Dominant Current Transport Mechanism Research Articles

Temperature and field dependencies of current leakage mechanisms in IrOx contacts on InAlN/GaN heterostructures

This Letter reports on the mechanisms of reverse leakage current transport in InAlN/GaN heterostructure Schottky diodes with intentionally oxidized iridium oxide (IrOx) contacts across a wide temperature range. Current–voltage characteristics were experimentally measured from 25 to 500 °C (≈ 300 to 773 K). Three distinct regions in the reverse bias regime of operation and their corresponding dominant current transport mechanisms are identified. A trap-assisted tunneling mechanism is observed at low reverse bias, and trap energy levels are between 1.12 and 1.99 eV. At medium reverse bias, Poole–Frenkel emission is decomposed into low-field, mid-field, and high-field regions and the related trap activation energies vary from 0.38 to 2.04 eV. At high reverse bias, the Fowler–Nordheim model is applied and the effective barrier height to tunneling is 0.78 eV. The model of the reverse leakage current constructed using the parameters associated with these transport mechanisms closely aligns with the experimental data and supports the advancement of high-temperature electronics based on IrOx -gated InAlN/GaN heterostructure technology.

Low ohmic contact resistivity realized by in situ SiNx insertion for high Al-composition-AlGaN/GaN heterostructure

A low ohmic contact resistance (Rc) is a challenge for an AlGaN/GaN heterostructure with a high Al-composition barrier, which is highly desired to further push the performance of GaN transistors. In this Letter, an effective ohmic contact technique with an in situ SiNx layer inserted between the conventional Ti/Al/Ni/Au metal stack and the III-nitride was proposed and the inside physical mechanisms were investigated for an Al0.65Ga0.35N/GaN heterostructure. The fabricated ohmic contact has a low Rc of 0.17 Ω·mm and a specific contact resistivity value (ρc) of 8.45 × 10−7 Ω·cm2, which is obviously improved compared with the Rc of 0.32 Ω·mm and ρc of 2.84 × 10−6 Ω·cm2 without in situ SiNx inserted. The strong temperature dependency of ρc with in situ SiNx insertion shows that the dominant current transport mechanism is the thermionic field emission. Transmission electron microscopy and energy dispersive x-ray spectroscopy analyses suggest that the enhanced ohmic contact is due to the possible formation of low-work function silicides and more TiN alloys during annealing.

Unravelling the role of oxygen vacancies on the current transport mechanisms in all-perovskite nickelate/titanate heterojunctions for nonvolatile memory applications

The micrometer-sized nickelate–titanate heterojunctions with LaNiO3 (LNO) electrode have been fabricated to investigate the dominant current transport mechanisms under positive and negative bias. The LNO/SmNiO3 (SNO)/Nb:SrTiO3 (NSTO) heterojunction exhibits a highly rectifying feature with a very low leakage in a broad temperature region (from 200 to 425 K), which is attributed to the formation of a Schottky-like barrier at the SNO/NSTO interface. In addition, it is found that the trap defects (i.e., oxygen vacancies) play an essential role in determining the current density (J)–voltage (V) characteristics irrespective of the voltage polarity. The leakage current at low electric fields (<0.25 MV/cm) is dominated by temperature-enhanced trap assisted tunneling process, which is caused by the interface oxygen vacancy induced states. Further analysis suggests that, at high fields (>1.2 MV/cm), the leakage is ascribed to the bulk-limited field enhanced thermal ionization of trapped carriers in the SNO film (i.e., Poole–Frenkel emission). Specially, the oxygen vacancy redistribution near the SNO/NSTO heterointerface driven by a high temperature (425 K) or high electrical field (>3.8 MV/cm) stress is emphasized to account for the transition from the Schottky contact limited to bulk-limited conduction mechanism (i.e., space charge limited conduction). This work will benefit the further analysis of the resistive switching phenomena in nickelate-based devices, showing a potential for nonvolatile memory applications.

Analysis of Current Transport Mechanism in AP-MOVPE Grown GaAsN p-i-n Solar Cell

Basic knowledge about the factors and mechanisms affecting the performance of solar cells and their identification is essential when thinking of future improvements to the device. Within this paper, we investigated the current transport mechanism in GaAsN p-i-n solar cells grown with atmospheric pressure metal organic vapour phase epitaxy (AP-MOVPE). We examined the electro-optical and structural properties of a GaAsN solar cell epitaxial structure and correlated the results with temperature-dependent current-voltage measurements and deep level transient spectroscopy findings. The analysis of J-V-T measurements carried out in a wide temperature range allows for the determination of the dominant current transport mechanism in a GaAsN-based solar cell device and assign it a nitrogen interstitial defect, the presence of which was confirmed by DLTFS investigation.

Analysis of the current-voltage characteristic of the Schottky diode based on free-standing GaN substrate

The current–voltage (I–V) characteristics of Schottky diodes on free-standing GaN substrate are investigated by using electrical characterization and analytical modelling calculation. We have calculated the electrical parameters from experimental current-voltage curve by two methods: ln(I) and Cheung. So, we calculated different electrical parameters using experimental I-V curve such as saturation current, ideality factor, series resistance and barrier height. We have found from the first method, the ideality factor n (1.02), the barrier height fb (0.65 eV) and a series resistance Rs (84 Ω). From the second method, we have found, n (1.09), fb (0.79 eV) and Rs (79.58 Ω - 79.73 Ω). Using analytical approach, we plotted the theoretical curves for comparison with the experimental characteristic and also to determine the dominant current transport mechanism. The results found support an assumption that the dominant current mechanism in Au/n-GaN (free-standing substrate) Schottky diode is the thermionic current.

Gate Current Reduction and Improved DC/RF Characteristics in GaN-Based MOS-HEMTs Using Thermally Grown TiO2 as a Dielectric

This paper demonstrates a reduction in the gate leakage current and improvement in transistor characteristics in thermally grown TiO2/AlGaN/GaN heterostructure-based metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs). In contrast to the conventional AlGaN/GaN HEMTs, thermionic field emission through gate is not the dominant current transport mechanism for the thermally grown TiO2/AlGaN interface. The gate current is greatly affected by the properties of the oxide material and oxide–semiconductor interface in addition to the property of the barrier layer. The MOS-HEMTs with a 3.4-nm-thick TiO2 gate insulator exhibits a low gate leakage current of 10−8 Acm−2, which leads to superior device performances in terms of saturation drain current, peak transconductance, subthreshold swing, and unity gain frequency of 620 mA/mm, 158 mS/mm, 75 mV/decade, and 7 GHz, respectively, for a 400-nm gate length device. This is further augmented by an increase in ON/OFF ratio to ${5}\times {10}^{{8}}$ and a large reduction in the subthreshold leakage current by at least two orders of magnitude in comparison to that of a control HEMT. Trap-assisted tunneling (TAT) and Poole–Frenkel (PF) emission are found to be the dominant current mechanisms for gate leakage at high temperatures and moderate electric field. The activation energy of traps in PF emission is found to be 0.49 eV, and the extracted trap energy levels for the TAT are found to be in the range of 1.7–2.2 eV. The reverse bias current is found to saturate at high voltages when the field across the diode also saturates. The transistor characteristics improvement is largely ascribed to an increase in 2-D electron gas (2DEG) density.

Feasibility of 4H-SiC p-i-n Diode for Sensitive Temperature Measurements Between 20.5 K and 802 K

For the first time, we report on the performances of 4H-SiC p-i-n-diode temperature sensors for operating temperatures between 20.5 and 802 K. In this huge temperature range, three ranges of performance were identified with the limit temperatures at 78.2 and 176.3 K. In each of these ranges, a different dominant current transport mechanism is shown and in this paper, a detailed analysis and discussion are reported. The sensor performances were extracted from $V_{D} - T$ characteristics at different fixed $I_{D}$ values. In particular, at $I_{D} = 1\,\,\mu \text{A}$ and in the temperature range between 78.2 and 802 K, we found a sensor sensitivity of 2.3–3.4 mV/K with a rms temperature error, $e_{T}$ , of less than 4.2 K and the sensor shows an excellent linearity—quantified by the coefficient of determination $R^{2}$ higher than 0.9993. For even lower temperatures (below 78.2 K), low measurement currents like 10 nA are required leading to a sensitivity of 5.8 mV/K, but a lower linearity $(R^{2} = 0.9095)$ and an rms temperature error of 9.7 K which makes the sensor only partially usable in the temperature range between 20.5 and 78.2 K. Finally, the sensor performances are compared with other state-of-the-art solutions.

Temperature dependence of electrical properties in $$\hbox {In/Cu}_{{2}}\hbox {ZnSnTe}_{{4}}\hbox {/Si/Ag diodes}$$ In/Cu 2 ZnSnTe 4 /Si/Ag diodes

\(\hbox {Cu}_{{2}}\hbox {ZnSnTe}_{4}\) (CZTTe) thin films with In metal contact were deposited by thermal evaporation on monocrystalline n-type Si wafers with Ag ohmic contact to investigate the device characteristics of an In/CZTTe/Si/Ag diode. The variation in electrical characteristics of the diode was analysed by carrying out current–voltage (I–V) measurements in the temperature range of 220–360 K. The forward bias I–V behaviour was modelled according to the thermionic emission (TE) theory to obtain main diode parameters. In addition, the experimental data were detailed by taking into account the presence of an interfacial layer and possible dominant current transport mechanisms were studied under analysis of ideality factor, n. Strong effects of temperature were observed on zero-bias barrier height \((\Phi _{\mathrm{B}0} )\) and n values due to barrier height inhomogeneity at the interface. The anomaly observed in the analysis of TE was modelled by Gaussian distribution (GD) of barrier heights with 0.844 eV mean barrier height and 0.132 V standard deviation. According to the Tung’s theoretical approach, a linear correlation between \(\Phi _{\mathrm{B}0} \) and n cannot be satisfied, and thus the modified Richardson plot was used to determine Richardson constant \((A^{*})\). As a result, \(A^{*}\) was calculated approximately as \(120.6\hbox { A cm}^{-2}~\hbox {K}^{-2}\) very close to the theoretical value for n-Si. In addition, the effects of series resistance \((R_{\mathrm{s}} )\) by estimating from Cheng’s function and density of surface states \((N_{\mathrm{ss}} )\) by taking the bias dependence of effective barrier height, were discussed.

Electrical transport and capacitance characteristics of metal-insulator-metal structures using hexagonal and cubic boron nitride films as dielectrics

Metal-insulator-metal capacitor structures using thick hexagonal and cubic boron nitride (hBN and cBN) films as dielectrics are produced by plasma jet-enhanced chemical vapor deposition, and their electrical transport and capacitance characteristics are studied in a temperature range of 298 to 473 K. The resistivity of the cBN film is of the order of 107 Ω cm at 298 K, which is lower than that of the hBN film by two orders of magnitude, while it becomes the same order as the hBN film above ∼423 K. The dominant current transport mechanism at high fields (≥1 × 104 V cm−1) is described by the Frenkel-Poole emission and thermionic emission models for the hBN and cBN films, respectively. The capacitance of the hBN film remains stable for a change in alternating-current frequency and temperature, while that of the cBN film has variations of at most 18%. The dissipation factor as a measure of energy loss is satisfactorily low (≤5%) for both films. The origin of leakage current and capacitance variation is attributed to a high defect density in the film and a transition interlayer between the substrate and the film, respectively. This suggests that cBN films with higher crystallinity, stoichiometry, and phase purity are potentially applicable for dielectrics like hBN films.

Structural, electrical, and photoelectric properties of p-NiO/n-CdTe heterojunctions

p-NiO/n-CdTe-photosensitive heterojunctions were prepared by the deposition of nickel oxide thin films onto n-type single-crystal CdTe substrates by DC reactive magnetron sputtering. The analysis of capacitance-voltage (C−V) characteristics, measured at different frequencies of the small amplitude AC signal and corrected by the effect of the series resistance, provided evidence of the presence of electrically charged interface states, which significantly affect the measured capacitance. The dominant current transport mechanisms in the heterojunctions were determined at forward and reverse biases. Using “light” I−V characteristics, we determined the open-circuit voltage Voc=0.42 V, the short-circuit current Isc=57.5 μA/cm2, and the fill factor FF=0.24 under white light illumination with the intensity of 80 mW/cm2.

Current transport mechanism of Schottky contact of Pt/Au/n-InGaN

The Pt/Au Schottky contacts to InGaN samples with different background carrier concentrations are fabricated. The crystal qualities of InGaN samples are characterized by X-ray diffraction (XRD) and atomic force microscope (AFM), and the correlation between threading dislocation density of InGaN and growth temperature is further clarified. The full width at half maximum (FWHM) values of the InGaN (0002) XRD rocking curves show that the density of threading dislocations in InGaN, which can seriously deteriorate InGaN crystal quality and surface morphology, decreases rapidly with increasing growth temperature. The Hall measurements show that the background carrier concentration of InGaN increases by two orders of magnitude as growth temperature decreases from 750 to 700℃, which is due to a reduced ammonia decomposition efficiency leading to the presence of high-density donor-type nitrogen vacancy (VN) defects at lower temperature. Therefore, combining the studies of XRD, AFM and Hall, it can be concluded that the higher growth temperature is favorable for realizing the InGaN film with low density of VN defects and threading dislocations for fabricating high-quality Schottky contacts, and then the barrier characteristics and current transport mechanism of Pt/Au/n-InGaN Schottky contact are investigated by current-voltage measurements and theory analysis based on the thermionic emission (TE) model and thermionic field emission (TFE) model. The results show that Schottky characteristics for InGaN with different carrier concentrations manifest obvious differences. It is noted that the high carrier concentration leads to the Schottky barrier height and the ideality factor obtained by TE model are quite different from that by TFE model due to the presence of high density of VN defects. This discrepancy suggests that the VN defects lead to the formation of the tunneling current and further reduced Schottky barrier height. Consequently, the presence of tunneling current results in the increasing of total transport current, which means that the defects-assisted tunneling transport and TE constitute the current transport mechanism in the Schottky. However, the fitted results obtained by TE and TFE models are almost identical for the InGaN with lower carrier concentration, indicating that TE is the dominant current transport mechanism. The above studies prove that the Pt/Au/n-InGaN Schottky contact fabricated using low background carrier concentration shows better Schottky characteristics. Thus, the properly designed growth parameters can effectively suppress defects-assisted tunneling transport, which is crucial to fabricating high-quality Schottky devices.

Current transport mechanisms in Pt/Au Schottky contacts to AlInGaN using AlGaN/InGaN short-period superlattices

High-quality AlInGaN film grown by metal organic chemical vapor deposition is realized by fabricating the AlGaN/InGaN short-period superlattices, and then, Schottky contacts are fabricated on the AlInGaN superlattices. The crystal quality of AlInGaN superlattice samples is characterized by X-ray diffraction and scanning electron microscopy, and the correlation between the compositions of AlInGaN and growth condition is further clarified. The current transport mechanisms of the Pt/Au Schottky contacts to AlInGaN superlattice samples with different background carrier concentrations are studied by current–voltage (I–V) characteristics and theory analysis based on the thermionic emission (TE) and thermionic field emission (TFE) models. It is found that the results obtained from the TE and TFE models are almost identical for the Schottky contact to strain-balanced AlInGaN sample with low background carrier concentration, indicating that the thermionic emission is a dominant current transport mechanism. However, the Schottky contacts fabricated using high background carrier concentration AlInGaN samples demonstrate degraded barrier characteristics due to an occurrence of donor-like defects which result in the defect-assisted tunneling current, and thus, the combination of tunneling transport and thermionic emission constitutes the current transport mechanisms in Schottky contacts.

Silicon nanowire array architecture for heterojunction electronics

Photosensitive nanostructured heterojunctions n-TiN/p-Si were fabricated by means of titanium nitride thin films deposition (n-type conductivity) by the DC reactive magnetron sputtering onto nano structured single crystal substrates of p-type Si (100). The temperature dependencies of the height of the potential barrier and series resistance of the n-TiN/p-Si heterojunctions were investigated. The dominant current transport mechanisms through the heterojunctions under investigation were determined at forward and reverse bias. The heterojunctions under investigation generate open-circuit voltage V oc = 0.8 V, short-circuit current I sc = 3.72 mA/cm2 and fill factor FF = 0.5 under illumination of 100 mW/cm2.

Electrical characteristics of Au/n-Si (MS) Schottky Diodes (SDs) with and without different rates (graphene + Ca1.9Pr0.1Co4Ox-doped poly(vinyl alcohol)) interfacial layer

In order to see effects of interfacial (with and without different graphene (GP) + Ca1.9Pr0.1Co4Ox-doped PVA) layer on the electrical characteristics of conventional Au/n-Si (MS) contacts. Therefore, Au/(GP + Ca1.9Pr0.1Co4Ox-doped PVA)/n-Si (MPS) structures were fabricated with different rates of (%3 GP, %7 GP) PVA and were fabricated on same n-Si wafer. Au/n-Si (MS), Au/PVA/n-Si, Au/%3GP + Ca1.9Pr0.1Co4Ox-doped PVA/n-Si and Au/%7GP + Ca1.9Pr0.1Co4Ox-doped PVA/n-Si structures were fabricated and their main electrical characteristics compared each other by using current–voltage (I–V) methods. The forward and reverse bias current voltage (I–V) characteristics of with and without GP + Ca1.9Pr0.1Co4Ox-doped PVA/n-Si at room temperature were studied to investigate its main electrical parameters. The energy density distribution profile of the interface states (Nss) was obtained from the forward bias I–V data by taking into account voltage dependent ideality factor (n(v)) and effective barrier height (Φe) and they increase from at about mid-gap energy of Si to bottom of conductance band edge. In addition, voltage dependent profile of resistivity of the structure was obtained from I–V data for four different structures. The analysis of experimental results reveals that the existence of GP + Ca1.9Pr0.1Co4Ox-doped PVA interfacial layer improves the performance of MS structure. In order to determine the dominant current-transport mechanism (CTM) in the whole forward bias region of these structures, the double logarithmic forward bias I–V plots were also drawn. These plots exhibit two distinct linear region with different slopes which are corresponding to intermediate and high forward bias voltages. The slope of these plots show that in the region 1 (low biases) the dominant CTM is trap-charge-limited current (TCLC), whereas in the region 2 (high biases) is space-charge-limited current (SCLC) for four diodes.

Silicon nanowire array architecture for heterojunction electronics

Photosensitive nanostructured heterojunctions n-TiN/p-Si were fabricated by means of titanium nitride thin films deposition (n-type conductivity) by the DC reactive magnetron sputtering onto nanostructured single crystal substrates of p-type Si (100). The temperature dependencies of the height of the potential barrier and series resistance of the n-TiN/p-Si heterojunctions were investigated. The dominant current transport mechanisms through the heterojunctions under investigation were determined at forward and reverse bias. The heterojunctions under investigation generate open-circuit voltage Voc=0.8 V, short-circuit current Isc=3.72 mA/cm2 and fill factor FF=0.5 under illumination of 100 mW/сm2. DOI: 10.21883/FTP.2017.04.44354.8407

Understanding current transport at the Ni/GaN interface using low-frequency noise spectroscopy

The non-ideal behaviour of the GaN-based Schottky diode is in general attributed to the combined effect of interface traps and barrier inhomogeneities at the metal/GaN interface. In our present work, we determine the relative contribution of these two non-idealities to electronic transport in Schottky barrier diodes, by using bias-dependent low-frequency noise measurements. Due to the single-trap-dominated electronic transport at lower bias, the noise spectra turn out to be Lorentzian, whereas the distribution in time constants available for interface states due to barrier inhomogeneities causes a deviation from Lorentzian towards a 1/f-type noise spectrum in higher bias regions. The present study indicates that the shape of the noise spectrum, its level and variation with the applied bias, determine the dominant current transport mechanism at the Ni/GaN interface, which may be useful for improving the electrical behaviour of metal/GaN interfaces.

Electrical and Photoelectric Properties of the TiN/p-InSe Heterojunction

The conditions for fabricating photosensitive TiN/p-InSe heterojunctions by the reactive-magnetron sputtering of thin titanium-nitride films onto freshly cleaved p-InSe single-crystal substrates is investigated. The presence of a tunnel-transparent high-resistivity In2Se3 layer at the heterojunction is revealed from analysis of the I–V characteristics, and the effect of this layer on the electrical properties and photosensitivity spectra of the heterostructures is analyzed. The dominant current transport mechanisms through the TiN/p-InSe energy barrier under forward and reverse bias are determined.

Temperature dependent 1/f noise characteristics of the Fe/GaN ferromagnetic Schottky barrier diode

The temperature dependent current–voltage (I–V) and 1/f noise characteristics of the Fe/GaN ferromagnetic metal–semiconductor (FM/SC) Schottky barrier diode are presented. At 300 K, an ideality factor of 1.3 and a barrier height of 0.92 eV suggested thermionic emission as the dominant current transport mechanism at the FM/SC interface. The ideality factor increased to 3.4 while the barrier height decreased to 0.36 eV at 100 K, indicating the presence of other current transport mechanisms in addition to thermionic emission. The spectral power density of current fluctuations, is measured as a function of frequency in the temperature range 100–300 K, where followed with γ close to unity. A 1/f type of noise spectrum at each temperature in the range 100–300 K is attributed to the existence of barrier inhomogeneities at the Fe/GaN interface. The inhomogeneous nature of Fe/GaN is also revealed from the temperature dependent I–V characteristics. From temperature dependent I–V and 1/f noise measurements, it is found that current transport is limited by diffusion currents below 200 K, resulting in an increase in noise with temperature. Above 200 K, thermionic emission is the dominant current transport mechanism and noise behavior is affected by barrier inhomogeneities, resulting in a decrease in noise with an increase in temperature.

Current transport mechanism of AlGaN/GaN Schottky barrier diode with fully recessed Schottky anode

Both the forward and reverse-bias current transport mechanisms of an AlGaN/GaN Schottky barrier diode with a fully recessed Schottky anode (recessed-SBD) are investigated for the first time. A two-dimensional (2D) device simulation gives insight into the electronic transport. The difference between the forward and reverse conduction paths enables the reduction in Von without sacrificing the low reverse leakage current properties. The results of temperature-dependent current–voltage (T–I–V) measurements show that thermionic field emission (TFE) is the dominant current transport mechanism for forward bias. In the reverse-bias region above the pinch-off voltage, two mechanisms codetermine leakage currents, which contain Frenkel–Poole emission from the overlapped planar contact and tunneling from the recessed sidewall contact. Below the pinch-off voltage, the leakage currents are observed to have exponential temperature dependence, which may be consistent with trap-assisted tunneling (TAT).

Influence of temperature on tunneling-enhanced recombination in Si based p—i—n photodiodes

We investigate the dominant dark current transport mechanism in Si based p—i—n photodiodes, namely, BPW 21R, SFH 205FA and BPX 61 photodiodes in the temperature range of 350 to 139 K. The forward current—voltage characteristics of these photodiodes are explained via the tunneling enhanced recombination model, which gives a quantitative description of the electronic mechanism in the p—i—n junction photodiodes. The observed temperature dependence of the saturation current and the diode ideality factor of these devices agree well with theoretical predictions; the analysis also indicates the importance of doping for enhancement of tunneling. The present study will be helpful in applying the devices at low temperature ambience.