Thermionic Emission Mechanism Research Articles

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.

Influence of 700 keV O3+ ion implantation on current transport properties of Cr/p-GaN SBD’s

In the present study we show a detailed investigation into the influence of 700 keV O3+ ion implantation in Cr/p-GaN SBDs on electrical characteristics / current transport properties. Also the damage events along the trajectory of the ion beam were quantitatively estimated through SRIM and TRIM simulations. The Current-voltage (I-V) characteristics were analyzed using different methods such as Cheung and Cheung's method and Norde’s method to obtain different electrical parameters. The values of n and ϕB decrease up to a fluence of 1 × 1014 ions cm−2, and show a fractional increase at a fluence of 1 × 1015 ions cm−2. Further, a drastic increase in values of series resistance (RS ) of SBDs with an increase in fluence was observed. In the forward-bias voltage regions, the Cr/p-GaN SBDs conduction mechanism shows an increasingly ohmic behavior with an increase in fluence, which may be attributed to thermally generated carriers. At low voltage, the reverse current conduction mechanism is due to Poole-Frenkel emission. For the high voltage region, Schottky emission mechanism becomes more prominent. The changes in electrical parameters are closely related to the defect and damage profiles estimated through SRIM/TRIM simulations, which are strongly dependent on the dose of the 700 keV O3+ ion implantation. Additionally, we found that at high doses, the charge transport mechanism changes, with additional defects affecting not only the thermionic emission mechanism but also various current transport mechanisms.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

High-performance and low-power consumption deep UV photodetectors based on MOCVD-grown ZnGa2O4epilayers with high temperature functionality

This work reports on the fabrication of excellent quality deep ultraviolet photodetectors (DUV PDs) based on metalorganic chemical vapor deposition (MOCVD) grown spinel ZnGa2O4 thin films on c-plane sapphire. Herein, The DUV PDs by exhibiting an ultra-low dark current of 6.69 fA and a high photo-to-dark-current ratio (PDCR) of >108 at a low-power operation of 0.2 V. While PDCR reached more than 109 on applied bias of 10 V having extremely low dark current of 37 fA. The detector revealed an ultra-high responsivity of 185 and 3.53 A/W under the exposure of 107 μW/cm2 of 245 nm wavelength at room temperature (RT) and applied bias of 10 and 0.2 V, respectively, and exhibited the record-high detectivity of the order of 1017 Jones. The temperature-dependent operation remained stable across a wide temperature range, from 27 °C to 125 °C, maintaining ultra-low dark current. The nearly constant growth and decay time of DUV PDs throughout the temperature range emphasizes the robustness and reliability of PD. The ideality factor in both DUV and dark conditions nearing unity proves the dominance of the thermionic emission mechanism. Also shows the stable and slight improved performance after a year. Therefore, these findings suggest that ZnGa2O4 is a strong contender for deep UV detection that shows robustness even at high temperatures.

Multi-Gaussian distribution of barrier height in diamond-like carbon interfacial-layered Schottky devices

Pieces of information about the physical and electronic properties of diamond-like carbon (DLC) interfacial-layered Schottky devices are crucial because DLC is known for its durability against harsh conditions such as high voltage, high temperature, and radiative environments. Therefore, this study focused on determining some critical properties of DCL interlayered Schottky devices, such as current-conduction mechanisms (CCMs) and the shape of the barrier height of the device. Some graphics, such as n-ΦB0vs T, ΦB0vs n, ΦB0vs q/2kT, 1/n−1vs q/2kT, and ln(I0/T2-(qσs)/2k2T2vs kT/q were obtained from the temperature-dependent current-voltage (I–V-T) data to determine the shape of the barrier height (BH) and to understand CCMs of this MIS-type device. Obtained results revealed that the device exhibited different behaviours in three different temperature regions: 80–170 K, 200–290 K and 320–410 K, which were called Low Temperatures (LTs), Moderate Temperatures (MTs) and High Temperatures (HTs), respectively. It was also observed that all these graphs exhibited linear behaviour separately for these three temperature regions. Therefore, these results showed that the barrier shape of this DLC interlayered Schottky device is not homogeneous, and it has a Multi-Gaussian distribution due to three different linear behaviours. On the other hand, in addition to the Thermionic Emission (TE) mechanism, it was also understood that Field Emission (FE) and Thermionic Field Emission (TFE) mechanisms, known as Quantum Mechanical Tunnelling (QMT) mechanisms, were effective current conduction mechanisms, especially at low and moderate temperatures for this device.

Theoretical exploration of photoemission characteristics of GaAs nanowire array cathode based on photon-enhanced thermionic emission

The theoretical photoemission models of single GaAs nanowire and nanowire array cathode based on photon-enhanced thermionic emission (PETE) mechanism are respectively developed by utilizing two-dimensional continuity equations. Based on the built models in this work, the effect of several key factors on the quantum efficiency are also discussed. Results show that GaAs nanowire cathode exhibits the superiority of photoemission performance compared with GaAs film cathode at the spectral range of 300∼600 nm. Besides, the optimal wire diameter of GaAs nanowire cathode is in the range of 340∼360 nm. In addition, the nanowire cathode with low electron affinity of 0.3 eV achieves PETE effect under low temperature of 400 K, which is conducive to improve the stability of cathode. Moreover, increasing the incident light angle or decreasing the array spacing provides an effective method of obtaining high quantum efficiency of nanowire array cathode. Furthermore, the numerical difference between quantum efficiency and effective quantum efficiency implies that the low collection efficiency of emitted electrons is the main issue that hinders the application of PETE cathodes of GaAs nanowire array. The proposed GaAs nanowire array model would provide theoretical guidance for optimum design of PETE cathodes with nanoarray structure.

Thermal dependence on electrical characteristics of Au/(PVC:Sm2O3)/n-Si structure

In this study, we investigated the current–voltage (I–V) characteristics of Au/n-Si structure with an interfacial layer of Samarium Oxide (Sm2O3) nanoparticles (NPs) in polyvinyl chloride (PVC) matrix within a temperature range of 80–320 K. Applying the thermionic emission (TE) theory, essential electrical parameters such as reverse saturation current (I0), ideality factor (n), zero bias barrier height (ΦB0), series resistance (Rs), and rectification rate (RR) were carefully derived from the I–V data. The mean values of BH and Richardson constant obtained from the modified Richardson plot were determined to be 0.730 eV and 111.4 A/(cmK)2, respectively. Remarkably, this A* value closely matches its theoretical counterpart for n-type Si. Thus, our findings successfully highlight the effectiveness of the thermionic emission (TE) mechanism with the Gaussian distribution of BHs in explaining the I-V-T characteristics of the fabricated Schottky structure, shedding light on the intricate interplay between temperature and diode behavior. These insights offer valuable guidance for designing and optimizing thermal-sensitive devices based on this innovative structure.

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.

Spectroscopic analysis and device application of molecular organic dye layer in the Al/p-Si MIS contacts

In this paper, the effect of 1-phenylazo-2-naphthol (1PA2N) dye molecules used as an organic interfacial layer on the electronic features of Al/p-Si contact was investigated. An Al/1PA2N/p-Si junction was fabricated using the spin coating method. The 1PA2N dye molecule was investigated using nuclear magnetic resonance, Fourier transform infrared, ultraviolet–visible (UV–vis) spectroscopy, and atomic force microscopy (AFM) analyses. The 1PA2N dye in methanol had optical direct band energy values of 2.33 eV (Q band) and 3.70 eV (B band) according to UV–vis absorption measurements. Surface analysis using AFM indicated that the 1PA2N film on the substrate was covered in nanoparticles. Also, several junction parameters of the Al/1PA2N/p-Si structure were determined utilizing current–voltage measurements based on the thermionic emission mechanism. Moreover, the interfacial state density for the Al/1PA2N/p-Si structure ranged within 1.516 × 1013 to 1.880 × 1012 eV−1 cm−2 in darkness and 1.699 × 1013 to 1.823 × 1012 eV−1 cm−2 under light.

Current-voltage (I-V) characteristics of Au/n-Ge heterostructure based on cobalt phthalocyanine (CoPc) interlayer

The influence of cobalt phthalocyanine (CoPc) interlayer on the I-V measurements of Au/n-Ge (pristine) contacts is investigated. I-V characteristics reveals the decrease in the reverse leakage current of CoPc interlayer contacts than compared to contacts without interlayer. The Schottky barrier parameters were described using forward I-V measurements by assuming standard thermionic emission mechanism. The barrier height (BH) of the contact with CoPc interlayer is significantly improved than compared to pristine contact. The observed BHs of pristine and CoPc interlayer contacts are found to be 0.63 eV and 0.67 eV respectively. Reduced interface state density and altered space charges on the n-Ge surface reduces tunneling resistance, may account for the larger BH observed in contacts with CoPc interlayer than pristine contacts. The series resistance evaluated for the contacts using Cheung’s method shows its consistency with Norde method. The observed series resistance value of the Au/CoPc/n-Ge contacts found to be significantly smaller in magnitude than Au/n-Ge contacts. The current conduction mechanism of pristine contact and contact with interlayer was evaluated using double logarithmic I-V plot in the forward bias region. Three regions of conduction mechanisms are observed for Au/CoPc/n-Ge contacts. It is evident that the CoPc interfacial layer considerably changes the conduction mechanism from ohmic conduction to trap charge limited current (TCLC) mechanism at moderately high voltages. The associated transition in the conduction mechanism might be due to the presence of shallow traps (low energy traps) with exponential distribution at the CoPc/n-Ge interface.

Вольт-амперная характеристика термоионной эмиссии Na с поверхности Na-=SUB=-x-=/SUB=-Au

In a high-vacuum diode, the volt-ampere characteristic of the thermionic emission of Na+ with surface of NaxAu intermetallide. Its hysteresis was found, which is associated with changes in the surface NaxAu caused by the action of an external electric field. In accordance with the Schottky effect, analysis of the current–voltage characteristic and the value of the work function of the NaxAu surface was estimated. Suggested mechanism of thermionic emission of Na+ from the surface of NaxAu.

Current-voltage characteristic of the thermal ion emission of Na from the Na-=SUB=-x-=/SUB=-Au surface

In a high-vacuum diode, the volt-ampere characteristic of the thermionic emission of Na+ with surface of NaxAu intermetallide. Its hysteresis was found, which is associated with changes in the surface NaxAu caused by the action of an external electric field. In accordance with the Schottky effect, analysis of the current-voltage characteristic and the value of the work function of the NaxAu surface was estimated. Suggested mechanism of thermionic emission of Na+ from the surface of NaxAu. Keywords: intermetallic compound, thermal ionization, Schottky effect.

Hot electron electrochemistry at silver activated by femtosecond laser pulses

A silver microelectrode with a diameter of 30 µm in an aqueous K₂SO₄ electrolyte was irradiated with 55 fs and 213 fs laser pulses. This caused the emission of electrons which transiently charged the electrochemical double layer. The two applied pulse durations were significantly shorter than the electron-phonon relaxation time. The laser pulse durations had negligible impact on the emitted charge, which is incompatible with multiphoton emission. On the other hand, the observed dependence of emitted charge on laser fluence and electrode potential supports the thermionic emission mechanism.

Thermionic performance of nanocrystalline diamond/silicon structures under concentrated solar radiation

Thin films of nanocrystalline diamond with thickness around 100 nm were deposited on highly doped p-type silicon substrates to evaluate the electron emission performance of these structures under illumination of concentrated sunlight in the temperature range 500–700 °C. By comparing the emitted current densities measured using a pure thermal source and a concentrated light source simulating the solar radiation spectrum (Xe lamp), an increase up to about 80 times at 600 °C was found using the concentrated light source, thus demonstrating the boost on the thermionic emission thanks to the sunlight absorption. At temperatures higher than 600 °C the action of the photon-enhanced thermionic emission (PETE) mechanism begins to vanish, starting the regime of pure thermionic emission. The opening of the quasi-Fermi levels reducing the barrier height down to 0.33 eV for electron emission is considered to explain the overall behavior of the diamond-silicon system in the PETE regime.

Effect of Post-Annealing on Barrier Modulations in Pd/IGZO/SiO2/p+-Si Memristors.

In this article, we study the post-annealing effect on the synaptic characteristics in Pd/IGZO/SiO2/p+-Si memristor devices. The O-H bond in IGZO films affects the switching characteristics that can be controlled by the annealing process. We propose a switching model based on using a native oxide as the Schottky barrier. The barrier height is extracted by the conduction mechanism of thermionic emission in samples with different annealing temperatures. Additionally, the change in conductance is explained by an energy band diagram including trap models. The activation energy is obtained by the depression curve of the samples with different annealing temperatures to better understand the switching mechanism. Moreover, our results reveal that the annealing temperature and retention can affect the linearity of potentiation and depression. Finally, we investigate the effect of the annealing temperature on the recognition rate of MNIST in the proposed neural network.

A review on electrical transport properties of thin film Schottky diode

The article outlines an inclusive list of thin film Schottky diodes (TFSD) references. The review audits the fabrication and characterization of the TF metal-semiconductor (MS) diode, a TFSD. The work functions of metal (ϕ m) and semiconducting material (ϕs ) determines whether the established MS contact is ohmic or rectifying. Current-voltage (I – V) and capacitance-voltage (C – V) characterizations are essential electrical transport measures of TFSDs. The I – V and C – V outcomes are conferred, and archetypal results are parroted. The TFSD device is emblematic of a heterojunction diode (HJD). The rectification ratio (RR), saturation current (I0), ideality factor (n), Schottky barrier height (ϕB), and carrier concentration may all be calculated using I – V and C – V data. Thermionic emission (TE) and/or space charge limited conduction mechanisms (SCLC) may conduct electricity in TFSDs. Anderson’s model can theoretically be used to construct a TFSD energy band diagram.

Investigations on interface charge conduction mechanisms for chemically grown manganite – Manganite structure: Hysteretic current – Voltage characteristics

In the present study, high quality LaMnO3–δ/La0·7Ca0·3MnO3/LaAlO3 (LMO/LCMO/LAO) manganite – manganite structure was successfully prepared using low cost chemical solution deposition (CSD) method. Temperature dependent resistive switching (RS) was performed across the manganite – manganite structure and various electronic processes have been employed to understand observed RS behavior. Various theoretical models have been used to understand the charge conduction involved in the hysteretic current – voltage (I–V) characteristics at different temperatures. Charge carrier conduction processes have been investigated for separate I–V cycles of RS characteristics where thermionic emission and space charge limited conduction mechanisms have been identified as appropriate charge carrier conduction mechanisms. Temperature dependent barrier height and other obtained fitting parameters have been discussed in detail.

Optimization of recess-free AlGaN/GaN Schottky barrier diode by TiN anode and current transport mechanism analysis

In this work, the optimization of reverse leakage current (I R) and turn-on voltage (V T) in recess-free AlGaN/GaN Schottky barrier diodes (SBDs) was achieved by substituting the Ni/Au anode with TiN anode. To explain this phenomenon, the current transport mechanism was investigated by temperature-dependent current–voltage (I–V) characteristics. For forward bias, the current is dominated by the thermionic emission (TE) mechanisms for both devices. Besides, the presence of inhomogeneity of the Schottky barrier height (qφ b) is proved by the linear relationship between qφ b and ideality factor. For reverse bias, the current is dominated by two different mechanisms at high temperature and low temperature, respectively. At high temperatures, the Poole–Frenkel emission (PFE) induced by nitrogen-vacancy (V N) is responsible for the high I R in Ni/Au anode. For TiN anode, the I R is dominated by the PFE from threading dislocation (TD), which can be attributed to the decrease of V N due to the suppression of N diffusion at the interface of Schottky contact. At low temperatures, the I R of both diodes is dominated by Fowler–Nordheim (FN) tunneling. However, the V N donor enhances the electric field in the barrier layer, thus causing a higher I R in Ni/Au anode than TiN anode, as confirmed by the modified FN model.

Fabrication and characterization of novel Ga-doped WO3 films and n-Ga@WO3/p-Si junction diode for optoelectronic device applications

In this work, we have fabricated the gallium doped tungsten trioxide (Ga@WO3) films and n-Ga@WO3/p-Si diodes by taking various concentrations (0, 3, 6, 9, and 12 wt%) of Ga through the spin-coating method. To analyze the impact of Ga-dopant on the physical properties of WO3 films, XRD, SEM, and robust dc electrical analyses have been used. From the XRD analysis, compared to the lower concentration of Ga dopant, the higher dopant concentrations show the presence of Ga on the o-GaWO3 crystal structure. The nanoplates-like surface morphology was detected by SEM analysis. The temperature-dependent dc conductivity was studied by I-V characterization, and 12 wt% of Ga doped WO3 thin film exhibits a higher conductivity value and low activation energy (Ea) at room temperature. The J-V nature signifies that n-WO3/p-Si diode performance was enhanced using Ga dopant concentration. The diode constraints ideality factor (n) and barrier height (ΦB) values were determined from J-V, Cheung’s, and Norde's functions. From J-V-T & Richardson plot (ln (J0/T2)), we obtain that the ΦB values were decreased with decreasing temperature. This is explained through the mechanism of thermionic emission with ΦB Gaussian distribution. The determined parameters of the fabricated films and junction diode signify that these can be employed in the applications of photodetectors and solar cells.

A Vacuum Transistor Based on Field-Assisted Thermionic Emission from a Multiwalled Carbon Nanotube

Vacuum triodes have been scaled down to the microscale on a chip by microfabrication technologies to be vacuum transistors. Most of the reported devices are based on field electron emission, which suffer from the problems of unstable electron emission, poor uniformity, and high requirement for operating vacuum. Here, to overcome these problems, a vacuum transistor based on Field-Assisted thermionic emission from individual carbon nanotubes is proposed and fabricated using microfabrication technologies. The carbon nanotube vacuum transistor exhibits an ON/OFF current ratio as high as 104 and a subthreshold slope of ~4 V·dec−1. The gate controllability is found to be strongly dependent on the distance between the collector electrodes and electron emitter, and a device with the distance of 1.5 μm shows a better gate controllability than that with the distance of 0.5 μm. Benefiting from Field-Assisted thermionic emission mechanism, electric field required in our devices is about one order of magnitude smaller than that in the devices based on field electron emission, and the surface of the emitters shows much less gas molecule absorption than cold field emitters. These are expected to be helpful for improving the stability and uniformity of the devices.