Excess Tunneling Current Research Articles

Tunneling current via dislocations in InAs and InSb infrared photodiodes

Carrier transport mechanisms are investigated in InAs and InSb infrared photodiodes. The photodiodes were prepared by thermal diffusion of Cd and ion implantation of Be into InAs and InSb single-crystal substrates of n-type conductivity, respectively. The direct current was measured as a function of bias voltage and temperature. The excess tunneling current is observed in the investigated photodiodes at small forward bias voltages. Experimental proofs are obtained that dislocations are responsible for this current. A model for the tunneling current via dislocations is briefly discussed.

Avalanche Multiplication and Excess Noise in InAs Electron Avalanche Photodiodes at 77 K

The findings of a study of impact ionization, avalanche multiplication and excess noise in InAs avalanche photodiodes at 77 K are reported. It is shown that hole impact ionization is negligible in practical devices which continue to operate as electron avalanche photodiodes, as they do at room temperature. A new electron ionization coefficient capable of modeling multiplication at 77 K is presented and it is shown that significant multiplication can be achieved in practical devices without excessive tunneling currents. The characteristic changes observed between room temperature and 77 K are discussed. This paper helps to demonstrate the potential for practical InAs electron avalanche photodiodes, operating cooled.

Defect-related tunneling mechanism of efficiency droop in III-nitride light-emitting diodes

The quantum efficiency of GaN-based light-emitting diodes (LEDs) is investigated at temperatures 77–300 K. It is found that the efficiency droop is due to a decrease in the internal quantum efficiency (IQE) in the low-energy part of the emission spectrum. The efficiency starts to decrease at a temperature independent forward voltage of Umax≈2.9 V. At this voltage tunneling current through the LED-structure begins to dominate. It is suggested that the external quantum efficiency droop is related to reduction of the IQE due to tunneling leakage of carriers from the quantum well (QW) to defect states in barriers, and to reduction of the injection efficiency by excess tunneling current under QW through deep defect states in barriers.

Low-frequency noise and charge transport in light-emitting diodes with quantum dots

In this experimental study, we have compared low-frequency (LF) noise and transport characteristics of light-emitting diodes (LEDs) with InAs quantum dots embedded in the In0.15Ga0.85As matrix with diodes of similar epitaxial structure without dots. Quantum dot (QD) and quantum well (QW) diodes have the p-i-n structure. At cryogenic temperatures, the LEDs with quantum dots exhibit pure excess tunneling transport mechanism, which originates from the energy levels introduced by quantum dots into the band gap of the intrinsic region. In the LEDs without quantum dots, an excess tunneling current was observed for small current densities. At a higher bias, another transport mechanism dominates, whose features can be explained by the Fowler-Nordheim (FN) tunneling. The low-frequency noise associated with the excess tunneling current is of 1∕f type and its power spectral density depends on the bias as S1∝I. In the diodes without dots, the relation S1∝I2 is valid at the bias, where the current transport mechanism is of Fowler-Nordheim type. In both cases, the considered noise spectral densities do not depend on temperature. We derived the explanation of the observed noise features for the QD and the QW devices on the basis of formulas for fundamental and nonfundamental noise sources, respectively. We measured the LF noise of the light emitted by idodes at room temperature and it appeared that it is a shot noise, which is not correlated with electrical noise.

New Approach to Negative Differential Conductance with High Peak-to-Valley Ratio in Silicon

In this paper we report a new approach to realize negative differential conductance (NDC) with a high peak-to-valley (P/V) ratio in silicon metal-oxide-semiconductor field effect transistors (Si MOSFETs). A P/V ratio of as large as 10 at room temperature has been demonstrated by controlling the effective biasing to p-MOSFETs fabricated on a silicon-on-insulator (SOI) wafer. Although the band-to-band tunneling current is utilized, the excess tunneling current which has ever limited the P/V ratio in the Si Esaki diode is eliminated in the proposed method. Higher P/V ratio will enable us to incorporate NDC functionality into future Si large-scale integrated (LSI) circuits and open up new possibilities for LSI applications.

Crystalline Oxides on Silicon – Alternative Dielectrics for Advanced Transistor Technologies

ABSTRACTSince the advent of the integrated circuit in 1959 and the introduction of MOS capacitors in the early ‘60’s, electronic technology has relied on silica (SiO2) as the gate dielectric in a field effect transistor. However, silica-based transistor technology is approaching fundamental limits. Feature-size-reduction and the ever-demanding technology roadmaps have imposed scaling constraints on gate oxide thickness to the point where excessive tunneling currents make transistor design untenable; an alternative gate dielectric is needed. Crystalline oxides on silicon (COS), simply by virtue of their high dielectric constants, could fundamentally change the scaling laws for silicon-based transistor technology. More importantly, COS could provide the opportunity for an entirely new device physics based on anisotropic response of crystalline oxides grown commensurately on a semiconductor. In this paper, we report that high dielectric constant alkaline earth and perovskite oxides can be grown in perfect registry with silicon. Commensurate heteroepitaxy between the semiconductor and the oxide is established via a sequenced transition that uniquely addresses the thermodynamics of a layer-by-layer energy minimization at the interface. The perfection of the physical structure couples directly to the electrical structure, and we thus obtain the unparalleled result of an equivalent oxide thickness of less than I nm in a MOS capacitor. With this demonstration it is apparent that COS presents a functional alternative to SiO2. With COS, a transistor gate can not only exhibit a much higher dielectric response, but add entirely new capabilities such as logic-state retention with the anisotropic response of ferroelectric polarization in a ferro-gated device. COS is the basis for fundamental change in semiconductor technology.

Negative differential conductance in three-terminal silicon tunneling device

Negative differential conductance based on lateral band-to-band tunneling is demonstrated in a three-terminal silicon tunneling device. The device is fabricated with the current silicon ultra-large scale integration (Si ULSI) process, taking care of the field isolation to reduce the excess tunneling current that flows over some intermediate states. It is observed that the forward biased band-to-band tunneling current is largely controlled by the gate bias which modulates the tunneling barrier width. The three-terminal Si tunneling device is promising as the post complementary metal–oxide-semiconductor device in future Si ULSI.

Liquid phase epitaxy grown PbSnSeTe/PbSe double heterostructure diode lasers

PbSe/Pb 1− x Sn x Se 1− y Te y /PbSe double heterostructure diode lasers with lattice matched PbSnSeTe quaternary or unmatched PbSnSe ternary active layers were prepared by the transient liquid phase epitaxy growth method. This is, as far as we know, the only extensive study of liquid phase epitaxy grown PbSnSe based diode lasers. Laser emission by the various PbSnSeTe (PbSnSe) active layer compositions is between 7.4–20.2 μm (496–1350 cm −1). A maximum continuous wave (cw) operating temperature of 130 K was realized with the majority of the devices operating in cw mode above 77 K. The threshold current density of the PbSe/PbSnSeTe/PbSe devices was found to be dominated by excess tunneling currents.

Pre-Oxidation Anneal Kinetics: Interface Degradation of Thin SIO2 Films on Silicon

ABSTRACTThe high temperature anneal of hydrogen terminated silicon has been shown to etch and roughen its surface. We attempt to describe the degree of this roughness and the time scale on which it occurs using several electrical measurements: excess direct tunneling currents, dielectric breakdown and the oscillations in the Fowler-Nordheim tunneling currents. From these results we draw conclusions on the time and water content dependence of pre-oxidation annealing on the microroughness of the Si/SiO2 interface.

Effect and applications of patterned laser illumination on superconducting films

Patterned laser illumination incident upon superconducting films is shown to be capable of creating dynamic superconducting-normal ($S\ensuremath{-}N$) interfaces with almost any desired pattern. The width of such a dynamic interface for a sharp illumination edge is shown to be the effective quasiparticle diffusion length. In the limit of strong phonon trapping in the film, the effective quasiparticle diffusion length approaches the thermal healing length obtained from the heat diffusion model. However, this is not the appropriate limit in general for thin films immersed in liquid helium. The ability to create dynamic $S\ensuremath{-}N$ patterns can be used in probing spatial inhomogeneity of superconducting films and tunnel junctions. An Al-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$-Pb junction was used to demonstrate the technique. For the first time, the spatial distribution of tunneling probability was obtained through the measurements of local Josephson current. It is shown that this is a much more reliable technique than attempting to infer the tunneling probability from the excess quasiparticle tunneling current due to a local laser or electron beam excitation.

Long wavelength Pb1−xSnxTe homostructure diode lasers having a gallium-doped cladding layer

The electron concentration in Ga-doped liquid phase epitaxy (LPE) layers of Pb1−xSnxTe was studied as a function of the Ga concentration in the growth solution for various x compositions. Maximum electron concentrations of 5×1019 cm−3 and 2×1018 cm−3 were measured for x=0 and x=0.3, respectively—the highest values ever published for these LPE grown compositions. n+-p-p+ Pb1−xSnxTe homostructure diode lasers with a Ga-doped cladding layer were fabricated. The lasers showed extended wavelength ranges (11.5≤λ≤18.5 μm for x=0.24 and 8.2 μm≤λ≤11.2 μm for x=0.12), and low threshold current densities (30 A/cm at T=10 K). The threshold current density at low temperatures was found to be determined by excess tunneling currents.

Forward- and reverse-bias tunneling effects in N+P silicon solar cells

Excess currents due to field-assisted tunneling in both forward and reverse bias directions have been observed in n+-p silicon solar cells. These currents arise from the effect of conducting paths produced in the depletion layer by n+ diffusion and cell processing. Forward-bias data indicate a small potential barrier with height ∼0.04 eV at the n+ end of conducting paths. Under reverse bias, excess tunneling currents involve a potential barrier at the p end of the conducting paths, the longer paths being associated with smaller barrier heights and dominating at the lower temperatures. Low-reverse-bias data give energy levels of ∼0.11 eV for lower temperatures (253–293 K) and ∼0.35 eV for higher temperatures (293–380 K). A model is suggested to explain the results.

Tunneling studies on thin film Nb-Al alloys

Relatively high quality Josephson tunnel junctions have been fabricated using e-beam coevaporated Nb-Al thin film alloys as the base electrode. Alloys of various Al concentrations, and deposited at several substrate temperatures, have been studied. Structure analysis indicates that these alloys contain metastable disordered bcc and/or amorphous phases. Low excess tunneling currents and a small barrier dielectric constant ( \varepsilon_{r} \sim 5 ) can be achieved by oxidizing an aluminum layer which is deposited on the base electrode as the tunnel barrier.

Theory of superconductors in coherent longitudinal phonon field

The effect of injection of coherent longitudinal phonons into superconductors is investigated on the basis of the theory of nonequilibrium superconductors developed by Eliashberg. The two basic experiments about this effect, which were explained from different points of view, are explained for a unified point of view. They are (i) the change in the $I\ensuremath{-}V$ characteristics of $S\ensuremath{-}I\ensuremath{-}S$ tunnel junctions due to coherent phonon injection, i.e., phonon-induced tunneling, which was observed by Lax and Vernon, and Abeles and Goldstein, and (ii) an increase in the critical current ${I}_{c}$ in bridge and point-contact junctions, which was observed by Tredwell and Jacobsen. The phonon-induced tunneling was explained in terms of the theory by Tien and Gordon for the photon-induced tunneling. The increase in ${I}_{c}$ was attributed to an enhanced superconductivity, a theory which was first discussed by Eliashberg for superconductors in an electromagnetic field. We found that the Eliashberg effect always exists, but the phonon-induced tunneling is observed only when the space average of the phonon field, i.e., the deformation potential $\ensuremath{\phi}(\stackrel{\ensuremath{\rightarrow}}{\mathrm{r}}, t)$ is nonzero in the superconductor. The tunneling current is given by the superposition of both the effects. We have computed the excess tunneling current due to the Eliashberg effect. If we inject coherent longitudinal phonons parallel to the tunnel junction, they induce a space- and time-varying scalar (deformation) potential propagating with the phonons. We investigated whether we can extend the Josephson equation for the phase difference $\ensuremath{\varphi}$, i.e., $\ensuremath{\varphi}=\frac{2eV}{\ensuremath{\hbar}}$, to the space- and time-varying potential difference $V$ due to the phonons. We found that this type of extension is not justified, contrary to the photon-field case.

Effect of magnetic impurities on fluctuations in superconducting films aboveTc

The effect of magnetic impurities on the excess tunneling current, caused by fluctuations in a Josephson junction is calculated. The two metals on opposite sides of the junction have different transition temperatures. At temperatures immediately above the transition temperature T/subc/ of the low-T/ subc/ side, the excess current versus voltage is found to have a quasi-Lorentzian shape, exactly as in the absence of pair-breaking mechanisms. However, the pair relaxation frequency is reduced by the pair-breaking mechanism, and the coherence length is enhanced. This causes a detectable diminution in the peak voltage, which can serve as a direct measure of the pair-breaking strength. It is suggested that this effect could be used to probe the critical scattering of conduction-electron spins in the vicinity of the magnetic-ordering temperature. (AIP)

Experimental Determination of the Pair Susceptibility of a Superconductor

An excess tunneling current due to order-parameter fluctuations has been found in tin---tin oxide---lead junctions just above the transition temperature of tin. Details of the variation of the excess current with voltage, magnetic field, and temperature are in agreement with a calculation by Scalapino in which the excess-current voltage characteristic is a direct measure of the frequency--- and wave-number---dependent pair susceptibility characteristic of the superconducting transition. Estimates of the pair relaxation frequency in tin based on the data are 50% greater than theoretical predictions.

Theory of Inelastic Electron-Surface-Plasmon Interactions in Metal-Semiconductor Tunnel Junctions

The excess tunneling current due to electron-surface-plasmon interactions in semiconductor-metal tunnel junctions is calculated. The expression for the second derivative of this excess current, which corresponds to structure in $\frac{{d}^{2}I}{d{V}^{2}}$ as an increase in conductance at bias voltages near the surface plasmon energy in the semiconductor, agrees with experiment both in magnitude and line shape.

Theory of Inelastic Electron-Molecule Interactions in Tunnel Junctions

The excess tunneling current due to inelastic electron-molecule interactions near the metal-insulator interface is calculated. The expression for the second derivative of this excess current is proportional to the dipole spectral weight function of the molecule.