We suggest a simple approach for studying the quasi-bound fermion states induced by one-dimensional potentials in graphene. Detailed calculations have been performed for symmetric double barrier structures and n-p-n junctions. Besides the crucial role of the transverse motion of carriers, we systematically examine the influence of different structure parameters such as the barrier width in double barrier structures or the potential slope in n-p-n junctions on the energy spectrum and, especially, on the resonant-level width and, therefore, the localization of quasi-bound states.Over the last 3 years, graphene and graphene-based nanostructures have attracted much attention both experimentally and theoretically. 1,2 This is due to the fact that the lowenergy excitations in these structures are massless chiral Dirac fermions, which behave in very unusual ways when compared to ordinary electrons in the conventional twodimensional ͑2D͒ electron gas realized in semiconductor heterostructures. One of particularly interesting features of Dirac fermions is their insensitivity to external electrostatic potentials due to the so-called Klein paradox. 3 It seems that Dirac electrons can propagate to the hole states across a steep potential barrier without any damping. 4 In this situation, the confinement of electrons becomes quite a challenging task, while it is very important for producing the basic building blocks of electronic devices such as resonant structures, electron waveguides, or quantum dots ͑QDs͒. 1,2,5,6 Graphene is a single layer of carbon atoms densely packed in a honeycomb lattice, which can be treated as two interpenetrating triangular sublattices often labeled by A and B. In the presence of an external electrostatic potential V, the low-energy quasi-particles of the system are formally described by the 2D Dirac-type Hamiltonian 7,8where v F Ϸ 10 6 ms −1 is the Fermi velocity, the pseudospin matrix ជ has components given by Pauli matrices, and p ជ = ͑p x , p y ͒ is the in-plane momentum. The term mv F 2 , representing the gap in the electronic spectrum, may arise from the spin-orbit interaction, 9 from the coupling between the graphene layer and the substrate, or from the effect of covering graphene by some appropriate materials. 10,11 Eigenstates of the Hamiltonian ͑1͒ are two-component pseudospinors ⌿ = ͓ A , B ͔ T , where A and B are envelope functions associated with the probabilities at respective sublattice sites of the graphene sheet.For one-dimensional ͑1D͒ potentials V = V͑x͒ it has been shown that the finite values of the momentum parallel to potential barrier, the transverse momentum p y , can suppress the Klein tunneling, giving rise to the electron confinement. 12 This discovery opens a way of confining electrons and, particularly, making graphene-based homojunctions and even QDs using only electrostatic gates. 13,14 Moreover, in difference from conventional semiconductor QDs, to form a graphene-strip-based QD a single barrier seems to be sufficient. 13 Thus, 1D potentials can produce in graphene ...

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As requirements for infrared (IR) sensing become more stringent, demanding identification of the object rather than mere detection, imagers sensitive to a single waveband are no longer adequate in some applications. In these scenarios, the ability to "see" in multiple wavebands through a single infrared camera is indispensable. For terrestrial-based IR imaging, long-wave (LWIR) detectors are particularly suitable since the emission peaks of room temperature objects are positioned in the 8 to 12µm atmospheric window according to Planck's law. The state-of-the-art dual-band detector systems in the LWIR spectra are based on mercury cadmium telluride, though control of its spatial bandgap uniformity towards this wavelength regime can be challenging [1]. Type-II superlattices (T2SLs) enjoy a unique advantage because of the way its band-structure is determined. The electronic structure of the superlattice is controlled by the layer thicknesses, which is solely determined by the impinging rate of the group III element and does not vary much with the substrate temperature nor the flux ratios. Because of this, a wide range of cutoff wavelengths can be realized with great spatial homogeneity, which is of great benefit for imager operability and manufacturing yield, especially as imager resolutions increase.High performance dual-band T2SL imagers have only been demonstrated in the mid-wave IR [2]. Initial efforts to extend multispectral detection into longer cutoff wavelengths have been limited by the inversely decreasing energy gap that encourages coherent tunneling and surface leakage. However, in our studies on single color diodes, these issues were addressed first by blocking majority carrier tunneling across the p-n junction with a M-barrier [3] while leaving photo-generated minority carriers unhindered. The dark current characteristics improved by an order of magnitude and were observed to be limited by conductive channels along the mesa sidewalls. Subsequent modifications to the manufacturing process [4] decreased the dark current by another order of magnitude. These changes incur benefits for eventual imager performance by reducing electrical shot noise and increasing the dynamic range of the read-out integrated circuit (ROIC), which is a multiplexer with charge storage capacitors that the sensors are hybridized to for image read-out.Following these observations, we targeted for a dual-band T2SL LWIR imager [5] employing the design modifications applied to single color detectors. Unlike single color imagers, however, each spectrally sensitive layer is stacked one on top of another in an n-p-p-n fashion forming two back-to-back diodes with the shorter wavelength channel placed closer to the illumination source. The shorter "blue" channel had its 100% cutoff wavelength at 9.5µm (~130meV) while the "red" channel's cutoff was at 13µm (~95meV), approaching the VLWIR atmospheric window. Although a mere 2µm in active region thickness was grown for each channel, the quantum efficiencies (QE) were enhanced by means of Fabry-...