Graphene on different substrates, such as SiO2, h-BN and Al2O3, has been subjected to oscillatory electric fields to analyse the response of the carriers in order to explore the generation of ...terahertz radiation by means of high-order harmonic extraction. The properties of the ensemble Monte Carlo simulator employed for such study have allowed us to evaluate the high-order harmonic intensity and the spectral density of velocity fluctuations under different amplitudes of the periodic electric field, proving that strong field conditions are preferable for the established goal. Furthermore, by comparison of both harmonic intensity and noise level, the threshold bandwidth for harmonic extraction has been determined. The results have shown that graphene on h-BN presents the best featuring of the cases under analysis and that in comparison to III–V semiconductors, it is a very good option for high-order harmonic extraction under AC electric fields with large amplitudes.
The importance of interband transitions on the ultrafast relaxation process in photoexcited pristine graphene is evaluated by means of an ensemble Monte Carlo simulator. Impact ionization and Auger ...recombination in the collinear limit are considered, together with phonon-induced generation and recombination and intraband scattering mechanisms. The results show that collinear impact ionization is dominant in the first 100 femtoseconds, creating an important excess carrier population that is finally eliminated in the picosecond scale, together with the photoexcited population, by Auger and optical phonon-assisted recombination. The hot phonon effect is also important, stimulating phonon absorption and indirectly reducing the net collinear recombination in the hundreds of femtosecond range. The substrate type is an important factor, appeasing collinear impact ionization via screening and creating additional cooling channels that speed up the relaxation process. The results evidence that interband collinear generation processes are critical to explain the fastest stages of the relaxation process in graphene.
•Collinear impact ionization is of major importance in the first 100 fs.•Carrier multiplication is significant and lasts to the picosecond range.•Hot phonon effect appeases collinear recombination.•The substrate type is critical and provides additional cooling paths.
► Monte Carlo simulation of the RF and noise performance of Schottky barrier MOSFETs. ► The effective SB height affects the dynamic and noise figures of merit. ► Non-quasistatic parameters and ...microscopic transport improve with low SB height. ► Low SBs provide enhanced dynamic response while keeping excellent noise performance.
This paper presents a detailed study of the RF and noise performance of n-type Schottky barrier (SB) MOSFETs with a particular focus on the influence of the Schottky barrier height (SBH) on the main dynamic and noise figures of merit. With this aim, a 2D Monte Carlo simulator including tunnelling transport across Schottky interfaces has been developed, with special care to consider quantum transmission coefficients and the influence of image charge effects at the Schottky junctions. Particular attention is paid to the microscopic transport features, including carrier mean free paths or number of scattering events along the channel for investigating the optimization of the device topology and the strategic concepts related to the noise performance of this new architecture. A more effective control of the gate electrode over drain current for low SBH (discussed in terms of internal physical quantities) is translated into an enhanced transconductance gm, cut-off frequency fT, and non-quasistatic dynamic parameters. The drain and gate intrinsic noise sources show a noteworthy degradation with the SBH reduction due to the increased current, influence of hot carriers and reduced number of phonon scatterings. However, the results evidence that this effect is counterbalanced by the extremely improved dynamic performance in terms of gm and fT. Therefore, the deterioration of the intrinsic noise performance of the SB-MOSFET has no significant impact on high-frequency noise FoMs as NFmin, Rn and Gass for low SBH and large gate overdrive conditions. The role of the SBH on Γopt, optimum noise reactance and susceptance has been also analyzed.
In this paper, an ensemble Monte Carlo investigation of the static and dynamic performances in the high-frequency domain of laterally asymmetric channel (LAC) bulk metal-oxide-semiconductor ...field-effect transistors (MOSFETs) is presented. A detailed comparison with a homogeneously doped bulk device is also included. The results presented show that the use of an asymmetric doping within the channel enhances nonequilibrium features as velocity overshoot, thus significantly improving the transconductance of the device. The gradual variation of doping is also responsible for a modification of the electrostatic conditions and the inversion charge profiles, provoking the reduction of the gate-to-source capacitance, a minor influence of surface scattering, reduced transit times, and higher mean free paths. A noticeable enhancement (as compared to a conventional device) in the RF and microwave frequency range of the dynamic performance of the transistors is also evidenced. This is mainly due to a better transconductance-to-current ratio, Early voltage, and open-loop gain, which are the results of the improvement of the charge transport conditions in the device at a microscopic level. Therefore, LAC MOSFETs can be a viable option to enhance the figures of merit of bulk silicon technology for high-frequency analog applications.
In an educational context, multimedia content can be created by the students, by the faculty, or by a third party. With the aim of improving the lab work, motivation, and active learning in ...introductory electronics courses, several innovative technologies and instructional strategies were considered involving these three possibilities: real-time screen capture, video recording with smartphones, and technical analysis of science fiction films. Factors such as ease of use, fast production, or no need of expensive tools were critical for the choice of these technologies, which were introduced on activities (lab sessions, collaborative work) where traditional strategies required too much time or could not be applied properly due to a large number of students and/or time constraints. We found that video lab reports made by the students using smartphones are a very adequate and straightforward assessment method, combining the advantages of oral assessment and written reports. The technical analysis of science fiction films proved to be helpful to reinforce the motivation of some students towards the subject, although it requires some degree of maturity to reach this end. Video tutorials made with screen capture technology proved to be easy to record and produce, and they constitute a fast and convenient way to produce new multimedia resources adapted to the specific needs of the subject.
An exact solution of the quantum transmission coefficient has been obtained by using an Airy-transfer-matrix formalism to solve Schroumldinger equation. The procedure is applied to the calculation of ...the transmission coefficient in reverse-biased low Schottky diodes. The barrier profiles are given by Monte Carlo device simulations. As compared to the exact calculation, results indicate that injected current is much exacerbated when considering Wentzel-Kramers-Brillouin (WKB) approach or when neglecting quantum mechanical reflections for energies over the potential barrier. However, WKB could reasonably predict the total current if properly modifying the model parameters. Influence of barrier lowering is also discussed
This paper presents a series of activities and educational strategies related to the teaching of digital electronics in computer engineering. The main objective of these methodologies was to develop ...a final tutored coursework to be carried out by the students in small teams. This coursework was conceived as consisting of advanced problems or small projects that should serve as a compendium of the knowledge acquired during the course, with competition between the groups and students' assuming a professional role being key incentive factors. The result was that students had a high degree of motivation and engagement in the activity, as well as improved knowledge because of the self-learning required in carrying out the coursework.
In this paper, a detailed research of the high-frequency noise sources and figures of merit (FOMs) of fabricated deep-submicrometer n-channel fully depleted silicon-on-insulator MOSFETs is carried ...out. Special care is given to reproduce the main topology parameters, together with the most relevant parasitic elements of real devices in order to accomplish an accurate and reliable simulation. The information provided by the Monte Carlo (MC) tool allows getting a physical insight of the relationship between internal quantities and the main noise sources inside the device; moreover, the spectral density of velocity fluctuations has been analyzed spatially in order to determine the local current noise source in the gradual channel and velocity overshoot sections of the effective channel. Together with the calculation of intrinsic noise sources, the MC simulator is able to reproduce the measurements for the main noise FOMs in the RF and microwave frequency ranges. Moreover, the whole simulation framework allows addressing the importance of parasitic elements in the final value of these FOMs.
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