal transition originates from the giant Stark effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • The QLs-Al 2 O 3 with different stacking modes show different electronic properties. • The variable electronic properties of QLs-Al 2 O 3 depend on the interlayer charge transfer. • The transferred electrons in QLs-Al 2 O 3 flow from higher potential to lower potential. Two-dimensional (2D) quintuple-layer (QL) Al 2 O 3 with intrinsic out-of-plane polarization exhibit many interesting physical properties. We systematically study the structural and electronic properties of QL-Al 2 O 3 layers using the first-principles calculations. Our results show that polarized QL-Al 2 O 3 is semiconductor with an indirect bandgap. For few QLs-Al 2 O 3 system, its electronic properties can be either semiconductor or metal, depending on the stacking mode of each QL-Al 2 O 3. When the stacked 2QLs-Al 2 O 3 and 3QLs-Al 2 O 3 system possess the same polarization direction, they behave the metallicity with the presence of 2D electron gas and 2D hole gas at two separate surfaces. The metallicity originates from directly interlayer band alignment and from indirectly two-step interfacial charge transfer mechanism with an enhanced surface charge. While for the stacked 2QLs-Al 2 O 3 and 3QLs-Al 2 O 3 system with opposite polarization direction, the disappeared potential difference and interfacial charge transfer make them keep the semiconductor. The revealed semiconductor-metal transition mechanism in stacked QLs-Al 2 O 3 materials is also applicable to other 2D polarized van der Waals materials and heterostructures. [ABSTRACT FROM AUTHOR]

The effect of laser and magnetic field on the semiconductor-metal transition in a Cd1-x2Mnx2Te/Cd1-x1Mnx1Te/Cd1-x2Mnx2Te quantum well has been investigated using variational principle in effective mass approximation for smaller Mn composition. The effect of non parabolicity of the conduction band has been included in our calculation. The results are presented and discussed. [ABSTRACT FROM AUTHOR]

The electronic structures and magnetic features of 3 d transition metals (TM) Cr-, Fe-, Ni-doped InN monolayers are studied by using density functional calculations. The results show that doping these transition metals into InN monolayer can generate magnetic moments, which are primarily distributed in the 3 d atoms and their neighboring N atoms. The Cr- and Fe-doped InN monolayers are magnetic semiconductors, while the Ni-doped InN monolayer shows a half-metallic characteristic. The ferromagnetic (FM) and antiferromagnetic (AFM) couplings of Cr-, Fe-, and Ni-doped InN monolayers are also investigated. It is found that the Cr-doped InN monolayer may exhibit the room-temperature ferromagnetism. Finally, under the biaxial tensile strains, for these magnetically doped InN monolayers, semiconductor-metal phenomenon can be observed. [ABSTRACT FROM AUTHOR]

Semiconductor-metal transition in BAs/BP/BAs/BP sandwiched heterostructure and BAs/BP double-walled nanotubes. • Semiconductor-metal transition occurred in the BAs/BP sandwiched heterostructures. • Semiconductor-metal transition induced by the rotation between inner and outer tubes. • Negative differential resistance in the BAs60 two-probe devices. Significant endeavors have been made to predict the van der Waals (vdW) heterostructures consisted of boron arsenide (BAs) and boron phosphide (BP) sheets, which are indispensable for next-generation nanoelectronic devices. Theoretical results show that the BP intercalation in the BAs/BP sandwiched heterostructures induce a peculiar semiconductor-metal transition, and further results in a dramatic increase in the electronic current, very different from the pure BAs and BP sheets. More strikingly, when a small BP nanotube is inserted into a larger BAs nanotube, because of the rotation between the inner and outer tubes, also leading to the similar semiconductor-metal transition. The semiconductor-metal transition in the sandwiched heterostructures composed of BAs and BP sheets gives a theoretical support for the fundamental science and device technologies and provides a possible approach to design conducting heterostructures by different monolayer semiconductors. [ABSTRACT FROM AUTHOR]

While SmS thin films show an irreversible semiconductor-metal transition upon application of pressure, the switching characteristics can be modified by alloying with other elements, such as europium. This manuscript reports on the resistance response of tri-layer SmS/EuS/SmS thin films upon applying pressure and on the correlation between the resistance response and the interdiffusion between the layers. SmS thin films were deposited by e-beam sublimation of Sm in an H2S atmosphere, while EuS was directly sublimated by e-beam from EuS. Structural properties of the separate thin films were first studied before the deposition of the final nanocomposite tri-layer system. Piezoresistance measurements demonstrated two sharp resistance drops. The first drop, at lower pressure, corresponds to the switching characteristic of SmS. The second drop, at higher pressure, is attributed to EuS, partially mixed with SmS. This behavior provides either a well-defined three or two states system, depending on the degree of mixing. Depth profiling using x-ray photoelectron spectroscopy (XPS) revealed partial diffusion between the compounds upon deposition at a substrate temperature of 400 °C. Thinner tri-layer systems were also deposited to provide more interdiffusion. A higher EuS concentration led to a continuous transition as a function of pressure. This study shows that EuS-modified SmS thin films are possible systems for piezo-electronic devices, such as memory devices, RF (radio frequency) switches and piezoresistive sensors. [ABSTRACT FROM AUTHOR]

The structural, electrical, and magnetic properties of armchair black phosphorene nanoribbons (APNRs) edge-functionalized by transitional metal (TM) elements V, Cr, and Mn were studied by the density functional theory combined with the non-equilibrium Green's function. Spin-polarized edge states introduce great varieties to the electronic structures of TM-APNRs. For APNRs with Mn-stitched edge, their band structures exhibit half-semiconductor electrical properties in the ferromagnetic state. A transverse electric field can then make the Mn-APNRs metallic by shifting the conduction bands of edge states via the Stark effect. The Mn/Cr-APNR heterojunction may be used to fabricate spin p-n diode where strong rectification acts only on one spin. [ABSTRACT FROM AUTHOR]