Dependence of negative resistance characteristics of avalanching MIM diodes on current injection mechanisms

Current-controlled negative resistance characteristics are computed for avalanche injection metal/insulator/metal diodes. Current injection is taken to occur by either Schottky thermionic emission or the Fowler-Nordheim tunneling mechanism. The results presented show that the diode negative resistance characteristics depend critically on both the magnitude and field dependance of injected currents.     

Computer simulation of the small-signal admittance and negative resistance of double avalanche region IMPATT diodes

A generalized small-signal computer simulation of double avalanche region (DAR) n ⁺-p-v-n-p ⁺ Si and InP IMPATT diodes has been carried out for different frequencies and current densities taking both drift and diffusion of charge carriers into account. The simulation results show that both symmetrically and asymmetrically doped devices based on Si and InP exhibit discrete negative conductance frequency bands separated by positive conductance frequency bands. The magnitudes of both negative conductance and negative resistance of InP devices are larger than those of Si devices in case of symmetrical and asymmetrical diodes. Further, the negative resistance profiles in the depletion layer of these diodes exhibit a single peak in the middle of the drift layer in contrast to double peaks in double drift region diodes.     

Deep level states and negative photoconductivity in n-ZnO/p-Si hetero-junction diodes

Negative photoconductivity (NPC) was observed in n-ZnO/p-Si heterojunction diode grown by ultra-high vacuum sputtering method under nitrogen ambient. Under the illumination of ultra-violet light, positive photoconductivity was observed at low bias voltages, whereas NPC was observed at high bias voltages. The defect states in the ZnO layers grown on Si were analyzed by photoluminescence and deep level transient spectroscopy measurements. Two deep levels were measured at E_c-0.51 eV and E_c-0.54 eV, which might be originated from oxygen vacancy and nitrogen atom related defects, respectively. Based on the simulation of band diagram, the defect states were located below Fermi level at zero bias voltage. However, as increasing the bias voltages, NPC was observed due to the increase of empty defect states. This analysis allowed us to consider the possibility that the NPC phenomenon in n-ZnO/p-Si heterojunction diode is originated dominantly from the defect states as a carrier recombination center in ZnO layer.     

Positive and negative differential resistance in electrical conductors

A phase transition from one conducting state to another and the appearance of positive and negative differential resistance in the current-voltage characteristic is investigated experimentally for the gap instability in nonequilibrium superconductors and the avalanche breakdown in extrinsic semiconductors. Additional observation of spatial current structures in the transition regime of both solid-state systems stimulates a simple model approach connecting these spatial patterns to the measured current-voltage characteristics. Based on the underlying experimental situations considered, our model is extended to the framework of four substantial cases.     

Possibility of negative resistance effect in zero-gap semiconductors

It is believed that for α-Sn-like zero-gap semiconductor under uniaxial tensile stress, negative differential resistance effect may be obtained. If this effect is indeed found, new possibilities for building solid state oscillators will be opened up.     

Spectral characteristics of cascade master/slave/slave injection-locking of laser diodes

We have developed the master/slave/slave laser spectrometer in the blue-wavelength region. It comprises a master/slave laser combination coupled with a second-harmonic generation (SHG) enhancement cavity and a SHG-injected blue diode laser. The total power of 30 mW was obtained and the spectral characteristics and power were measured. Excluding the power of the satellite longitudinal mode of a slave/slave laser, the total power of 422.791 nm light which can be used for the magnetooptic trap for Ca was 25.5 mW.     

Series resistance calculation for the Metal-Insulator-Semiconductor Schottky barrier diodes

An accurate way of determining the series resistance R_s of Schottky Barrier Diodes (SBDs) with and without the interfacial oxide layer using forward current-voltage (I–V) characteristics is discussed both theoretically and experimentally by taking into account the applied voltage drop across the interfacial layerV _i. For the experimental discussion, the forward biasI–V characteristics of the SBDs with and without the oxide layer fabricated by LEC (the Liquid-Encapsulated Czochralski) GaAs were performed. The SBD without the oxide layer was fabricated to confirm a novel calculation method. For the theoretical discussion, an expression ofV _i was obtained by considering effects of the layer thickness and the interface state density parameters on forward biasI–V of the SBDs. The valueR _s of the SBD with interfacial oxide layer was seen to be larger than that of the SBD without the interfacial oxide layer due to contribution of this layer to the series resistance. According to the obtained theoretical formula, the value ofV _i for the SBD with the oxide layer was calculated and it was subtracted from the applied voltage values V and then the value ofR _s was recalculated. Thus, it has been shown that this new value ofR _s is in much closer agreement with that determined for the SBD without the oxide layer as predicted. Furthermore, the curves of the interface states energy distribution of each sample are determined. It was concluded that the shape of the density distribution curve and order of magnitude of the density of the interface states in the considered energy range are in close agreement with those obtained by others for Au/n-GaAs Schottky diodes by Schottky capacitance spectroscopy.     

Current controlled negative resistance phenomenon in SbPbSe system

Thin film Al/Sb₂Pb₁Se₇/Al metal-glass-metal sandwiched structures prepared using thermal evaporation technique have been studied. The I–V measurements showed that the devices switched from high resistance OFF state to a low resistance ON state when a particular voltage appeared across it. The OFF state I–V characteristics showed non-ohmic behaviour while in the ON state the devices displayed purely linear characteristics. The switching voltage (V _th) was found to depend on film thickness and temperature of the device. A linear relation between V_th and temperature was observed.     

Large negative differential resistance in graphene nanoribbon superlattices

A graphene nanoribbon superlattice with a large negative differential resistance (NDR) is proposed. Our results show that the peak-to-valley ratio (PVR) of the graphene superlattices can reach 21 at room temperature with bias voltages between 90–220 mV, which is quite large compared with the one of traditional graphene-based devices. It is found that the NDR is strongly influenced by the thicknesses of the potential barrier. Therefore, the NDR effect can be optimized by designing a proper barrier thickness. The large NDR effect can be attributed to the splitting of the gap in transmission spectrum (segment of Wannier–Stark ladder) with larger thicknesses of barrier when the applied voltage increases.     

Thermal resistance of GaAs/AlAs superlattices used in modern light-emitting diodes

Superlattices are used in modern light-emitting diodes to modify intentionally electron, phonon and/or photon transport within their volumes, which leads to their expected performance characteristics. In particular, superlattices may have a dramatic impact on device thermal properties. Superlattice thermal resistance is anisotropic and usually distinctly higher than its values in constituent bulk materials, which results from phonon reflections and/or phonon scatterings at numerous layer interfaces. In the present paper, thermal resistance of a typical superlattice of layer thicknesses neither much higher nor much lower than the phonon free path is discussed. Besides, as an important example, thermal resistance of the typical GaAs/AlAs superlattice is determined theoretically and compared with its measured values known from literature.     

Astability and negative differential resistance of the Wigner solid

We report spontaneous narrow band oscillations in the high field Wigner solid. These oscillations are similar to the recently seen and yet unexplained oscillations in the reentrant integer quantum Hall states. The current-voltage characteristic has a region of negative differential resistance in the current biased setup and it is hysteretic in the voltage biased setup. As a consequence of the unusual breakdown, the oscillations in the Wigner solid are of the relaxation type.     

Observation of negative absolute resistance in a Josephson junction

We experimentally demonstrate the occurrence of negative absolute resistance (NAR) up to about -1 Omega in response to an externally applied dc current for a shunted Nb-Al/AlO_{x}-Nb Josephson junction, exposed to a microwave current at frequencies in the GHz range. The realization (or not) of NAR depends crucially on the amplitude of the applied microwave current. Theoretically, the system is described by means of the resistively and capacitively shunted junction model in terms of a moderately damped, classical Brownian particle dynamics in a one-dimensional potential. We find excellent agreement of the experimental results with numerical simulations of the model.     

Spectral changes in homogeneous media; a quasi-optical approach

In the past decade spectral changes depending on the spatial coherence of the source have been described by a cross-spectral density method. It is shown that for Gaussian-Schell model sources a quasi-optical approach is valid which uses Gaussian beams and ABCD matrices to describe the optical system.     

Spectral changes in inhomogeneous media; a quasi-optical approach

Spectral changes in inhomogeneous media depending on the spatial coherence of the source can be described by a quasi-optical approach. Assuming a Gaussian-Schell model source the spectral changes are described by using a Gaussian beam and ABCD matrices for the propagation in the medium.     

Spectral changes in the fluorescence of chlorophyll during photosynthesis induction

With the help of a light-emitting diode with a radiation maximum at 407 nm and an S-2000 UV-VIS spectrometer connected with a computer, the spectral changes in the fluorescence of chlorophyll from acacia leaves (Acacia sp.) preliminarily subjected to a dark adaptation are studied. It is found that, in the slow induction phase, the Kautsky effect manifests itself in the “compression” of the intensity of the chlorophyll fluorescence spectrum, with this spectrum exponentially approaching the steady-state shape with a time constant of 10–20 s. Once the steady-state fluorescence spectrum of chlorophyll was established, the amount of energy delivered to the upper singlet level is one and a half times greater than at 735 nm. The ratio between the energies spent for photochemical processes of photosynthesis and for fluorescence depends on the wavelength and the instant of time of the induction period. In the steady-state state of the chlorophyll fluorescence, the values of this ratio at 685 and 735 nm are equal to 5.9 and 3.4, respectively.     

Spectral changes in stochastic light beams propagating in turbulent ocean

The behavior of the spectral composition of a typical stochastic beam in a turbulent ocean environ is revealed. The analysis is based on the extended Huygens–Fresnel principle and the coherence theory in the space-frequency domain. The optical source is assumed to be of the Gaussian Schell-model type with a single narrow Gaussian spectral line in the visible region. Optical turbulence in the ocean is assumed to be driven by temperature and salinity fluctuations. It is found that the well-known source correlation-induced spectral shift is compensated by turbulence at sufficiently large distances.     

Study of irradiation induced changes of electrical and functional characteristics in Ge doped Si diodes

P-on-n diodes fabricated on n-type Cz Si wafers with different Ge doping concentrations were irradiated with 2 MeV electrons and 1 MeV equivalent reactor neutrons using a wide range of fluences and examined by combining current and capacitance transient techniques.