Thermionic Emission

Organic light‐emitting diodes were obtained using a thiophene vynilic derivative polymer electrochemically synthesized. The electrochemistry of the thiophene vynilic derivative, 1,5‐bis(2‐thienyl)‐1,4‐pentadien‐3 one (CDV), was conducted in a nonaqueous media. The polymer was deposited on tin oxide (SnO2)‐coated glass substrates. The films obtained were physicochemically characterized by infrared absorption, a scanning microscope, microprobe X‐ray photoelectron analysis, and photoluminescence measurements. It was shown that the coverage efficiency of the films is very high. There is some oxygen contamination, not only at the surface, but also in the bulk of the polymers. The films are photoluminescent with emission between 660 and 720 nm. The current–voltage (I–V) characteristics exhibit a turn‐on voltage at about 2–4 V depending on the film thickness (120–250 nm). The electroluminescence–voltage (EL–V) curve has a similar shape but a shift of 1–2 V toward higher voltage. In the con...

A computational model has been developed in order to explain the anomalies observed in the direct SiC-6H I(V) characteristic diode. These irregularities consist in a thermionic, a generation-recombination, a tunnelling and a leakage electric current contributions. Two kinds of diode's dimensions have been used. For the small one, a good fitting, at all temperatures has been obtained, but for the big one, the fitting was relatively bad, perhaps due to a so important parasite resistance versus potential variation. Even, a high parasite resistance has been encountered near room temperature. From the Richardson plot, it has been extracted a value of the Richardson constant A* very smaller than the theoretical value. A value of the barrier height has also been evaluated.

Laser-Induced Thermionic Vacuum Arc (LTVA) provides a better way to produce uniform metallic thin films than the classical Thermionic Vacuum Arc (TVA) method. In Ti-doped chromium thin films produced using LTVA, the amorphous chromium is superimposed with small bcc chromium nanoparticles. These amorphous/crystalline structures with small crystallites induce lower roughness and electrical resistivity, reducing electron–phonon scattering and increasing charge transport across LTVA thin films. A significant shift in resistivity for the LTVA samples is observed due to electron scattering on the phonon–crystalline structures in the TVA samples which exhibit larger crystallites. Meanwhile, the wettability measurements reveal a higher contact angle, resulting in a lower surface free energy and consecutively lower dissociation energy for the LTVA-produced thin films than the TVA samples.

In this paper, we derive the equations for the current-voltage characteristics of SiC Schottky barrier diodes from the fundamental physics of thermionic emission and tunneling, as the two fundamental current mechanisms. An excellent fit between the model and the experimental data is achieved without the need for empirical fitting parameters, such as the commonly used ideality factor, and with a single set of physically meaningful parameters. This result shows that the current transport in the measured SiC Schottky diodes is not dominated by defects.

A negative electron affinity (NEA) diamond surface is employed as an emitter electrode in a vacuum thermionic energy conversion device in order to mitigate the negative space charge effect. The motive diagram of an NEA device operating at the virtual saturation point is compared to a similar device with a conventional emitter material operating in the space charge limited regime in order to understand how NEA mitigates space charge. Output current characteristics are calculated for various NEA values, and the results are compared to an ideal (no space charge) model. Increasing the value of the NEA causes the output current characteristic to approach that of the ideal model. Motive diagrams for various values of NEA are calculated and used to explain this phenomenon. It is shown that an NEA device can achieve a maximum output power density equal to the maximum output power density of a similar ideal device.

In this study, a simple, efficient, and economical process is reported for the direct synthesis of carbon nanotube (CNT) field emitters on metal alloy. Given that CNT field emitters can be customized with ease for compact and cold field emission devices, they are promising replacements for thermionic emitters in widely accessible X-ray source electron guns. High performance CNT emitter samples were prepared in optimized plasma conditions through the plasma-enhanced chemical vapor deposition (PECVD) process and subsequently characterized by using a scanning electron microscope, tunneling electron microscope, and Raman spectroscopy. For the cathode current, field emission (FE) characteristics with respective turn on (1 μA/cm²) and threshold (1 mA/cm²) field of 2.84 and 4.05 V/μm were obtained. For a field of 5.24 V/μm, maximum current density of 7 mA/cm² was achieved and a field enhancement factor β of 2838 was calculated. In addition, the CNT emitters sustained a current density of 6...

A directly heated thermionic high power electron beam source was constructed. The circular cross-section tungsten line cathode of length 140 mm with diameter 0.9 mm was used. Different gun design parameters were investigated and their results are discussed in detail. A uniform external magnetic field of 50 G was employed for focusing of electron beam at 180 1 deflection. The gun delivers uniform emission current density throughout the emission surface. The dimensions of the electron beam at worksite were comparable with the line cathode. The beam power of 57 kW was successfully achieved well below the saturation limit. The spring action mechanism was especially designed to avoid any cathode deformation. The gun design facilitates the reported length and emitting surface temperature of the cathode to be further increased to obtain higher emission values. The important gun features are operational reproducibility and long time stability. The evaporation rates for stainless steel have been achieved up to 1 kg/hr. An area of (280 Â 120 mm 2 ) could be heat treated with the line source electron beam in few milliseconds. The gun is extremely useful for melting, evaporation and heat treatment.

Electrical characteristics of Pt Schottky contact formed on semipolar (11-22) n-type GaN planes with different Si doping concentration were investigated. Large Si doping to semipolar (11-22) n-GaN led to improved electrical and structural properties, e.g., the Hall mobility (μ) was increased by 35 % and the full width at half maximum (FWHM) of X-ray rocking curves with X-ray incident beam direction of [-1-12 was decreased by 34 %. Thermionic field emission (TFE) theory applied to the forward current-voltage (I-V) curves of fabricated Pt Schottky diodes yielded the Schottky barrier height (ΦB) of 1.64 and 1.84 eV, the tunneling parameter (E00) of 44 and 65 meV, and the ideality factor (n) of 1.83 and 2.57 for the lowly doped and highly doped samples, respectively, indicating that the Si doping affected the carrier transport properties substantially associated with the change of surface states density.

Thermoelectric conversion system, as one of the keys of space nuclear power supply system, is of great significance to the development and application of space nuclear power source. Thermion thermoelectric conversion system is a kind of thermoelectric conversion technology with potential for development, it has simple equipment and compact structure, but its conversion efficiency is limited by the inherent characteristics of the heat ion Energy converter, in order to improve the conversion efficiency of the thermionic energy converter, the thermionic energy converter and thermoelectric generator are coupled. In this paper, the thermionic-thermoelectric generator is taken as the research object, and the thermodynamic analysis and calculation of the thermionic-thermoelectric generator model is carried out by using the existing formula, on the basis of which the appropriate parameters are selected to optimize the system performance.

Thermoelectric conversion system, as one of the keys of space nuclear power supply system, is of great significance to the development and application of space nuclear power source. Thermion thermoelectric conversion system is a kind of thermoelectric conversion technology with potential for development, it has simple equipment and compact structure, but its conversion efficiency is limited by the inherent characteristics of the heat ion Energy converter, in order to improve the conversion efficiency of the thermionic energy converter, the thermionic energy converter and thermoelectric generator are coupled. In this paper, the thermionic-thermoelectric generator is taken as the research object, and the thermodynamic analysis and calculation of the thermionic-thermoelectric generator model is carried out by using the existing formula, on the basis of which the appropriate parameters are selected to optimize the system performance.

We analyze the operation of a resonant detector of terahertz (THz) radiation based on a two-dimensional electron gas (2DEG) channel with split gates. The side gates are used for the excitation of plasma oscillations by incoming THz radiation and control of the resonant plasma frequencies. The central gate provides the potential barrier separating the source and drain portions of the 2DEG channel. Two possible mechanisms of the detection are considered: (1) modulation of the ac potential drop across the barrier and (2) heating of the 2DEG due to the resonant plasma-assisted absorption of THz radiation followed by an increase in thermionic dc current through the barrier. Using the device model, we calculate the frequency and temperature dependences of the detector responsivity associated with both dynamic and heating (bolometric) mechanisms. It is shown that the dynamic mechanism dominates at elevated temperatures, whereas the heating mechanism provides larger contribution at low temp...

Proper description of the electrical behavior of miniaturized devices requires better understanding of the breakdown phenomena in microgaps (< 10µm) at atmospheric pressures. In microgaps the breakdown characteristics deviate from those defined by the Paschen's law. It is now well accepted that the departure from Paschen's law is due to the contribution of field electron emission. Apart from the small distance, the presence of protrusions on the cathode surface can largely intensify this phenomenon. In this work, the electric field distribution is simulated in needle-plate configuration in presence of various nanoprotrusions on the cathode surface. The purpose is to find conditions when the nanoprotrusions can initiate field electron emission due to a local enhancement of the electric field. The maximum electric field is determined by the location and the geometry of the nanoprotrusions. Surprisingly, for a semi-circle shape of nanoprotrusions, the maximum electric field does not depend on the size of nanoprotrusions.

Temperature dependences of the series resistance in the Cr/n-Si/Au-Sb Schottky structures prepared by electrodeposition method have been studied using current-voltage (I-V) characteristics in the 80-320 K temperature range by steps of 20 K. However, the values of series resistance obtained from Cheung functions were compared with each other, and it was seen that there is a good agreement between the values of the series resistance. A modified Norde's function combined with conventional forward I-V method was used to extract the parameters including barrier height and the series resistance. The barrier height and series resistance obtained from Norde's function were compared with those from Cheung functions. The values of barrier height and series resistance have very different especially towards to the lower temperatures. This is attributed to non-ideal I-V characteristics of the Cr/n-Si/Au-Sb Schottky structure and non-pure thermionic emission theory due to the low temperature effects.

Al device has been fabricated and its currentvoltage (I-V) characteristics measured between 80 K and 460 K. Junction parameters of the device, such as the ideality factor, barrier height, interface state density, and series resistance (R s ), were determined using standard thermionic emission theory, the Cheung function, and the Norde method. The application of these approaches revealed that n varied between 4.66 and 1.70 in the temperature range of 80 K to 460 K, while U b varied between 0.24 eV and 0.83 eV in the same temperature range. These variations of n and U b can be attributed to the barrier height inhomogeneity in the device. Although PR is generally used in biological applications such as cell culture, it has been observed that such Co/phenol red/n-Si/Al devices may be critical candidates for use in thermal sensors and photodiode applications due to their photoresponse and low-temperature operation for reverse-bias I-V measurements. Furthermore, PR is an alternative to semiconductor materials commonly used in such applications.

We employed hematoxylin as interfacial layer between the n-and p-type silicon substrate and cobalt (Co) metallic contact to obtain and compare Co/hematoxylin/n-Si and Co/hematoxylin/p-Si devices for a wide range temperature via current-voltage (I-V) characteristics. Furthermore, we studied structural and morphological properties of the hematoxylin thin film by x-ray diffractometer (XRD) and scanning electron microscope (SEM). The temperature range was changed from 100 K to 460 K via 20 K interval for I-V measurements. The Co/hematoxylin/n-Si and Co/hematoxylin/p-Si devices exhibited excellent rectifying behaviors for low temperatures, but rectifying ratio (RR) values decreased with increasing temperature at �1 V bias. In addition, the devices showed thermal sensor or detector behavior because current values increased with increasing temperature at reverse biases. The Co/hematoxylin/p-Si device has better stability than Co/hematoxylin/n-Si device at reverse biases for the same temperature values according to stop leakage current with increasing voltage. In addition, the diode parameters such as barrier height, ideality factor and series resistance as well as interface states density were extracted from the I-V measurements and compared in details for various techniques such as thermionic emission theory, Norde and Cheung methods. The diode parameters of the both devices were affected from the temperature changes. The Co/hematoxylin/n-Si and Co/hematoxylin/p-Si devices are good candidate for rectifying and thermal sensing applications.

The temperature dependence of the current–voltage and room temperature capacitance–voltage measurements of Co/aniline blue/ n-Si sandwich-type rectifying device was investigated.Furthermore, the effects of the illumination on the current–voltage measurements were tested with 100 mW/cm2 light intensity, and it was seen that Co/aniline blue/ n-Si sandwich-type device showed a clear response to illumination, and it may be a candidate for solar cells or photodiode applications. The rectifying device parameters, such as the barrier height (Ф), the ideality factor ( n), the rectification ratio, and the series resistance ( Rs), were obtained as a function of temperature using thermionic emission, Cheung function, and Norde function. The interface state densities versus energy were obtained. The Richardson constant ( A*) obtained from the In( Io/ T2) versus 1000/ T plot was much less than the theoretical value for n-Si. The mean Schottky barrier height[Formula: see text] and the standard de...

Experimental study of the diffuse vacuum arc discharge on the nonthermionic lead cathode is presented. At the working cathode temperatures of 1.2-1.6-kK currentvoltage characteristic of the discharge, cathode heat operation regime and its erosion rate were measured. Using probe methods, electron temperature (0.3-1.2 eV) and heavy particles (atoms and ions) mean charge (0.17-0.28 e) were determined in afteranode plasma. Evaluated current densities on the cathode are in agreement with a hypothesis on the ion mechanism of charge transfer on its surface. Parameters of the obtained discharge have been compared with the characteristics of the earlier investigated diffuse vacuum arcs on nonthermionic chromium and on thermionic gadolinium cathodes. The obtained data might be useful when creating plasma sources for verifying the plasma separation method of the spent nuclear fuel using the nonradioactive substances.

As previously demonstrated, contact-electrification (CE) is strongly dependent on temperature, however the highest temperature in which a triboelectric nanogenerator (TENG) can still function is unknown. Here, by designing and preparing a rotating free-standing mode Ti/SiO TENG, the relationship between CE and temperature is revealed. It is found that the dominant deterring factor of CE at high temperatures is the electron thermionic emission. Although it is normally difficult for CE to occur at temperatures higher than 583 K, the working temperature of the rotating TENG can be raised to 673 K when thermionic emission is prevented by direct physical contact of the two materials via preannealing. The surface states model is proposed for explaining the experimental phenomenon. Moreover, the developed electron cloud-potential well model accounts for the CE mechanism with temperature effects for all types of materials. The model indicates that besides thermionic emission of electrons, t...

A Schottky diode based on a heterojunction of three-dimensional (3D) nanohybrid materials, formed by hybridizing reduced graphene oxide (RGO) with epitaxial vertical zinc oxide nanorods (ZnO NRs) and Al0.27GaN0.73(∼25 nm)/GaN is presented as a new class of high-performance chemical sensors. The RGO nanosheet layer coated on the ZnO NRs enables the formation of a direct Schottky contact with the AlGaN layer. The sensing results of the Schottky diode with respect to NO2, SO2, and HCHO gases exhibit high sensitivity (0.88-1.88 ppm(-1)), fast response (∼2 min), and good reproducibility down to 120 ppb concentration levels at room temperature. The sensing mechanism of the Schottky diode can be explained by the effective modulation of the reverse saturation current due to the change in thermionic emission carrier transport caused by ultrasensitive changes in the Schottky barrier of a van der Waals heterostructure between RGO and AlGaN layers upon interaction with gas molecules. Advances i...

In this paper, we investigate the presence of minority carriers and their role in charge carrier transport in silicon (Si) Schottky diodes with a high potential barrier. Using TCAD simulations along with an analytical model, we show that an inversion charge is induced at the metal-semiconductor (MS) interface in a high-barrier Schottky diode which imparts bipolar-type current characteristics to otherwise a unipolar Schottky diode, even at low-injection operation. In such a high-barrier diode, minority diffusion also becomes important along with the majority carrier thermionic emission and therefore cannot be neglected, unlike in a conventional Schottky diode. The presence of minority carriers at low injection in a high-barrier Si Schottky diode has been experimentally verified via a prior-reported two-diode electrical test method, reverse recovery measurements, and by measuring infrared electroluminescence. It is also shown, via TCAD simulations, that the diffusion component becomes more pronounced in case of a reduced Gummel number and at elevated temperatures.

An overview is presented of planned future directions of thermionic energy conversion research for the next decade. The primary focus will be on space nuclear power applications in the ten to thousand k W range. In addition to refining the state of the art for the conventional ignited mode converter, there are more generic technologies which will be pursued for a wide range of duty cycles.

β-Ga 2 O 3 thin films were grown on n-type GaN substrates using the sol-gel method. The forward-biased temperature dependent current-voltage (I-V-T) characteristics of Ni/β-Ga 2 O 3 /GaN structure have been investigated in the temperature range of 298-473 K. The apparent barrier height ( ap ) increased while the ideality factor (n) decreased with the increase in temperature. Such a temperature dependent behavior of ap and n was explained by the inhomogeneity of ap , which obeyed Gaussian distribution with zero-bias mean barrier height ( φB0 ) of 1.02 ± 0.02 eV and standard deviation ( s0 ) of 153 ± 0.04 mV. Subsequently, φB0 and Richardson constant A * were obtained from the slope and intercept of the modified Richardson plot as 0.99 ± 0.01 e V and 67.2 A cm -2 K -2 , respectively. The φB0 obtained from the modified Richardson plot was in good agreement with the theoretical value calculated from the work function of Ni and electron affinity of β-Ga 2 O 3 . The I-V-T characteristics of Ni/β-Ga 2 O 3 /GaN MOS structures can be successfully explained by the thermionic emission theory with a single Gaussian distribution of the barrier height.

During the last years, high-k dielectrics have been studied intensively looking for an alternative material to replace the SiO 2 films as gate dielectric in MOS transistors. Different materials and structures have been proposed. An important concern not yet solved, is the interfacial quality between high-k materials and silicon substrate. For this reason, stack structures with SiO 2 as an interfacial layer between silicon substrate and high-k film have been studied. In this contribution we analyze the main conduction mechanism observed in SiO 2 /TiO 2 MOS stack structures obtained by room temperature plasma oxidation in different conditions and reactors. Films fabricated in a parallel-plate type reactor showed better quality with low current density where thermionic conduction mechanism is predominant. In lower quality films, for example those fabricated in a barrel type equipment, the current density is higher and the conduction mechanism observed is Poole-Frenkel. Finally we show that the presence of thermionic mechanism provides a weak thickness dependence and a strong current density reduction with respect to silicon oxide MOS structures with the same equivalent oxide thickness.

Quantum dot infrared photodetectors (QDIPs) have many advantages over other types of semiconductor-based photodetectors. However some of its characteristics have been investigated theoretically, there are many unstudied points. In this paper a new approach is presented to evaluate quantum dot infrared photodetectors dark current and photocurrent. In this study, it is assumed that both thermionic emission and field-assisted tunneling mechanisms determine the dark current of quantum dot detectors. Based on these assumptions, new formula for average number of electron in a quantum dot for both, dark and illumination condition is calculated, which is more accurate than the previous reported formulas; because in deriving previous reported formulas, it was assumed only thermionic emission determines dark current but field-assisted tunneling mechanisms has not been considered. Then numerical method is used to calculate the average number of electron in a quantum dot and to determine dark current and photocurrent. The theoretical results are compared with experimental data. They have good agreement with available experimental data.

We report on ohmic contact measurements of Al, Au, and W metallizations to p-type epitaxial Ge 0:9983 C 0:0017 grown on a (100) Si substrate by molecular beam epitaxy (MBE). Contacts were annealed at various temperatures, and values of specific contact resistance have been achieved which range from 10 05 1 cm 2 to as low as 5:6 2 10 06 1 cm 2 . Theoretical calculations of the contact resistance of metals on Ge10xCx with small percentages of carbon, based on the thermionic field emission mechanism of conduction, result in good agreement with the experimental data. We conclude that Al and Au are suitable ohmic contacts to p-Ge0:9983C0:0017 alloys.

To understand the nature of low-frequency gain in MSM photodiodes, Schottky barrier height was measured for an barrier height showed a dependence on the light irradiation and due to charge accumulation at surface states and image-force lowering at the edges of metal electrodes where electric field is extremely high. Thermionic hole emission is proposed as a source of low-frequency gain of MSM photodiodes. The low-frequency gain can be suppressed by preserving a nonabsorbing layer under the metal electrodes [3], [6]. In MSM photodiode fabricated on GA-based layers. The Schottky addition to the proposed electron tunneling enhanced by hole trapping at the cathode, the being reported in this bias. This can be explained by a lowering of the Schottky barrier

For the perovskite halides, current voltage hysteresis is the biggest puzzle to be solved before industrialization in spite of promising features for future photo-voltaic applications. All the possible causes, from the classical (viz., morphology, defects, slow transient capacitance, etc.) to quantum (viz., spin–orbit interaction) ones, are investigated. However, its origin is still under debate, as possibilities showed some ambiguity on the science known until now. In the present work, we have studied the time dependent photo-conduction behavior of CsPbBr3 in continuous illumination of AM 1.5 G Sun light for 3 h. We observed a negative differential resistance for a forward scanned current–voltage curve in AM 1.5 G Sun light. Our investigations suggest that the photo-current voltage hysteresis is primarily affected by the thermionic-field emission, which slows down the drift velocity of hot charge carriers with field applications. This study will further lead the scientific communit...

ZnO thin films with the n-type properties were obtained on the p-Si substrates for multi-layered sandwich device depositing by sol-gel method. Au and Al were conducted on two side of hetero-junction by PVD technique. From X-ray diffraction pattern, a strong (002) direction is observed, which means the film is hexagonal texture. Cross-section image from the scanning electron microscope demonstrated that the coated ZnO films had ~ 427 nm thickness. Electrical behavior of the device was characterized by applying voltage versus current. High purity Au and Al metals were vacuum evaporated to make Schottky and Ohmic contacts onto the device. Au/n-ZnO/p-Si/Al architecture exhibited a rectification behavior. According to Thermionic emission mechanism theory, barrier height and ideality factor of device were found as 1.4 and 0.54 eV, respectively. The series resistance values were obtained from dV/d(lnI) versus I and H(I) versus I graphs as 43.6 Ω and 229.9 Ω, respectively.

We present a new semi-empirical model for calculating electron transport in atomic-scale devices. The model is an extension of the Extended Hückel method with a self-consistent Hartree potential. This potential models the effect of an external bias and corresponding charge re-arrangements in the device. It is also possible to include the effect of external gate potentials and continuum dielectric regions in the device. The model is used to study the electron transport through an organic molecule between gold surfaces, and it is demonstrated that the results are in closer agreement with experiments than ab initio approaches provide. In another example, we study the transition from tunneling to thermionic emission in a transistor structure based on graphene nanoribbons.

A thermionic triode rf gun is being developed to mitigate the adverse effect of electron back-bombardment onto the cathode inherent in conventional rf guns. An coaxial rf cavity with a thermionic cathode on the inner rod of the coax was designed and fabricated, which is to be installed in an existing conventional rf gun to configure the rf triode structure. The rf coupler geometry between the coaxial cavity and the rf waveguied was designed by use of a 3-D electromagnetic field solver. Numerical comparisons were made between two candidates, namely W and LaB 6 , for the thermionic cathode material. As the result, unlike in the conventional rf gun, W cathode is found to enable a longer macro-pulse duration for the same back-bombardment power. Expected macro-pulse duration by the triode rf gun is twice as long as the conventional gun with ~10 times higher peak current without degradation in emittance.

CdSe capped with Tri sodium citrate (TSC), nanoparticles were organized by chemical process at ambient conditions. Spin casting technique was used to deposit thin films on substrates from glass at room temperature. Schottky junctions have been fabricated by depositing CdSe thin films using the spin coating on Aluminum (Al) and Florien Tin Oxide (FTO) coated glass substrates and their properties have been investigated by current–voltage measurements. The characteristics obey the pure thermionic emission theory and the contact showed a good rectifying behavior in both structures.

Charge injection and retention in thin dielectric layers remain critical issues for the reliability of many electronic devices because of their association to a large number of failure mechanisms. To overcome this drawback a deep understanding of the mechanisms leading to charge injection close to the injection area is highly demanded. Even though the charge injection is extensively studied and reported in the literature to characterize the charge storage capability of dielectric materials, questions about charge injection mechanisms when using Atomic Force Microscopy (AFM) remain open. In this paper, a thorough study of charge injection by using AFM in thin plasma processed amorphous silicon oxynitride layers with properties close to that of thermal silica layers is presented. The study considers the impact of applied voltage polarity, work function of the AFM tip coating and tip curvature radius. A simple theoretical model was developed and used to analyze the obtained experimental results. The electric field distribution is computed as a function of tip geometry. The obtained experimental results highlight that after injection in the dielectric layer the charge lateral spreading is mainly controlled by the radial electric field component independently on the carrier polarity. The injected charge density is influenced by the nature of electrode metal coating (work function) and its geometry (tip curvature radius). The electron injection is mainly ruled by the Schottky injection barrier through field electron emission mechanism enhanced by thermionic electron emission. The hole injection mechanism seems to differ from the electron one in the dependence on the work function of the metal coating. Based on the performed analysis, it is suggested that for hole injection by AFM, pinning of the metal Fermi level with the metal-induced gap states in the studied silicon oxynitride layers starts playing a role in the injection mechanisms.

A simple, MEMS base micro-chemical detector utilizing the principles of gas ionization, has been designed and fabricated. The device contains a polysilicon micro air-bridge heater structure with integrated polysilicon electrodes. The design of the devices allows it not only functions via thermionic emission, but also via chemi-ionization if a proper Pt catalyst is applied and it is operated in an environment containing hydrogen. When properly biased the device has been shown to heat to high temperatures where thermionic emission can begin to occur. Hydrocarbon chemicals in the gas phase have shown to ionize, via thermionic ionization and have been collected, producing a measurable current signal.

ABSTRACTThe piezoresistive properties of boron-doped PECVD microcrystalline Si films (μc-Si) deposited on SiO2 coated Si, covar or quartz substrates have been investigated. The relations between the gauge factor (G.F.) and doping concentrations as well as the film thickness etc. have been obtained experimentally. The maximum longitudinal G.F. of 25 and 20 are measured for Si and covar substrates respectively. An expression for calculating G.F. of P-type μc-Si is derived theoretically by use of the splitting model of heavy and light hole band at k=0 and the thermionic emission theory. The calculated dependences of G.F. on the doping concentrations, grain size and trap state density agree well with the experimental results, which offer a better understanding of the piezoresistive characteristics of μc-Si or poly-Si, and enable optimized design and fabrication of μc-Si or poly-Si strain gauges.

Although a thermionic RF gun is compact and economic, it is difficult to produce electron beam of pulse width longer than a few μsec with constant energy owing to inherent back-bombardment effect. In this work we tried to keep beam energy constant in macro pulse duration by feeding modulated RF power. We also tried to perform transient analysis with equivalent circuit taking into account the back-bombardment effect in macro pulse duration. We found that the degradation of the peak energy of the beam could be kept below 100 keV in the macro pulse duration of 8μsec.

A thermionic triode rf gun is being developed to mitigate the adverse effect of electron back-bombardment onto the cathode inherent in conventional rf guns. An coaxial rf cavity with a thermionic cathode on the inner rod of the coax was designed and fabricated, which is to be installed in an existing conventional rf gun to configure the rf triode structure. The rf coupler geometry between the coaxial cavity and the rf waveguied was designed by use of a 3-D electromagnetic field solver. Numerical comparisons were made between two candidates, namely W and LaB 6 , for the thermionic cathode material. As the result, unlike in the conventional rf gun, W cathode is found to enable a longer macro-pulse duration for the same back-bombardment power. Expected macro-pulse duration by the triode rf gun is twice as long as the conventional gun with ~10 times higher peak current without degradation in emittance.

Metal/semiconductor structures, particularly Schottky diodes, play a crucial role in semiconductor identification and the production of electronic devices, like solar cells, photodetectors, photodiodes, and field-effect transistors (FETs). These structures are of great interest due to their ability to modify electrical and optical properties, responding to external factors such as illumination and temperature. However, despite extensive research in this field, there has been limited exploration of silicon-based metal/semiconductor structures incorporating PANI:Borophene interfacial materials. In this study, we prepared PANI:Borophene/p-Si and PANI:Borophene/n-Si structures and examined their photodiode properties using various measurements. The unoccupied trap levels (m) obtained 0.44 and 0.33 for Al/PANI:Borophene/p-Si and Au/PANI:Borophene/n-Si device, respectively. Our investigation revealed that both structures exhibited rectification behavior, with linear characteristics in the forward bias region, and deviations attributed to series resistance effects at higher voltages. Moreover, the presence of borophene in the interfacial layer led to improvements in the devices' electrical properties. Finally, the PANI:Borophene/Si Schottky diodes was tested for salt detection and the Al/ PANI:Borophene/p-Si diode has the characteristics of salt (NaCl) concentration

An AlInP delta-doped schottky diode exhibiting negative differential resistance (NDR) behavior is demonstrated for the first time. The NDR characteristics with a peak to valley ratio of 5.5 and peak current density of1KA/cm2were achieved at room temperature. In addition, the maximum available power is estimated up to5W/cm2. The mechanism for such performance is phenomenologically analyzed by the combination of resonant interband tunneling (RIT) and thermionic emission processes associated with tunneling effect on the metal-semiconductor (MS) interface.

A deep analysis of conductance in nanostructured thick films has been performed. A model for field-assisted thermionic barrier crossing is being proposed to explain the film conductivity. The model has been applied to explain the behavior of resistance in vacuum of two sets of nanostructured thick-films with grains having two well-distinct characteristic radii ( nm and  nm). In the first case the grain radius is shorter than the depletion region width, a limit at which overlapping of barriers takes place, and in the second case it is longer. The behavior of resistance in the presence of dry air has been explained through the mechanism of barrier modulation through gas chemisorption.

Recibido el 4 de junio de 2010; aceptado el 9 de febrero de 2011 The charge transport mechanisms occurring in n-type a-SiGe:H on p-type c-Si heterojunctions were determined by analyzing the temperature dependence of the current-voltage characteristics in structures with four different peak base doping concentrations (N B = 1×10 15 , 7×10 16 , 7×10 17 and 5×10 18 cm −3). From the experimental results, we observed that at low forward bias (V< 0.45V) the current is determined by electron diffusion from the n-type amorphous film to the p-type c-Si for the heterojunction with N B = 1×10 15 cm −3 , whereas the Multi-Tunneling Capture Emission (MTCE) was identified as the main transport mechanism for the other base doping concentrations. On the other hand, at high forward bias (V> 0.45V), the space charge limited current effect became the dominant transport mechanism for all the measured devices. Under reverse bias the transport mechanisms depends on the peak base doping, going from carrier generation inside the space charge region for the lowest doping, to hopping and thermionic field emission as the base doping concentration is increased.

The knowledge of the conduction mechanisms in a Schottky barrier is essential to calculate the Schottky barrier parameters and to explain the observed effects. In the present work, we report temperaturedependent current-voltage characteristics of (Mo/Au)/Al 0.26 Ga 0.74 N/GaN/Si/ Schottky barrier diodes. Measurements were performed in the temperature range of 80 -300 K.Results have been explained based on the thermionic emission mechanism with lateral inhomogeneity at the (Mo/Au/AlGaN/GaN/Si) interface. As is shown, the barrier height Φ B0 as well as the ideality factor n exhibit an important temperature dependence and the anomaly resulting from this dependence has been explained by invoking two sets of Gaussian distributions at the metal/semiconductor interface for temperature ranging from 80 K to 160 K and from 160K to300 K, respectively. It is also found that the values of R s obtained from Cheung's method strongly depend on temperature and decrease with decreasing temperature.

We discuss models to describe carrier transport in axial and lateral type carbon nanotube field-effect transistors (CNT-FET). Operation is controlled by the electric field from the gate contact which can lead to strong band bending allowing carriers to tunnel through the interface barrier. We find that the difference between lateral and axial CNT-FETs is that in devices with axially aligned carbon nanotubes tunneling becomes negligible and transport can be modeled by means of thermionic emission. In lateral CNT-FETs tunneling dominates for which we present a model for the transmission coefficient using the WKB method and a non-parabolic dispersion relation. The simulated output and transfer characteristics show reasonable agreement with experimental data for both lateral and axial CNT-FET devices.

Barium fluoride thin films (0.1-500 nm) were deposited on GaAs. � Photoemission highlights the presence of a dipolar surface interaction. � Work function drops to 2.1 eV for a film thickness of 2.0 nm. � Films are transparent in the 500-2500 nm wavelength range. � Thermionic measurements on test devices confirm films reliability at high temperature.

We have measured the dependence of the Fermi energy on carrier concentration in Sn doped InGaAs at 4.2 K and 300 K. At 4.2 K the Fermi energy was measured by photoluminescence spectroscopy, and at 300 K it was deduced from transport measurements of thermionic emission. In both cases the dependence of the Fermi energy on the mobile electron concentration, measured by Hall effect, strongly deviates from standard theoretical predictions, and the deviation increases with concentration. The most striking observed anomaly is the near saturation of the Fermi level when the Hall concentration exceeds 10 19 cm -3 .

We describe a method of Fermi energy measurement, based on the analysis of thermionic emission and diffusion over a barrier with a built-in charge. The method can be applied to a variety of semiconductors and has been successfully tested by measuring the Fermi energy in GaAs.

KICOS) through a grant provided by the Korea Ministry of Education, Science & Technology (MEST) (GPP K20602000006-07E0200-00610) is gratefully acknowledged. Y.T. and E.E.B.C. acknowledge the support of the European Commission through the FP6 grant NanoRF. This publication reflects the views of the authors and not necessarily those of the EC. The EC is not liable for any use that may be made of the information contained herein.

A series of photonic crystal structures are optimized for a photon enhanced thermionic emitter. With realistic parameter values to describe a p-type GaAs device we find an efficiency above 10%. The light-trapping structures increases the performance by 2% over an optimal bilayer anti-reflective coating. We find a device efficiency very close to the case of a Lambertian absorber, but below its maximum performance. To prevent an efficiency below 10% the vacuum gap must be dimensioned according to the concentration factor of the solar irradiance.