Graphene-like quaternary compound SiBCN: a new wide direct band gap semiconductor predicted by a first-principles study

Due to the lack of two-dimensional silicon-based semiconductors and the fact that most of the components and devices are generated on single-crystal silicon or silicon-based substrates in modern industry, designing two-dimensional silicon-based semiconductors is highly desired. With the combination of a swarm structure search method and density functional theory in this work, a quaternary compound SiBCN with graphene-like structure is found and displays a wide direct band gap as expected. The band gap is of ~2.63 eV which is just between ~2.20 and ~3.39 eV of the highlighted semiconductors SiC and GaN. Notably, the further calculation reveals that SiBCN possesses high carrier mobility with ~5.14x10^3 and ~13.07x10^3 cm^2V^-1s^-1 for electron and hole, respectively. Furthermore, the ab initio molecular dynamics simulations also show that the graphene-like structure of SiBCN can be well kept even at an extremely high temperature of 2000 K. The present work tells that designing ulticomponent silicides may be a practicable way to search for new silicon-based low-dimensional semiconductors which can match well with the previous Si-based substrates

Substrate-induced half-metallic property in epitaxial silicene

For most practical applications in electronic devices, two-dimensional materials should be transferred onto semiconducting or insulating substrates, since they are usually generated on metallic substrates. However, the transfer often leads to wrinkles, damages, contaminations and so on which would destroy the intrinsic properties of samples. Thus, generating two-dimensional materials directly on nonmetallic substrates has been a desirable goal for a long time. Here, via a swarm structure search method and density functional theory, we employed an insulating N-terminated cubic boron nitride(111) surface as a substrate for the generation of silicene. The result shows that the silicene behaves as a ferromagnetic half-metal because of the strong interaction between silicon and surface nitrogen atoms. The magnetic moments are mainly located on surface nitrogen sites without bonding silicon atoms and the value is about 0.12 uB. In spin-up channel, it behaves as a direct band gap semiconductor with a gap of around 1.35 eV, while it exhibits metallic characteristic in spin-down channel, and the half-metallic band gap is about 0.11 eV. Besides, both the magnetic and electronic properties are not sensitive to the external compressive strain. This work maybe open a way for the utility of silicene in spintronic field

Atomically thin mononitrides SiN and GeN: new two-dimensional semiconducting materials

Low-dimensional Si-based semiconductors are unique materials that can both match well with the Si-based electronics and satisfy the demand of miniaturization in modern industry. Owing to the lack of such materials, many researchers put their efforts into this field. In this work, employing a swarm structure search method and density functional theory, we theoretically predict two-dimensional atomically thin mononitrides SiN and GeN, both of which present semiconducting nature. Furthermore study shows that SiN and GeN behave as indirect band gap semiconductors with the gap of 1.75 and 1.20 eV, respectively. The ab initio molecular dynamics calculation tells that both two mononitrides can exist stably even at extremely high temperature of 2000 K. Notably, electron mobilities are evaluated as 0.888x$10^3$ $cm^2V^{-1}s^{-1}$ and 0.413x$10^3$ $cm^2V^{-1}s^{-1}$ for SiN and GeN, respectively. The present work expands the family of low-dimensional Si-based semiconductors.Comment: arXiv admin note: text overlap with arXiv:1703.0389

Piezoelectric MEMS Disk Resonator and Filter Based on Epitaxial Al0.3Ga0.7As Films

In this work, a new class of disk, contour-mode, piezoelectric, micromechanical resonators based on single-crystal Al0.3Ga0.7As films has been developed. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wave length of the desired resonance frequency. The resonators are designed with supports to emulate free-free boundary conditions. Finite element analysis (FEA) model for this resonator is created in Ansys software, the simulation results validate the design concept. The performance parameters extracted from the FEA models show that this novel disk resonator outperforms the beam type counterpart. A unique 7-mask MEMS fabrication process based on the epitaxial, heterostructure Al0.3Ga0.7As films has been developed and successfully implemented to produce the prototypes of the new disk resonators. Fully experimental characterizations on the prototypes were conducted and the measured results from the prototypes are: a Q factor of 7031 at 30.2 MHz with 1.11 kΩ intrinsic motional resistance; a Q factor of 6515 at 40.8 MHz with 1.26 kΩ intrinsic motional resistance; a Q factor of 3300 at 62.3 MHz with 2.43 kΩ intrinsic motional resistance. The measured power handling level is about 1.6 mW, which is the highest power handling capability to date. These measured performance aspects are better than that of the previously developed beam type resonators. Based on this new disk resonator, two novel, two-port resonators (i.e., filters) designs have been introduced. The FEA models of both designs were created and the simulation results verify these design concepts. Equivalent circuit models for these filters were established with the parameters obtained from the FEA models. Furthermore, the optimal electrode configuration to provide minimum insertion loss is obtained through the analytical transadmittance function of the equivalent circuit. The prototypes of the filters were successfully fabricated. Measured results on these prototypes are summarized here: for the circular patter design, the best insertion loss is -45.7 dB at 37.8 MHz with quality factor 4372; for the half plane electrode design, the best insertion loss is -42.8 dB at 38.1 MHz with quality factor 3632

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