Papers by Nikolaos Georgoulas
Graphene oxide (GO) is a promising material for various sensing applications. In this contributio... more Graphene oxide (GO) is a promising material for various sensing applications. In this contribution we propose a humidity sensing device based on GO grown on glass substrate. Different devices were fabricated in order to investigate the effect of deposition parameters to sensing capabilities of GO. Furthermore, thermal annealing process was applied to turn GO to reduced graphene oxide and measure its behavior as a humidity sensor
Journal of Semiconductors, 2017
A parametric study for a series of technological and geometrical parameters affecting rise time o... more A parametric study for a series of technological and geometrical parameters affecting rise time of Al/a-SiC/c-Si (p)/c-Si (n+)/Al thyristor-like switches, is presented here for the first time, using two-dimensional simulation techniques.By varying anode current values in simulation procedure we achieved very good agreement between simulation and experimental results for the rising time characteristics of the switch.A series of factors affecting the rising time of the switches are studied here.Two factors among all others studied here, exerting most significant influence, of more than one order of magnitude on the rising time, are a-SiC and c-Si (p) region widths, validating our earlier presented model for device operation.The above widths can be easily varied on device manufacture procedure.We also successfully simulated the rising time characteristics of our earlier presented simulated improved switch, with forward breakover voltage VBF=11 V and forward voltage drop VF=9.5 V at the ON state, exhibiting an ultra low rise time value of less than 10 ps, which in conjunction with its high anode current density values of 12 A/mm2 and also cheap and easy fabrication techniques, makes this switch appropriate for ESD protection as well as RF MEMS and NEMS applications.
Journal of Power Sources, 2015
We grew amorphous silicon in micrograin structure by DC sputtering on copper foil. Irreversible c... more We grew amorphous silicon in micrograin structure by DC sputtering on copper foil. Irreversible capacity below 20% in the first lithiation-delithiation cycle. Anodes with stable specific capacity up to 2.0 mAh cm À2 are achieved. Structural morphology of silicon and electrochemical performance are correlated.
Journal of Applied Physics, 1998
In the present work, the effect of rapid thermal annealing (RTA) on the electrical and structural... more In the present work, the effect of rapid thermal annealing (RTA) on the electrical and structural properties of poly-Si thin films, grown by the crystallization of a-Si films deposited by rapid thermal low-pressure chemical vapor deposition, has been studied. Structural and electrical results were obtained using atomic force microscopy, transmission electron microscopy, electron spin resonance, electrical resistivity, and Hall mobility techniques. The effects of the grain size, grain boundaries, and surface roughness on the electrical characteristics of poly-Si films have been investigated. Amorphous Si (a-Si) films crystallized by RTA at 850 °C for 45 s result in the formation of poly-Si with small grains, an electron spin density Ns=5.2×1016 cm−3, and a Hall mobility μH=30 cm2 V−1 s−1. A two-stage annealing, involving low-temperature annealing at 600 °C for 6 h, followed by RTA at 850 °C in five steps of 30 s each, results in the formation of poly-Si films with large grains free o...
Active and Passive Electronic Components, 1998
The a-SiC/c-Si(n) isotype heterojunction has been studied as a temperature sensor by measuring it... more The a-SiC/c-Si(n) isotype heterojunction has been studied as a temperature sensor by measuring its reverse current-voltage (IR-V) and reverse voltage-temperature (V-T) characteristics, as well as its reverse current temperature dependence. The IR-V characteristics exhibit an almost constant current, whereas the reverse current Ia depends strongly on T (from 230 K up to 320K). The V-T characteristics, at different reverse currents, reveal a highly temperature sensitive behavior for the a-SiC/c-Si(n) junction. The measured values of temperature sensitivity (A V/AT) was found to be (-2.5 V/K) in the moderate temperature range, which are much higher than those obtained with bulk semiconductor temperature sensors. The high sensitivity-temperature-range of the a-SiC/c-Si(n) heterojunctions can be controlled electrically within the regim of values from 230 K up to 320 K. Finally, the high sensitivity of these devices, in conjunction with the fact that a-SiC films can be used as an add-on to the existing Si technology, emerge new possibilities to the fabrication of high sensitivity temperature microsensors.
IEEE Electron Device Letters, 1982
... A non-Schottky-diode in which the carrier transport is controlled by a potential barrier in t... more ... A non-Schottky-diode in which the carrier transport is controlled by a potential barrier in the bulk of the ... lb), and if the loss is described by the storage time 7, then the light induced change of the ... According to (4), An modulates the potential barrier and hence the diode current: (4) ...
The size and distribution of defects, the dopant diffusion and the electrical activation of rapid... more The size and distribution of defects, the dopant diffusion and the electrical activation of rapidly thermally processed arsenic implanted silicon, in the temperature range between 650 and 950 °C, have been studied using TEM measurements, as well as secondary ion mass spectrometry (SIMS), sheet resistance methods, and differential Hall effect measurements. The arsenic atomic profiles are governed by concentration dependent diffusion. There is no evidence of an initial transient enhanced diffusion (TED). The electrical activation efficiency is about 60 %, at 650 °C/10s. At 950 °C, a fraction of the dopant is lost from the surface, due to the out-diffusion, resulting in a reduction in the active dose, which causes an increase of about 33 % in sheet resistance, for annealing time of 20 s. n + p diode characteristics deviate from ideal behavior, exhibiting high reverse leakage current densities (8.5.10 -7 -7.0.10 -8 A/cm2), which may be attributed to the residual implantation defects.
Microelectronics Reliability, 2005
Experimental investigation of the substrate current I sub as a function of the gate voltage has b... more Experimental investigation of the substrate current I sub as a function of the gate voltage has been performed in n-channel polycrystalline silicon thin-film transistors (polysilicon TFTs), considering the drain voltage as a parameter of the study. At low gate voltages, I sub exhibits a peak located close to the threshold voltage of the transistor due to hotcarriers generated by impact ionization. At higher gate voltages, I sub increases monotonically with increasing the gate voltage, which is attributed to the temperature rise owing to self-heating. The degradation behavior of polysilicon TFTs, stressed under two different gate and drain bias conditions that cause the same substrate current due to hotcarrier and self-heating effects, is investigated.
Thin Solid Films, 2002
In this paper, an extensive study of the photocurrent amplification mechanism of silicon bulk-bar... more In this paper, an extensive study of the photocurrent amplification mechanism of silicon bulk-barrier diodes (BBDs) is presented, based on simulation and experimental results. As a result of this study an analytical model is proposed. The proposed model extends previously published models and includes analytical expressions for all significant quantities of the device optoelectronic behaviour. Such quantities are barrier lowering, photocurrent, quantum efficiency and response speed as functions of the applied voltage, incident light power, light wavelength and modulation frequency, as well as a function of technological parameters. Simulation and experimental results verify the validity of the proposed analytical model, and they show that BBDs are majority carrier photodetectors with high internal photocurrent gain. Compared with common photodetectors, BBDs exhibit a very high sensitivity in the blue region of the visible spectrum.
Superlattices and Microstructures, 1998
ABSTRACT
Microelectronics Journal, 1997
Electrical properties of Schottky diodes on rf sputtered a-SiC:H thin films for different metals ... more Electrical properties of Schottky diodes on rf sputtered a-SiC:H thin films for different metals (Mg,In,Al,Pd) were investigated. The M(=Mg,In,A1,Pd)/a-SiC:H Schottky diodes were found to exhibit very good rectification properties, with a turn-on voltage varying from 0-4 to 0-8V, depending on the top metal used, and a reverse current density lower than 10-gA/cm 2 with a reverse break down voltage, V3, approximately equal to 15V. The ideality factor, ~/, was found to be 1.34-0.1. This, combined with the temperature dependence of I-V characteristics, indicates that thermionic emission is most likely the dominant transport mechanism. A linear increase of barrier height at room temperature, ~%RT, with increasing metal work function, ~0r~, was obtained, suggesting that a-SiC:H exhibits the same type of conductivity (n-type) as that found for non-hydrogenated a-SiC. Pd/a-SiC:H Schottky diodes were found to exhibit linear room temperature log I vs V characteristics, over eight orders of magnitude, making these devices suitable for many applications.
Materials Science and Engineering: B, 2004
ABSTRACT The generation and the evolution of extended defects in ultra-shallow n+–p junctions, fo... more ABSTRACT The generation and the evolution of extended defects in ultra-shallow n+–p junctions, formed by As ion implantation into silicon at low energies of 15, 10 and 5 keV and a dose of 1 × 1015 cm−2, and rapid thermal annealing (RTA) at temperatures of 650 °C ≤ T ≤ 950 °C have been studied using transmission electron microscopy (TEM) measurements. The generated defects in the end-of-range region are dislocation loops, which grew larger and their density decreased with increasing annealing temperature. Reduction in the implantation energy causes a decrease in defect size and density as well as in dissolution temperature. The loops dissolved at 950 °C for 15 and 10 keV, whereas for 5 keV they dissolved at 850 °C. Arsenic transient enhanced diffusion (TED) studied by ToF–SIMS measurements was observed at temperatures above 650 °C for all implantation energies, with markedly less TED for the 5 keV, although As segregates near the surface region. The results suggest that the surface plays a key role on the formation and the dissolution of the dislocation loops and the As TED, by acting as a perfect sink of point defects. A significant degradation in electrical activation efficiency and a sharp increase in sheet resistance were observed at the low energy of 5 keV. In addition, the increase of temperature causes a slight decrease in electrical activation efficiency. Out-diffusion of As (10–25%) plays a significant role in the electrically active fraction of the dopant, due to the extreme proximity to the surface of high As concentrations. Junctions shallower than 40 nm, with 50–40% of the implanted dose electrically active and sheet resistance of 370–320 ohm/square, were obtained for the 5 keV. Finally, the TED during RTA was correctly simulated using a RTA model implemented in SSUPREM4 of the process simulator, including the dislocation loops and the dose loss.
Journal of Non-Crystalline Solids, 1992
In this work the dependence of structural, compositional, and optical properties of sputtered a-S... more In this work the dependence of structural, compositional, and optical properties of sputtered a-SiC:H thin films on substrate temperature, Ts, and hydrogen flow rate have been measured, a-SiC:H thin films were rf sputtered on various substrates, using a SiC target of constant composition. The experimental results showed that all films are amorphous with smooth surfaces, for the growth conditions used, and that the C/Si atomic ratio in the alloys is almost independent of substrate temperature. Infrared measurements showed that the hydrogen content in a-SiC:H films varied with Ts and increases with hydrogen flow rate increasing from 9 sccm to 20 sccm. Finally, the optical absorption coefficient was found to depend strongly on T s and hydrogen flow rate.
Active and Passive Electronic Components, 1993
In the present work a study of the electrical properties of heterojunctions between rf sputtered ... more In the present work a study of the electrical properties of heterojunctions between rf sputtered amorphous silicon carbide (a-SiC) thin films and n-type crystalline silicon (c-Si) substrates is reported. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics, as well as the temperature dependence of the current of a-SiC/c-Si(n) heterojunctions were measured. The I-V characteristics of a-SiC/ c-Si(n) heterojunctions exhibit poor rectification properties, with a high reverse current, at higher temperatures (T > 250K), whereas good rectification properties are obtained at lower temperatures (T < 250K). It was found that the a-SiC/c-Si(n) heterojunctions are isotype, suggesting that-the conductivity of a-SiC is n-type. The temperature dependence of the current (from 185K to 320K) showed that the majority carriers of c-Si(n) (i.e. electrons) are transported from c-Si(n) to a-SiC mainly by the thermionic emission mechanism, or by the drift-diffusion mechanism. From ...
4th International e-Conference on Studies in Humanities and Social Sciences: Conference Proceedings, 2019
Game takes place in school, in parks, in daycare places, early intervention programs, in therapeu... more Game takes place in school, in parks, in daycare places, early intervention programs, in therapeutic sessions and especially at home. It is an essential element of the development of all children and children with special needs. The use of game in the treatment and in the psychology of children with autism provides significant benefits for these children. Children with autism are extremely difficult to relate to others, especially to children of the same age in ordinary ways. Game is a wonderful tool that can help children with autism to participate in interactions. When it is used properly game can also allow children to discover their feelings, their environment, and their relationships with parents, siblings and children of the same age. Through play, children learn to communicate with others, express feelings, modify their behavior and develop problemsolving skills. They also learn various ways of building relationships with others. Game provides a safe psychological distance from their problems and allows them to express thoughts and emotions that are appropriate for their development.
Presentation experimentale et theorique de la modulation optique de la barriere de potentiel de c... more Presentation experimentale et theorique de la modulation optique de la barriere de potentiel de cette photodiode. On determine le transport des porteurs de charges de ce dispositif 3 couches (p+ n p) par la hauteur d'une barriere d'energie localisee dans le volume
IEEE Sensors Journal, 2019
Graphene oxide (GO) is a promising material for H 2 O vapour sensing. However, H 2 O sensing mech... more Graphene oxide (GO) is a promising material for H 2 O vapour sensing. However, H 2 O sensing mechanisms are still under investigation especially in the case of thermally reduced GO. To this purpose, planar devices were fabricated by spincoating graphene oxide on glass substrates. Ultra high response to H 2 O was recorded but poor repeatability and stability over time were also noted. Three different degrees of thermal reduction were applied to improve material stability. An inverse change of resistance was observed for reduced graphene oxide compared to pure graphene oxide upon interaction with H 2 O. The sensing mechanisms that govern GO and reduced GO behaviour were studied based on DC measurements. In the case of GO, strong ionic conductivity was proposed whereas in the case of reduced GO mixed electronic/ionic with the leading mechanism affected by H 2 O percentage in air, degree of material reduction and sensor working temperature. Finally, it was found that by promoting one sensing mechanism over the other, improved operating humidity range of the sensor can be achieved.
Applied Physics Letters, 2017
We demonstrate permanent water trapping in reduced graphene oxide (rGO) after high relative humid... more We demonstrate permanent water trapping in reduced graphene oxide (rGO) after high relative humidity (RH) exposure. For this purpose, we grew graphene oxide films via spin-coating on glass substrates followed by thermal reduction. The electrical resistance of the planar device was then measured. We observed that resistance is significantly increased after water vapor exposure and remains stable even after 250 days in ambient conditions. Various techniques were applied to desorb the water and decrease (recover) the material's resistance, but it was achieved only with low temperature thermal annealing (180 0 C) under forming gas (H 2 /N 2 mixture). The permanent effect of water absorption was also detected by x-ray photoelectron spectroscopy. Reduced graphene oxide (rGO) has attracted a strong research interest for gas sensing applications in recent years due to its unique electrical and chemical characteristics 1,2,3. Its main advantages among others are good chemical stability over time and ease of functionalization contributing to satisfying selectivity between various analytes 4. The gas sensing mechanism _____________________________
Thin Solid Films, 1995
Abstract The crystallization of a-Si films, grown by low-pressure chemical vapor deposition and a... more Abstract The crystallization of a-Si films, grown by low-pressure chemical vapor deposition and annealed by rapid thermal annealing (RTA), at 850 °C in conjunction with conventional heating at 600 °C for 6 h, has been studied using transmission electron microscopy. The results of RTA at 850 °C showed that the improvement of the poly-Si structure (large crystallites with low density of microtwins) was maximized for an annealing time of 150 s. The same results were also obtained by RTA at 850 °C with successive steps of 30 s duration each (5 × 30 s). A multiple-step annealing is sufficient to activate the movement of twin boundaries within the grains resulting in their annihilation. This process is compatible with the technology of growing good-quality poly-Si on low-cost glass substrates.
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Papers by Nikolaos Georgoulas