We study the processes of the electron and hole injection (double injection) into the i-region of graphene-layer and multiple graphene-layer p-i-n structures at the forward bias voltages. The hydrodynamic equations governing the electron and hole transport in graphene coupled with the two-dimensional Poisson equation are employed. Using analytical and numerical solutions of the equations of the model, we calculate the band edge profile, the spatial distributions of the quasi-Fermi energies, carrier density and velocity, and the current-voltage characteristics. In particular, we demonstrated that the electron and hole collisions can strongly affect these distributions. The obtained results can be used for the realization and optimization of graphene-based injection terahertz and infrared lasers.Comment: 10 pages, 11 figure

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We have performed an eight-band k · p model calculation on the current-voltage ͑I-V͒ curves associated with interband magnetotransport in a double-barrier broken-gap heterostructure using the Burt-Foreman multiband envelope function theory and the scattering matrix approach. In a sample with very thin barriers, the broadening ⌫ 0 of a virtual bound state with energy E 0 can be very large. Depending on the relative values of ⌫ 0 and ͉E 0 − E F ͉, where E F is the Fermi energy, the behavior of the I-V curve can be either of Ohmic type or of resonant-tunneling type, and can be tuned from one to the other by changing the applied magnetic-field strength.

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Using the Burt-Foreman envelope function theory and an eight-band k · p model, we have extended our previous work ͓Semenikhin et al. Phys. Rev. B 76, 035335 ͑2007͔͒ on optical transitions in InAs/ GaSb quantum wells grown along the ͓001͔ direction by completing the interface Hamiltonian with the inclusion of its nonrelativistic part. We found a substantial contribution of the nonrelativistic term to the originally forbidden spin-flip optical transitions. However, this nonrelativistic term produces only a minor modification of the lateral optical anisotropy.

We report on the proposal and the theoretical and experimental studies of the terahertz hot-electron bolometer (THz HEB) based on a gated GaAs structure like the field-effect transistor with the array of parallel Sn nanothreads (Sn-NTs). The operation of the HEB is associated with an increase in the density of the delocalized electrons due to their heating by the incoming THz radiation. The quantum and the classical device models were developed, the quantum one was based on the self-consistent solution of the Poisson and Schrödinger equations, the classical model involved the Poisson equation and density of states omitting quantization. We calculated the electron energy distributions in the channels formed around the Sn-NTs for different gate voltages and found the fraction of the delocalized electrons propagating across the energy barriers between the NTs. Since the fraction of the delocalized electrons strongly depends on the average electron energy (effective temperature), the proposed THz HEB can exhibit an elevated responsivity compared with the HEBs based on more standard heterostructures. Due to a substantial anisotropy of the device structure, the THz HEB may demonstrate a noticeable polarization selectivity of the response to the in-plane polarized THz radiation. The features of the THz HEB might be useful in their practical applications in biology, medicine and material science.

In this work, a new implementation of the finite-difference (FD) modal method (FDMM) based on an iterative approach to calculate the eigenvalues and corresponding eigenfunctions of the Helmholtz equation is presented. Two relevant enhancements that significantly increase the speed and accuracy of the method are introduced. First of all, the solution of the complete eigenvalue problem is avoided in favor of finding only the meaningful part of eigenmodes by using iterative methods. Second, a multigrid algorithm and Richardson extrapolation are implemented. Simultaneous use of these techniques leads to an enhancement in terms of accuracy, which allows a simple method such as the FDMM with a typical three-point difference scheme to be significantly competitive with an analytical modal method.

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