Browsing by Subject "Electron tunneling"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Open Access Current-Transport mechanisms in the AlInN/AlN/GaN single-channel and AlInN/AlN/GaN/AlN/GaN double-channel heterostructures(Elsevier, 2013) Arslan, E.; Turan, S.; Gökden, S.; Teke, A.; Özbay, EkmelCurrent-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single channel (SC) and AlInN/AlN/GaN/AlN/GaN double channel (DC) heterostructures. A simple model was adapted to the current-transport mechanisms in DC heterostructure. In this model, two Schottky diodes are in series: one is a metal-semiconductor barrier layer (AIInN) Schottky diode and the other is an equivalent Schottky diode, which is due to the heterojunction between the AlN and GaN layer. Capacitance-voltage studies show the formation of a two-dimensional electron gas at the AlN/GaN interface in the SC and the first AlN/GaN interface from the substrate direction in the DC. In order to determine the current mechanisms for SC and DC heterostructures, we fit the analytical expressions given for the tunneling current to the experimental current-voltage data over a wide range of applied biases as well as at different temperatures. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. At both a low and medium forward-bias voltage values for Schottky contacts on AlInN/AlN/GaN/AlN/GaN DC and AlInN/AlN/GaN SC heterostructures, the data are consistent with electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-420 K.Item Open Access Energy-transfer rate in a double-quantum-well system due to Coulomb coupling(Elsevier, 2002) Senger, R. T.; Tanatar, BilalWe study the energy-transfer rate for electrons in a double-quantum-well structure, where the layers are coupled through screened Coulomb interactions. The energy-transfer rate between the layers (similar to the Coulomb drag effect in which the momentum-transfer rate is considered) is calculated as functions of electron densities, interlayer spacing, the temperature difference of the 2DEGs, and the electron drift velocity in the drive layer. We employ the full wave vector and frequency-dependent random-phase approximation at finite temperature to describe the effective interlayer Coulomb interaction. We find that the collective modes (plasmons) of the system play a dominant role in the energy-transfer rates.Item Open Access Forward tunneling current in Pt/p-InGaN and Pt/n-InGaN Schottky barriers in a wide temperature range(Elsevier, 2012-07-27) Arslan, E.; Çakmak, H.; Özbay, EkmelThe current-transport mechanisms of the Pt contacts on p-InGaN and n-InGaN were investigated in a wide temperature range (80-360 K) and in the forward bias regime. It was found that the ideality factor (n) values and Schottky barrier heights (SBHs), as determined by thermionic emission (TE), were a strong function of temperature and Φb0 show the unusual behavior of increasing linearly with an increase in temperature from 80 to 360 K for both Schottky contacts. The tunneling saturation ( JTU(0)) and tunneling parameters (E 0) were calculated for both Schottky contacts. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. The results indicate that the dominant mechanism of the charge transport across the Pt/p-InGaN and Pt/n-InGaN Schottky contacts are electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-360 K.Item Open Access MIMIM photodetectors using plasmonically enhanced MIM absorbers(SPIE, 2017) Dereshgi, S. Abedini; Okyay, Ali KemalWe demonstrate super absorbing metal-insulator-metal (MIM) stacks and MIMIM photosensitive devices operating at visible and near-infrared (VIS-NIR) spectrum, where absorbing (top) MIM and photocollecting (bottom) MIM can be optimized separately. We investigate different bottom metals in absorbing MIM with nanoparticles realized by dewetting of silver thin film on top. While gold and silver have conventionally been considered the most appropriate plasmonic absorbers, we demonstrate different absorbing metals like aluminum and specifically chromium, with its plasma frequency happening at 850 nm, as more efficient layers for absorption. Absorption in chromium hits 82 percent around 1000 nm. We provide convincing evidences by doing reflection experiment and computational simulations for absorbing MIM part. We also suggest for the first time investigating electric loss tangent of metal or coherently, surface plasmon quality factor of absorbing metals which are reliable tools for engineering different metal layers. They reveal that despite the fact that gold and silver are good plasmonic scatterers in VIS-NIR and reliable absorbers in VIS region, they are not proper choices as absorbers for NIR applications. Once the most optimum absorbing design is pointed out, we integrate it on top of another metal-insulator to form an MIMIM photodetector with tunneling photocurrent path. The final optimized sample consisting of silver - hafnium oxide - chromium - aluminum oxide - silver nanoparticles (from bottom to top) has a dark current of 7nA and a photoresponsivity peak of 0.962 mA/W at 1000 nm and a full width at half maximum of 300 nm, while applied bias is 50 mV and device areas are 300 μm x 600 μm. This photoresponse shows 70 times enhancement compared to former reported spin coated rare nanoparticle MIMIMs.Item Open Access A new method of probing the phonon mechanism in superconductors, including MgB2(2001) Park, M.-A.; Savran, K.; Kim, Y.-J.Weak localization has a strong influence on both the normal and superconducting properties of metals. In particular, since weak localization leads to the decoupling of electrons and phonons, the temperature dependence of resistance (i.e. λtr) decreases with increasing disorder, as manifested by Mooij's empirical rule. In addition, Testardi's universal correlation of Tc (i.e. λ) and the resistance ratio (i.e. λtr) follows. This understanding provides a new means to probe the phonon mechanism in superconductors, including MgB2. The merits of this method are its applicability to any superconductor and its reliability because the McMillan's electron-phonon coupling constant λ and λtr change in a broad range, from finite values to zero, due to weak localization. Karkin et al's preliminary data of irradiated MgB2 show the Testardi correlation, indicating that the dominant pairing mechanism in MgB2 is a phonon-mediated interaction.Item Open Access Plasma modes in layered superconductors(Elsevier B.V., 2005) Askerzade, I. N.; Tanatar, BilalAn expression for the plasmon spectrum in the layered superconductors with arbitrary thickness of planes, which varies within a wide range is obtained. The obtained result can be attractive for the explanation of experimental data on plasmon modes in cuprates and other recently discovered superconductors.Item Open Access Study of junction and bias parameters in readout of phase qubits(2012) Zandi H.; Safaei, S.; Khorasani, S.; Fardmanesh, M.The exact numerical solution of the nonlinear Ginzburg-Landau equation for Josephson junctions is obtained, from which the precise nontrivial current density and effective potential of the Josephson junctions are found. Based on the resulting potential well, the tunneling probabilities of the associated bound states are computed which are in complete agreement with the reported experimental data. The effects of junction and bias parameters such as thickness of the insulating barrier, cross sectional area, bias current, and magnetic field are fully investigated using a successive perturbation approach. We define and compute figures of merit for achieving optimal operation of phase qubits and measurements of the corresponding states. Particularly, it is found that Josephson junctions with thicker barriers yield better performance in measurements of phase qubits. The variations of characteristic parameters such as life time of the states due to the above considered parameters are also studied and discussed to obtain the appropriate configuration setup.Item Open Access Super-radiant surface emission from a quasi-cavity hot electron light emitter(Springer New York LLC, 1999) O'Brien, A.; Balkan, N.; Boland-Thoms, A.; Adams, M.; Bek, A.; Serpengüzel, A.; Aydınlı, A.; Roberts, J.The Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure (HELLISH-1) device is a novel surface emitter which utilises hot carrier transport parallel to the layers of a Ga1 - xAlxAs p-n junction incorporating a single GaAs quantum well on the n-side of the junction plane. Non-equilibrium electrons are injected into the quantum well via tunnelling from the n-layer. In order to preserve the charge neutrality in the depletion region, the junction undergoes a self-induced internal biasing. As a result the built-in potential on the p-side is reduced and hence the injection of non-equilibrium holes into the quantum well in the active region is enhanced. The work presented here shows that a distributed Bragg reflector grown below the active region of the HELLISH device increases the emitted light intensity by two orders of magnitude and reduces the emission line-width by about a factor of 3 in comparison with the original HELLISH-1 structure. Therefore, the device can be operated as an ultrabright emitter with higher spectral purity.Item Open Access Three-dimensional interaction force and tunneling current spectroscopy of point defects on rutile TiO2(110)(American Institute of Physics Inc., 2016) Baykara, M. Z.; Mönig, H.; Schwendemann, T. C.; Ünverdi, Ö.; Altman, E. I.; Schwarz, U. D.The extent to which point defects affect the local chemical reactivity and electronic properties of an oxide surface was evaluated with picometer resolution in all three spatial dimensions using simultaneous atomic force/scanning tunneling microscopy measurements performed on the (110) face of rutile TiO2. Oxygen atoms were imaged as protrusions in both data channels, corresponding to a rarely observed imaging mode for this prototypical metal oxide surface. Three-dimensional spectroscopy of interaction forces and tunneling currents was performed on individual surface and subsurface defects as a function of tip-sample distance. An interstitial defect assigned to a subsurface hydrogen atom is found to have a distinct effect on the local density of electronic states on the surface, but no detectable influence on the tip-sample interaction force. Meanwhile, spectroscopic data acquired on an oxygen vacancy highlight the role of the probe tip in chemical reactivity measurements.