Barrier Inhomogeneities Research Articles

Numerical analysis of Gaussian potential patches model depending on the substrate doping in inhomogeneous Schottky barrier diodes over a wide temperature range

The current-voltage (I-V-T) characteristics of an inhomogeneous n-type GaAs Schottky barrier diode have been investigated by numerical analysis using the modified thermionic emission (TE) current equation by Tung in the 40–320 K range at 40 K intervals. This total current (TC) equation consists of TE current and the patch current components. The patch current dominates through the low Schottky barrier height patches at low temperatures. From the I-V-T characteristics given for three different standard deviations (σ) at each substrate doping value Nd, we have determined the temperatures at which the patch current begins to dominate. The starting temperature of the patch current has decreased as the σ and Nd values decrease. It has been seen that the temperature at which the patch current component begins to dominate is about 120, 80, and 60 K for σ4, σ3, and σ2 at Nd=1.0×1014cm−3 or Nd=1.0×1015cm−3, respectively; 160, 120, and 80 K at Nd=5.0×1015cm−3; and 200, 160, and 80 K at Nd=1.0×1016cm−3, respectively. Moreover, for the substrate with high doping, it has been observed that the I-V curve of the patch current component or the TC shifts toward higher voltages than the expected position at low temperatures. Thus, from the I-V-T characteristics, it has appeared that Tung’s pinch-off model tends to be more applicable to lightly doped semiconductors. Moreover, the TC equation should be used at high temperatures because the I-V curves at high temperatures belong to the TE component, and the patch current expression without the TE component should be especially used for fit to the experimental curves at low temperatures.

High-performance β-Ga2O3 Schottky barrier diodes with Mg current blocking layer using spin-on-glass technique

This study presents a β-Ga2O3 Schottky barrier diode (SBD) with a Mg current blocking layer (Mg-CBL) fabricated via the Mg-doped spin-on-glass (Mg-SOG) technique, affording a surface roughness damage-free thermal doping process. The proposed technique improves the breakdown voltage (BV) of the β-Ga2O3 SBD from 580 to 2200 V and marginally increases the specific on-resistance from 4.0 to 4.8 mΩ cm2, yielding a notable power figure of merit exceeding 1 GW/cm2. The Mg-CBL effectively captures the electrons and mitigates the electric field, leading to a significant increase in BV and slight decrease in the forward current loss. The temperature-dependent I–V curves reveal that the reverse saturation current decreases owing to the physical mechanism of the Mg-CBL structure. Moreover, the Gaussian distribution model is applied to correct the Schottky barrier inhomogeneity stemming from the Mg-CBL. The results illustrate the promising potential of the Mg-CBL fabricated via the Mg-SOG technique for yielding high-performance β-Ga2O3 SBDs.

Tunneling and thermionic emission as charge transport mechanisms in W-based Schottky contacts on AlGaN/GaN heterostructures

This paper investigates the forward conduction mechanism of W-based Schottky diodes on AlGaN/GaN heterostructures across a temperature range of 25–150 °C. Current-Voltage measurements carried out at different temperatures (I-V-T), allow to identify two coexisting mechanisms for charge transport. At lower bias the conduction mechanism is ruled by tunneling (TU), with a characteristic energy of E00 = 75 meV extracted from the temperature dependence of the ideality factor. At higher bias the Thermionic Emission (TE) mechanism dominates, thus revealing the presence of an inhomogeneous barrier that increases from 0.77 to 0.94 eV with increasing the measurement temperature. An ideal barrier of 1.22 eV was extrapolated for a unitary ideality factor. Structural and electrical analyses performed at nanoscale level revealed the presence of a density of defects (dislocations) in the order of 4 × 109 cm−2. Conductive Atomic Force Microscopy (C-AFM) provided local electrical information, uncovering a significant correlation between the observed electrical characteristics and the nanoscale defect distribution. This detailed insight highlights the crucial role of the electrical characteristics of defects in influencing the tunneling current component at low bias, thereby providing valuable context for understanding the electrical behavior and performance of microscopic devices.

Modelling and Analysis of Inhomogeneous Back-to-Back Schottky Junction Diode

Back-to-back Schottky diode (BBSD) is a simple device structure made from Schottky junctions that can be applied in various applications. In modelling and simulating the BBSD, the inhomogeneity of the barrier height at the Schottky interface should be considered. This paper presents device models and simulation result of an inhomogeneous BBSD. Two device models with different current spreading condition are considered. The distribution of the inhomogeneous barrier height is represented by Gaussian distribution. All the computation was done using Python programming software. When the standard deviation of the barrier height increases, the apparent barrier height that influence the electrical characteristic decreased. This is consistent with the reported experimental data. Device model that considers full current spreading showed 37.8% reduction of apparent barrier height at standard deviation of 100 meV. This is greater that the model with no current spreading. The ideality factor showed correlation with the standard deviation of barrier height, particularly when no current spreading is considered. At standard deviation of 100 meV, the ideality factor increased 2.6 %. The obtained non-unity ideality factor is associated to the significant fluctuation in the barrier height. The computed temperature-dependent current curves also showed good agreement with the reported experimental results. The device model can be a convenient tool to investigate the device operation and to validate the method used for extraction of Schottky barrier parameters.

The effect of Cu-doping to the DLC interlayer on the temperature dependent current-conduction mechanisms and barrier shape of the Schottky devices

The objective of this study is to determine the temperature and voltage-dependent current conduction mechanisms (CCMs) of the Al/Cu-doped DLC/p-Si Schottky device. It is aimed to obtain extensive and detailed data by current-voltage (I–V) measurements taken with 0.3 V voltage steps in the ±4 V voltage range, at 30 K intervals from 80 K to 410 K. Firstly, an examination of the semi-logarithmic I–V curve revealed that the low temperature (LTs, 80 K–170 K), medium temperature (MTs, 200 K–290 K) and high temperature (HTs, 320 K–410 K) regions should be examined separately. The basic parameters of the Schottky device such as the ideality factor (n), reverse saturation current (Io) and zero-biasing potential barrier height (ΦBo) were obtained separately for LTs, MTs and HTs by the Thermionic Emission (TE) theory. The results obtained show that the device deviates from ideality, especially in LTs and HTs, and the n values decrease with increasing temperature, while the ΦBo values increase. The analysis of the presence of other CTMs in the Schottky device revealed that Field Emission (FE) and Thermionic Field Emission (TFE) were effective in LTs and MTs, while FE was effective in HTs. Since it is thought that quantum mechanical CTMs cannot be the cause of such a deviation from ideality due to the interface layer thickness, the existence of Gaussian Distribution originating from lateral barrier inhomogeneity was investigated. As a result, it is concluded that the Multiple Gaussian Distribution (MGD) is dominant in the possible CTMs of the Schottky device.

Characterization of interface states and investigation of possible current conduction mechanisms in the Pt, Au, Cu/n-InP Schottky diodes

Based on the capacitance/conductance–voltage (C/G–V) and current–voltage (I–V) methods, the interface characteristics and the current conduction mechanisms of Pt/n-InP Schottky contacts were studied in detail. The interface states strongly affected the values of capacitance in the depletion region. From Terman, G–V, and forward I–V methods, the interface state density (D it) was found to range from mid-1012 to mid-1013 eV−1cm−2. The forward current characteristics was not elucidated by the thermionic emission (TE) model assisted by tunneling via the interfacial layer. Rather, the spatially distributed inhomogeneous barrier could interpret the forward current characteristics. Trap-assisted tunneling involving phosphorous vacancy (VP)-related defects was observed to be dominant in the case of the reverse current characteristics. The comparison of Pt metal contact with Cu and Au contacts revealed that Pt contact has the highest D it among three contacts.

Enhanced electrical parameters of the Au/n-Si Schottky barrier diodes with graphite/graphane oxide doped PVC interlayer

In this work, Schottky Barrier diodes (SBDs) formed on n-Si substrates were created using polyvinyl-chloride (PVC) and graphite/graphene-oxide (Gt/GO) nanoparticles (NPs) doped PVC interlayers and the conduction mechanisms of the structures were compared to the reference Au/n-Si (MS) diode. The characterization methods, including x-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM), and Energy Dispersive x-Ray (EDX), were used to analyze Gt/GO NPs and examine their structural, morphological, and analytical properties. In addition to the standard I-V method, modified Norde and Cheung methods were applied to analyze the forward bias I-V characteristics to determine the impact of pure-PVC and (PVC: Gt-GO) interlayers’ main electronic parameters on the SBDs. The surface state density (N ss ) depending on energy was also determined from the forward bias current–voltage by considering the voltage-dependent ideality coefficient, n(V), and barrier height (BH), ΦB(V). The outcomes showed that, as compared to MS structures, both the pure-PVC and (PVC: Gt-GO) interlayer leads to a decrease of n, leakage-current, N ss , an increase of rectification ratio (RR), shunt-resistance (R sh ) and zero-bias barrier-height (Φ B0 ). The differences in the electronic parameters observed between the I-V, Norde, and Cheung functions indicate that these parameters are highly reliant on the voltage and the computation method utilized. The barrier inhomogeneities at the metal/semiconductor surface also affect the current-transport or conduction mechanisms.

Electrical characteristics and trap signatures for Schottky barrier diodes on 4H-SiC, GaN-on-GaN, AlGaN/GaN epitaxial substrates

The forward and reverse current transport mechanisms, temperature dependence of Schottky barrier height (SBH) and ideality factor, barrier inhomogeneity analysis, and trap parameters for Schottky barrier diodes (SBDs) fabricated on 4H-SiC, GaN-on-GaN and AlGaN/GaN epitaxial substrates are reported. High SBH is identified for Ni/4H-SiC (1.31 eV) and Ti/4H-SiC (1.18 eV) SBDs with a low leakage current density of <10−8 A cm−2 at −200 V. Thermally stimulated capacitance detects the well-known Z1/2 electron trap at E C—0.65 eV in both 4H-SiC SBDs, while an additional deep-level trap at E C—1.13 eV is found only in Ni/4H-SiC SBDs. The vertical Ni/GaN SBD exhibits a promising SBH of 0.83 eV, and two electron traps at E C—0.18 eV and E C—0.56 eV are identified from deep-level transient Fourier spectroscopy. A peculiar two-diode model behavior is detected at metal/GaN/AlGaN/GaN interface of high-electron mobility transistor (HEMT); the first diode (SBH-1 of 1.15 eV) exists at the standard Metal/GaN Schottky junction, whereas the second diode (SBH-2 of 0.72 eV) forms due to the energy difference between the AlGaN conduction band and the heterojunction Fermi level. The compensational Fe-doping-related buffer traps at E C—0.5 eV and E C—0.6 eV are determined in the AlGaN/GaN HEMT, through the drain current transient spectroscopy experiments.

Effect of lateral inhomogeneous AlGaN barrier layer on electronic properties of GaN HEMTs

In this study, an AlGaN/GaN high electron mobility transistor with lateral inhomogeneous AlGaN barrier layer (LI-AlGaN HEMT) is proposed and studied systematically. The LI-AlGaN HEMT comprises three AlGaN regions with varying Al content, connected to the source, gate, and drain, respectively. With the increase of Al content in each region, the saturation current of the LI-AlGaN HEMT increases gradually, while the on-resistance (Ron) and breakdown voltage (BV) decrease. The threshold voltage (Vth) of the LI-AlGaN HEMT depends only on the Al content of AlGaN beneath the gate. By introducing the source field plate (FP), the calculated output current of the conventional FP-HEMT is consistent with the experimental data. After optimizing Al content, the LI-AlGaN FP-HEMT has the same Vth compared with conventional FP-HEMT. However, the saturation current is increased by approximately 20 % and the Ron is decreased by approximately 30 %. Additionally, the BV is increased to 1008 V. So the optimized lateral inhomogeneous AlGaN HEMT has better DC characteristics and is suitable for high power GaN device applications.

Electrical conduction and photodiode properties of Au/Feq3/p-Si/al hybrid heterostructure

Thin films of iron tris(8-hydroxyquinoline) (Feq3) are prepared on p-Si substrates by thermal deposition under high vacuum. The current-voltage (I–V) curves of Au/Feq3/p-Si/Al heterojunction are recorded as a function of temperature range from 303 to 383 K at 20 K interval. The device shows rectification behavior, with room temperature ideality factor (n) and barrier height (φ) values of 2.30 and 0.81 eV, respectively. The temperature dependence of φ and n is explained in terms of barrier inhomogeneity, in which the homogenous φ value is estimated as 0.97 eV. The conduction mechanisms of the diode are determined and related parameters are evaluated The series resistance of the diode is estimated as a function of temperature. Up on illuminating the diode, the reverse current of the diode increases with increasing the impinging light intensity, from which the photosensitivity and photoconduction are determined.

Analysis of barrier inhomogeneities in Ti/p–type strained Si0.95Ge0.05 Schottky diodes using reverse current-voltage characteristics

Extracting electrical parameters such as barrier height inhomogeneities (BHi) from the forward bias can be very challenging in metal/semiconductor (M/Sc) contacts characterized by low barrier height and high series resistance. In this work we demonstrate that the reverse bias characteristics can be used as an efficient alternative method to investigate the inhomogeneity of low barrier height in M/Sc contacts. In particular, the BHi in Ti/p-strained Si0.95Ge0.05 Schottky barrier diodes (SBD) has been investigated using reverse current–voltage-temperature (IR-VR-T) characteristics over the temperature range of 100–300 K. The temperature dependence of the measured barrier heights (ΦRBp) using reverse-bias is successfully explained in terms of a thermionic emission (TE) current transport associated with Gaussian distribution of the barrier height due BHi. The mean homogeneous barrier height (Ф‾RBp) and its corresponding standard deviation (σRs) were determined for different reverse voltages. A decrease in Ф‾RBp and an increase in σRs with increasing reverse bias are observed, indicating a large barrier height distribution upon high applied reverse bias. The deduced average zero-field barrier height (ФFBp≈0.59eV) from IR-VR agrees well with the corresponding value determined from the forward characteristics. Moreover, the reverse bias extracted values for Richardson constant A* based on BHi model, are found in fair agreement with the reported theoretical value of 32 A cm−2 K−2 for our p-type strained Si0.95Ge0.05 alloy. Finally, the results obtained on Pd/n-type Si0.90Ge0.10 structure shown in this work fully support the utilization of such reverse bias method.

Barrier Inhomogeneity of Pt/GaN Junctions with a Low-Temperature ALD Grown ZnO Interlayer

Semiconducting GaN can realize high performance electronic and power devices owing to its high electron mobility and thermal conductivity where good metal-semiconductor contact is prerequisite. In this work, using thermal atomic layer deposition (ALD), ZnO interlayer was grown at 80°C on GaN and the Pt/ZnO/GaN heterojunctions were electrically characterized. The analyses on the current–voltage (I–V) and capacitance (C–V) data showed that the forward I–V conduction was involved with the inhomogeneous Schottky barrier. The higher density of interface states from I–V data than that from C–V data was attributed to nonuniform distribution of interface states. In addition, high density of interface states caused localized high electric field, caused higher Poole Frenkel emission coefficients than the theoretical one.

Low-temperature electrical properties and barrier inhomogeneities in ITO/β-Ga2O3 Schottky diode

This study reports the electronic properties of the indium tin oxide (ITO)/β-Ga2O3 Schottky diode through the temperature (50–320 K)-dependent current density–voltage, capacitance–voltage, and admittance spectroscopy experiments. The room-temperature turn-on voltage of the ITO/β-Ga2O3 diode was observed to be 0.83 V, and it exhibited a slow increase with decreasing temperature. The ITO/β-Ga2O3 diode's ideality factor (n) varied from 3.92 to 1.05, and the zero-bias Schottky barrier height (φbo) varied from 0.31 to 1.28 eV. The temperature-dependent n and φbo indicate the spatial inhomogeneities of the potential barrier at the Ga2O3-ITO interface. We exploit the Gaussian distribution model to explain the Schottky barrier inhomogeneities, which could be associated with the defects observed by the admittance spectroscopy method.

Temperature dependent electron transport and interface state studies on Ni/n-Si/Al/Ag lateral Schottky junction

We investigate in this work,the electron transport characteristics across Ni/n-Si Schottky junctions from temperature dependent current–voltage (I-V-T) and capacitance–voltage (C-V-T) studies. Barrier height obtained from I–V measurements exhibited upsurge with increasing temperature, whereas, the ideality factor decreases with increasing temperature within the range of 300K–400K. To analyze electron transport mechanism, possibilities of Thermionic Field Emission and Generation-Recombination have been investigated over the temperature range, and, it has been observed that due to less characteristic energy at discussed temperature range; these effects have a minor contribution to electron transport. To account for the temperature-dependent properties and lateral barrier inhomogeneity, a double Gaussian spatial distribution of the potential barrier has been observed from conventional and modified Richardson plots. The density of Interface states at different energy levels from the conduction band has also been studied.

Investigating the effects of TiO2 nanoparticles on the barrier inhomogeneity of brilliant-blue fruit dye-base solar cell

This study aims to investigate the effects of titanium dioxide nanoparticles on the barrier inhomogeneity of a brilliant-blue dye-based solar cell. The cell has been prepared by spin-coating technique. The barrier inhomogeneity was characterized by measuring the cell's current-voltage-temperature (I-V-T) characteristics. The results show that the incorporation of TiO2 nanoparticles leads to a significant reduction in the barrier inhomogeneity of the cell, which results from the improvement of charge injection at the junction. This improvement can be attributed to the role of TiO2 nanoparticles in reducing surface defects and improving the charge injection at the interface. Also, we have investigated the change in the Richardson constant. The homogeneous Richardson constant was found to be 81.63 × 10−7 Am−2K−2 for the dye and the value was modified to 22.85 × 10−7 Am−2K−2 by incorporation of nanoparticles. This illustrates that by the doping of nanoparticles modifies barrier inhomogeneity, resulting in enhanced conductivity.

Barrier Height, Ideality Factor and Role of Inhomogeneities at the AlGaN/GaN Interface in GaN Nanowire Wrap-Gate Transistor.

It is essential to understand the barrier height, ideality factor, and role of inhomogeneities at the metal/semiconductor interfaces in nanowires for the development of next generation nanoscale devices. Here, we investigate the drain current (Ids)-gate voltage (Vgs) characteristics of GaN nanowire wrap-gate transistors (WGTs) for various gate potentials in the wide temperature range of 130-310 K. An anomalous reduction in the experimental barrier height and rise in the ideality factor with reducing the temperature have been perceived. It is noteworthy that the variations in barrier height and ideality factor are attributed to the spatial barrier inhomogeneities at the AlGaN/GaN interface in the GaN nanowire WGTs by assuming a double Gaussian distribution of barrier heights at 310-190 K (distribution 1) and 190-130 K (distribution 2). The standard deviation for distribution 2 is lower than that of distribution 1, which suggests that distribution 2 reflects more homogeneity at the AlGaN/GaN interface in the transistor's source/drain regions than distribution 1.

Investigation of the interface state characteristics of the Al/Al2O3/Ge/p-Si heterostructure over a wide frequency range by capacitance and conductance measurements

In this work, Al/Al2O3/Ge/p-Si heterostructures were fabricated by e-beam thermal evaporation. The EDX (energy dispersive X-ray spectroscopy) map visually obtained the basic distribution information in a two-dimensional graph. Three-dimensional atomic Force Microscope (AFM) analysis of the roughness of the Al/Al2O3/Ge/p-Si heterostructure shows that the Al2O3 particle has approximately 4.35 nm. Quantitative analysis via histogram plots for Al2O3 interlayer grown on p-Si shows a Gaussian-like distribution, and it has a sharp profile between 0 and 2 nm on silicon, located around 1.2 nm. The current-voltage (I–V) and capacitance-conductance-voltage (C-G/ω-V) measurements were used to investigate the electrical properties of the structure at room temperature. The I–V measurements revealed two distinct linear regions, attributed to barrier inhomogeneity and distribution of interfacial state/trap densities (Dit). For this reason, we obtained Dit distributions by considering the voltage dependence of the ideality factor n(V) in two regions. Diode parameters acquired through different methods are comparatively presented with a brief literature review. Then, the C-G/ω-V measurements were conducted across a broad frequency range (from 0.3 kHz to 3 MHz), and these measurements revealed notable alterations in the electrical parameters with regard to frequency. In order to probe interface states/traps, we employed the conductance/admittance method, which provided satisfactory information about trap lifetime, following the low-high frequency (LF-HF) and Hill-Coleman methods. The effects of these states/traps on the measurements according to voltage, frequency, and energy level (Eit-Ev) are discussed in detail.

Carrier transport across PtSe2/n-type GaN heterojunction

We fabricated PtSe2/n-type GaN heterojunction diode by transferring a large-scale grown two-dimensional (2D) PtSe2 layered film onto a 3D GaN substrate. The PtSe2 film transferred onto GaN was ∼5.84-nm thick and had 11 layers with interlayer spacing of 0.52 nm. An exploration of the temperature-dependence of the current–voltage (I–V) characteristics of the PtSe2/n-type GaN heterojunction in the range 125–400 K revealed a strong dependency of the ideality factor and barrier height on measurement temperature. This indicates a presence of low- and high-barrier-height patches resembling barrier inhomogeneities along the interface. A barrier inhomogeneity analysis with a consideration for the Gaussian barrier heights distribution demonstrated the existence of a double Gaussian barrier distribution having a mean barrier height of 0.97 and 1.41 eV in low- and high-temperature regimes, respectively. An examination of the temperature-dependency of reverse leakage current indicated the dominance of variable-range hopping conduction in lower temperature region (<225 K) and Poole–Frenkel emission mechanism in higher temperature region (>250 K). The interface state density Nss of the PtSe2/n-type GaN heterojunction determined from the capacitance method was lesser than that attained from the forward I–V characteristics that can be accredited to the inhomogeneous spreading of the Nss.

Conduction mechanism of Schottky contacts fabricated on etch pits originating from single threading dislocation in a highly Si-doped HVPE GaN substrate

This paper reports the relationship between a single dislocation structure and current leakage mechanism observed in a Pt/n+-GaN Schottky contacts with the combined use of transmission electron microscopy (TEM) and conductive atomic force microscopy (C-AFM). The contacts were fabricated on a substrate grown by hydride vapor phase epitaxy. TEM analysis clarified that large- and small-size etch pits are attributed to mixed/screw and edge dislocations, respectively. Schottky contacts formed on the surfaces of large and small etch pits (L-EPC, S-EPC), a dislocation-free flat area (FLAT), and a Schottky barrier diode with a diameter of 50 μm (SBD) were prepared and their temperature-dependent current-voltage characteristics were measured using C-AFM. Analysis of the forward bias characteristics revealed that the Schottky barrier height increased and the ideality factor approached unity with increasing temperature. Such temperature dependence of the barrier height was well explained by barrier inhomogeneity at the metal/semiconductor interface. From the analysis of the reverse bias characteristics, we found that field emission (FE) currents caused by the high donor concentration of the sample were the dominant conduction mechanism for S-EPC and FLAT. On the other hand, for L-EPC, the FE currents were overlapped by Poole-Frenkel emission (PFE) currents. For SBD, the leakage currents were successfully explained by the FE and thermionic field emission (TFE) mechanisms by assuming dislocation regions with a lowered barrier height. These findings suggest that mixed dislocations are associated with PFE and lower the Schottky barrier.

Generation of spin polarization in a multibarrier structure

The possibility to induce polarized transmission is investigated in a system of multibarrier magnetic junction. In the undeformed system, the transmission is shown to depend on the incident energy but almost independent of inhomogeneity of potential barrier. A proper selection of incident energy is found sufficient to control both direction and strength of spin polarization. When deformation of momentum wave-vector is introduced, the spin polarization does not only change its dependence on energy but also its intensity. This provides evidence that besides energy, deformation of momentum wave vector could also influence and be used to drive spin of the transmitted current; gaining further control on both direction and intensity. A short survey on the role of local magnetic splitting, ordering of local magnetic field on the spin polarization is also given.