MS Junction Research Articles

Memristiv effect on W/Ti/p-Si structure: Aging phenomena and one of the origin of barrier inhomogeneity

Memristor as claimed to be fourth two terminal passive devices in electronics. Experimental realization memristor by HP research group is getting much more attention due to its potential applications. However, in reality this device with its unique properties always exist in MOS, MIS or even MS junctions. But its visibility has a dependence to oxide or interface thickness with mobile ions. As reported in this study, current–voltage (I-V) relation of W/Ti/p-Si continuously modified by the forward bias current. Departure form linear relation between ln(I)-V commonly analyzed with barrier inhomogeneity assumption. The appearance of barrier inhomogeneity for MS junction reported to be one of the reasons for non-ideal ln(I)-V relation. Investigation in this study shows that total charge Q(t) controlled by voltage sweep rate effecting forward ln(I)-V relation. If this situation exists, calculated barrier heights and ideality factors are not true and a pure barrier inhomogeneity approximation may not be applicable. However, under the reverse bias condition, the total charge during entire measurement is so small which it’s effect negligible over I-V relation as observed. The one of the solution is the use Missous-Rhoderick method for finding Schottky diode parameters or creating current stress over MS junction which saturates mobile ion drift. Voltage sweep rate during I-V measurement and hence total charge, affecting current transport and in parallel appearance of hysteresis loop indicate interface layer which behave as a memristor.

Investigation of conduction kinetics in Al/CuInSe2 Schottky device utilizing impedance spectroscopy (IS) measurement and study of its photosensing behaviour

Copper Indium Selenide (CuInSe2) has been synthesized by solvothermal synthesis method. The Schottky diode (SD) has been fabricated by using the material and the interface characteristics of Al/CuInSe2/ITO have been investigated with the help of ac impedance spectroscopy (IS) analysis (under dark condition) and dc current-voltage (I–V) measurements (under both dark and photo condition). IS is a very important and powerful technique to investigate and analyze the impedance at the boundary regions of SDs. Ac impedance spectra of Al/CuInSe2 SD have been recorded in the wide range of frequency from 40 Hz to 20 MHz during dc bias scanning from −0.5 V to 0.5 V under dark condition. From forward I–V characteristics, important parameters such as ideality factor (η), photosensitivity, barrier height (Φb), series resistance (RS) of SD were obtained under dark and photo condition. The photosensitivity of the Al/CuInSe2 SD was found to be 3.36. For better realization of charge transport phenomena through the MS junction, space charge limited current (SCLC) theory has been employed. The effective mobility of the carrier is evaluated in dark and photo condition as 0.42 × 10−3 m2V−1s−1 and 2.11 × 10−3 m2V−1s−1 respectively. It has been observed that the mobility is improved 5 times under illumination compared to the dark condition.

Electron – Phonon interaction to tune metal – Semiconductor junction characteristics: Ultralow potential barrier and less non-thermionic emission

We present a two-step facile method to prepare Ni2O3 coral–like and flower–like nanostructures first time followed by structural, optical characterizations by XRD, FESEM, HRTEM, Raman, luminescence spectroscopy etc. We also report rectifying I–V characteristics of Ni2O3 nanostructures/Al based metal–semiconductor junction with ultralow turn-on voltages (0.36 V), potential barrier (0.33 eV), very ideal thermionic current (η = 1.11). Photo-responsive character illustrates that the junction devices could be a promising material for light sensing application. Parameters like series resistance (111.4 Ω), electron mobility (16.73 × 10−10 m2V1s−1), diffusion length (5.13 × 10−7 m), density of states (3.09 × 1040 eVm−3) etc. have been evaluated and it is discussed that the defect (Ni3+ vacancy) induced electron–phonon interaction within the active semiconducting layer plays the crucial role to determine these parameters. Most importantly, it has been identified that the charge-transport across the junction follows non-adiabatic mechanism. Our results suggest a new insight into current transport mechanism that may be generalized to understand microstructural, defect dependence MS junctions.

Modified Interface Properties of Au/n-type GaN Schottky Junction with a High-k Ba0.6Sr0.4TiO3 Insulating Layer

The interface properties of a Au/n-GaN Schottky junction (SJ) were modified by placing a high-k barium strontium titanate (Ba0.6Sr0.4TiO3) insulating layer between the Au and n-GaN semiconductor. The surface morphology, chemical composition, and electrical properties of Au/Ba0.6Sr0.4TiO3 (BST)/n-GaN metal/insulator/semiconductor (MIS) junctions were explored by atomic force microscopy, energy-dispersive x-ray spectroscopy, current–voltage (I–V) and capacitance–voltage (C–V) techniques. The electrical results of the MIS junction are correlated with the SJ and discussed further. The MIS junction exhibited an exquisite rectifying nature compared to the SJ. An average barrier height (BH) and ideality factors were extracted to be 0.77 eV, 1.62 eV and 0.92 eV, 1.95 for the SJ and MIS junction, respectively. The barrier was raised by 150 meV for the MIS junction compared to the MS junction, implying that the BH was effectively altered by the BST insulating layer. The BH values extracted by I–V, Cheung’s and Norde functions were nearly equal to one another, indicating that the techniques applied here were dependable and suitable. The frequency-dependent properties of the SJ and MIS junction were explored and discussed. It was found that the interface state density of the MIS junction was smaller than the SJ. This implies that the BST layer plays an imperative role in the decreased NSS. Poole–Frenkel emission was the prevailed current conduction mechanism in the reverse-bias of both the SJ and MIS junction.

Surface chemical states, electrical and carrier transport properties of Au/ZrO2/n-GaN MIS junction with a high-k ZrO2 as an insulating layer

High-k zirconium oxide (ZrO2) thin insulating layer is deposited on n-type GaN and explored its chemical properties by XPS technique. XPS core level spectra confirms that the formation of ZrO2 thin film on the n-GaN substrate. Later, the Au/ZrO2/n-GaN MIS junction is constructed with a ZrO2 as insulating layer and correlated its electrical properties with the Au/n-GaN MS junction. Results present that a high barrier height (0.94 eV) is obtained for the MIS junction compared with the MS junction (0.73 eV), suggesting the barrier height is altered by the ZrO2 insulating layer. The estimated interface state density (NSS) of the MIS junction is lower compared with the MS junction, revealing that the high-k ZrO2 thin insulating layer decreased NSS. Results confirmed that the reverse leakage current mechanism is governed by a Poole-Frenkel emission in both MS and MIS junctions.

Electrical and frequency-dependent properties of Au/Sm2O3/n-GaN MIS junction with a high-k rare-earth Sm2O3 as interlayer

High-k rare-earth samarium oxide (Sm2O3) films are formed on n-GaN surface and analyzed its compositional properties by XPS measurements. XPS results specify that the Sm2O3 films are formed at the interface. Then, the Au/Sm2O3/n-GaN MIS junction is prepared with a Sm2O3 as insulating layer and correlated its electrical properties with the Au/n-GaN MS junction. The MIS junction shows highest barrier height ((0.81 eV (I-V)/1.0 eV (C-V)) for MIS junction than the MS junction (0.68 eV (I-V)/0.90 eV (C-V)). Excellent rectifying property is observed with lowest reverse leakage current and higher barrier height for the MIS junction than the MS junction, implying that the Sm2O3 insulating layer effectively modified the barrier height. The barrier heights determined from I-V, Cheung's, Norde and ΨS –V plot closely matched with each other, suggesting that these techniques are reliable and valid. The estimated interface state density of the MIS junction (1.990 × 1011 cm−2eV−1 (EC-0.82 eV)) is lower than the MS junction (9.204 × 1012 cm−2eV−1 (EC-0.70 eV)), which demonstrates that the Sm2O3 insulating layer performs an important role in lowering the interface state density. The frequency-dependent characteristics of the MS and MIS junctions are discussed in the frequency range of 10 kHz to 1 MHz and found that the determined capacitance values decrease with increasing frequency. The forward I-V characteristic of the MS and MIS junctions reveals the ohmic behavior at low voltage regions and space-charge-limited conduction at higher voltage regions. Results reveal that the reverse leakage current in the studied MS and MIS junctions is controlled by a Poole-Frenkel emission.

Common cortical responses evoked by appearance, disappearance and change of the human face

BackgroundTo segregate luminance-related, face-related and non-specific components involved in spatio-temporal dynamics of cortical activations to a face stimulus, we recorded cortical responses to face appearance (Onset), disappearance (Offset), and change (Change) using magnetoencephalography.ResultsActivity in and around the primary visual cortex (V1/V2) showed luminance-dependent behavior. Any of the three events evoked activity in the middle occipital gyrus (MOG) at 150 ms and temporo-parietal junction (TPJ) at 250 ms after the onset of each event. Onset and Change activated the fusiform gyrus (FG), while Offset did not. This FG activation showed a triphasic waveform, consistent with results of intracranial recordings in humans.ConclusionAnalysis employed in this study successfully segregated four different elements involved in the spatio-temporal dynamics of cortical activations in response to a face stimulus. The results show the responses of MOG and TPJ to be associated with non-specific processes, such as the detection of abrupt changes or exogenous attention. Activity in FG corresponds to a face-specific response recorded by intracranial studies, and that in V1/V2 is related to a change in luminance.

Polarity-dependent forming in ion bombarded amorphous silicon memory devices

Polarity-dependent forming in ion bombarded metal–semiconductor–metal (MSM) memory devices of hydrogenated amorphous silicon is reported. It is shown that prior to ion bombardment, current transport in the MSM devices is asymmetric and is controlled by the Schottky barriers at two MS junctions. Upon bombardment, however, there is a bulk component to the current and the I–V characteristics of the devices become symmetric at low bias voltages. The forming voltage in the bombarded devices shows polarity dependence. For positive bias applied on the top contact, we find that devices form at the same electric field independent of the thickness of the amorphous silicon while for negative voltage on the top contact, the electric field needed for forming increases with the thickness. A model involving the difference in energy deposition and heat sinking for the two polarities is proposed.

Rectified current in the carbon nanotube junction

A junction connecting a metallic nanotube and a semiconducting nanotube is theoretically investigated. A tight binding model is used for the analysis, which includes the Hartree–Fock approximation and the Green function method. It is found that the junction shows the opposite rectification direction compared to usual MS junctions, if the gate electrode is located nearby and the Fermi level of the semiconducting tube is near the gap.

Crossed nanotube junctions

Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e(2)/h (where e is the electron charge and h is Planck's constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction.

Spatial profiling of a luminescence impact excitation in an MS junction

A method of quasi-direct spatial profiling of a luminescence excitation in an MS junction based upon the Auger quenching of luminescence by electrons is presented. The results of experiment made on CdF 2:Mn EL MS diodes show that the regions of carrier acceleration and collision excitation are spatially separated.

The minority-carrier injection in the completely depleted MSM structure

The effect of the semiconductor parameters on the injection of carriers in a metal-semiconductor-metal structure was analyzed. It was assumed that the semiconductor is completely depleted when no external voltage is applied. We found that in that case minority carrier injection dominates over majority carrier injection. Consequently, numerical analysis shows that the current density in a metal- n-type semiconductor-metal structure increases with increasing electron barrier height and/or with decreasing donor concentration. The hole injection current dominates over the electron injection current. These relationships are opposite to those occurring both in a single MS junction and in a partly-depleted MSM junction where the minority carrier injection ratio is known to be negligibly small.

Tunneling Spectroscopy in MS and MIS Tunnel Junctions of Degenerate n-Type Semiconductor

Tunneling densities of states in degenerate n-Type Ge and n-Type Si are obtained by using Schottky barrier tunnel junctions by a method similar to that of Conley et al., but with a higher order approximation. It is shown directly by tunneling that tailings of (111) and (000) bandgaps occur in the same manner. Zero bias anomaly of V-type conductance which has often been found in tunnel junctions of III–V compounds is also observed in some MIS tunnel junctions made on degenerate n-Type Ge and n-Type Si, depending on the thickness of the insulating layer. It is difficult to explain this anomaly in terms of TA phonon excitation by tunneling electrons, as the explanation for this anomaly.

Self energy effects in tunneling in n-Ge

The self energy effect of electron—phonon deformation potential coupling in n-Ge has been observed in the tunneling in ms junctions on vacuum cleaved Ge. The effect has been measured at various impurity concentrations in the semiconductor, and it is found to disappear if the Fermi level is less than 27 mV.