The band structure of dilute-As GaNAs alloy with the As composition range from 0% to 12.5% is studied by using First-Principle density-functional calculation. Our analysis shows that the dilute-As GaNAs alloy exhibits the direct band gap properties. The dilute-As GaNAs alloy shows a band gap range from 3.645 eV down to 2.232 eV with As content varying from 0% to 12.5%, which covers the blue and green spectral regime. This finding indicates the alloy as a potential candidate for photonic devices applications. The bowing parameter of 14.5 eV 0.5 eV is also obtained using line fitting with the First-Principle and experimental data. The effective masses for electrons and holes in dilute-As GaNAs alloy, as well as the split-off energy parameters, were also presented. Minimal interband Auger recombination is also suggested for the dilute-As GaNAs alloy attributing to the off-resonance condition for this process.
A simple model is developed for studying the interaction of bright excitons in semiconducting single-wall nanotubes with charged impurities. The model reveals red shift in the energy of excitonic states in the presence of impurity, thus indicating binding of free excitons in the impurity potential well. Several bound states were found in absorption spectrum below the onset of excitonic optical transitions in the bare nanotube. Dependence of the binding energy on the model parameters, such as impurity charge and position, was determined and analytical fits were derived for a number of tubes of different diameter. The nanotube family splitting is seen in the diameter dependence, gradually decreasing with the diameter. By calculating the partial absorption coefficient for a small segment of nanotube, the local nature of the wave function of the bound states was derived.
Graphene's success for nanopore DNA sequencing has shown that it is possible to explore other potential single-and few-atom thick layers of elemental 2D materials beyond graphene (e.g., phosphorene and silicene), and also that these materials can exhibit fascinating and technologically useful properties for DNA base detection that are superior to those of graphene. Using density functional theory (DFT), we studied the interaction of DNA bases with nanopores created in finite-size nanoribbons from graphene, phosphorene, and silicene. Due to the small size of DNA bases, the bases interact with only a small section of the nanoribbon, hence using a finite-size model is appropriate for capturing the interaction of bases and 2D membrane materials. Furthermore, by using a finite-size model, our system is approximated as a molecular system, which does not require a periodic DFT calculation. We observe that binding energies of DNA bases using nanopores from phosphorene and silicene are similar, and generally smaller compared to graphene. This shows that minimal sticking of DNA bases to pore is expected for phosphorene and silicene devices. Furthermore, nanopores from phosphorene and silicene show a characteristic change in the density of states for each base. The band gaps of phosphorene and silicene are significantly altered due to interaction with DNA bases compared to graphene. Our findings show that phosphorene and silicene are promising alternatives to graphene for DNA base detection using advanced detection principles such as transverse tunneling current measurement.
A simple model which combines tight-binding (TB) approximation with parameters derived from first principle calculations is developed for studying the influence of edge passivation and uniaxial strain on electron effective mass of armchair graphene nanoribbons (AGNRs). We show that these effects can be described within the same model Hamiltonian by simply modifying the model parameters i.e., the hopping integrals and onsite energies. Our model reveals a linear dependence of effective mass on band gap for H-passivated AGNRs for small band gaps. For large band gap, the effective mass dependence on band gap is parabolic and analytic fits were derived for AGNRs belonging to different families. Both band gap and effective mass exhibit a nearly periodic zigzag variation under strain, indicating that the effective mass remains proportional to the band gap even when strain is applied. Our calculations could be used for studying carrier mobility in intrinsic AGNRs semiconductors where carrier scattering by phonons is the dominant scattering mechanism.
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