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A Schottky barrier high-electron-mobility avalanche transit time (HEM-ATT) structure is proposed for terahertz (THz) wave generation. The structure is laterally oriented and based on AlGaN/GaN two-dimensional electron gas (2-DEG). Trenches are introduced at different positions of the top AlGaN barrier layer for realizing different sheet carrier density profiles at the 2-DEG channel; the resulting devices are equivalent to high–low, low–high and low-high–low quasi-Read structures. The DC, large-signal and noise simulations of the HEM-ATTs were carried out using the Silvaco ATLAS platform, non-sinusoidal-voltage-excited large-signal and double-iterative field-maximum small-signal simulation models, respectively. The breakdown voltages of the devices estimated via simulation were validated by using experimental measurements; they were found to be around 17–18 V. Under large-signal conditions, the series resistance of the device is estimated to be around 20 Ω. The large-signal simulation shows that the HEM-ATT source is capable of delivering nearly 300 mW of continuous-wave peak power with 11% conversion efficiency at 1.0 THz, which is a significant improvement over the achievable THz power output and efficiency from the conventional vertical GaN double-drift region (DDR) IMPATT THz source. The noise performance of the THz source was found to be significantly improved by using the quasi-Read HEM-ATT structures compared to the conventional vertical Schottky barrier IMPATT structure. These devices are compatible with the state-of-the-art medium-scale semiconductor device fabrication processes, with scope for further miniaturization, and may have significant potential for application in compact biomedical spectroscopy systems as THz solid-state sources.

Comprehensive experimental verification and theoretical analysis of a forced convection active cooling mechanism for an internet of things (IoT) based 360° video surveillance module have been prese...

Aims:: The potentiality of Multiple Quantum Well (MQW) Impacts Avalanche Transit Time (IMPATT) diodes based on Si~3C-SiC heterostructures as possible terahertz radiators have been explored in this paper. Objective:: The static, high frequency and noise performance of MQW devices operating at 94, 140, and 220 GHz atmospheric window frequencies, as well as 0.30 and 0.50 THz frequency bands, have been studied in this paper. Methods: The simulation methods based on a Self-Consistent Quantum Drift-Diffusion (SCQDD) model developed by the authors have been used for the above-mentioned studies. Results: Thus the noise performance of MQW DDRs will be obviously better as compared to the flat Si DDRs operating at different mm-wave and THz frequencies. Conclusion:: Simulation results show that Si~3C-SiC MQW IMPATT sources are capable of providing considerably higher RF power output with the significantly lower noise level at both millimeter-wave (mm-wave) and terahertz (THz) frequency bands as compared to conventional flat Si IMPATT sources.

A comparative study is done on Si, 4H-SiC, Wz-GaN and InP based impact avalanche transit time (IMPATT) diodes operating at 94 GHz. A double-iterative simulation procedure is utilized to investigate...

An analytical model has been developed by the authors for determining the angular alignment, position, length related parameters of a proposed real-time video surveillance system to be installed al...

This paper highlights the effect of temperature on the high-frequency performance of the double avalanche region avalanche transit time (ATT) source capable of operating in multiple numbers of freq...

In this paper, a junction-less charge plasma (CP) double-drift region (DDR) impact avalanche transit time (IMPATT) diode structure has been proposed for realizing a high-power and efficient terahertz (THz) source. A comprehensive two-dimensional (2-D) self-consistent quantum drift-diffusion (SCQDD) model has been developed by the author to study the static and THz performance of 4H-SiC based CP-DDR source designed to operate at 1.0 THz. Comparative studies on the DC and THz performance of the proposed device and conventionally doped vertical DDR IMPATT device reveal that the proposed CP-DDR can be the potential alternative of the conventional DDRs (C-DDRs), especially at the THz regime. The proposed THz CP-DDR source can be exclusively preferable over its conventional counterparts due to its easier and less complicated fabrication steps as well as equivalent performance capability with respect to the THz C-DDR sources.

A short review on avalanche transit time devices has been presented in this chapter. From its first proposal till the state of the art, impact avalanche transit time (IMPATT) sources for the generation of terahertz (THz) waves have been briefly described. The noise outputs of the sources at different electromagnetic spectrum have been discussed. The details of deferent device structures, potential materials, popular simulation techniques, etc. are also appended in this chapter.

Terahertz radiation has drawn enormous attention in recent times due to its various application possibilities. This chapter reviews various emerging trends and well-established technologies in Terahertz biomedical. Due to its extraordinary sensing capabilities, non-invasive, non-ionizing properties, sensitive instrumentations for spectroscopy and imaging, Terahertz has found various biomedical sensing applications from biomolecules, proteins to cells and tissues. This chapter highlights terahertz device engineering, system technologies, range of materials, aiming at various biomedical applications. It also includes emerging topics such as terahertz biomedical imaging, pattern recognition and tomographic reconstruction by machine learning and artificial intelligence, for possible biomedical imaging applications.

Great demand of suitable terahertz (THz) sources requires optimized design and appropriate simulation tool for designing and investigating the device capability at the design spectrum before actual fabrication. Design and simulation of complex devices like THz avalanche transit time (ATT) diodes require comprehensive and accurate simulation model for small-signal, large-signal and noise simulation before the actual fabrication. This chapter is devoted to summarize these three types of simulation methodologies for THz ATT sources.

In this preparatory chapter, a brief introduction to the generation, detection and processing of terahertz (THz) signals is given. Short descriptions of prospective applications of THz signals as well as some state-of-the-art electronic and photonic devices have also been included in this chapter. A chapter-wise overview of the entire book has been incorporated at the end of this introductory chapter.

An approximate model is presented in this chapter, which will be useful to study the static and dynamic performance of laterally oriented four-terminal single-drift (SD) IMPATT sources. This model is suitable for both sub-terahertz frequency and terahertz (THz) frequency of operation of the device. The details of the model are presented in this chapter; however, the simulation results are omitted from here due to the limitations in availability of space.

This chapter describes the procedure of estimating the degree of deterioration of the performance of avalanche transit time (ATT) sources due to instantaneous tunneling effect. The comparative study of Si, InP, GaAs and 4H-SiC ATT sources is presented. Tunneling-induced ATT phase delays in the oscillators are estimated and the degree of deterioration of the oscillators are interpreted via the estimated ATT phase delay at sub-terahertz frequency bands.

A high-power and low-noise 60 GHz impact avalanche transit time (IMPATT) source based on GaInAsP∼InP heterojunction has been proposed. The simulation experiments are done on InP based homojunction ...

An analytical model is developed for calculating the electric field-dependent electron ionization rate in bilayer graphene nanoribbons. All probable arrangements of optical phonon and inter-electron scattering phenomena before the occurrence of an ionizing collision event have been considered in this model, which is viewed as the multistage scattering model of impact ionization. This model considers both lucky ballistic and lucky drift electrons moving under an applied electric field. The numerical results calculated by using this model are compared with the results obtained from an earlier developed analytical model.

Background: The time and frequency responses of Multiple Quantum Barrier (MQB) nano-scale Avalanche Photodiodes (APDs) based on Si~3C-SiC material system have been investigated in this final part. Methods: A very narrow rectangular pulse of pulse-width of 0.4 ps has been used as the input optical pulse having 850 nm wavelength incidents on the p+-side of the MQB APD structures and corresponding current responses have been calculated by using a simulation method developed by the authors. Results: Finally the frequency responses of the devices are obtained via the Fourier transform of the corresponding pulse current responses in time domain. Conclusion: Simulation results show that MQB nano-APDs possess significantly faster time response and wider frequency response as compared to the flat Si nano-APDs under similar operating conditions.

Some exclusive material properties of gallium nitride (GaN) such as extraordinary transport, breakdown and thermal properties lead to highest combined frequency-power performance of GaN-based solid-state devices among all devices based on conventional semiconductors. Future needs of low-cost, compact and highly efficient terahertz (THz) systems are greatly endorsing the usage of GaN for realizing next-generation THz devices like quantum cascade lasers (QCLs), plasma THz heterostructure field-effect transistors (HFETs), negative differential resistance (NDR) diodes, GUNN diodes, impact avalanche transit time (IMPATT) diodes, high electron mobility transistors (HEMTs), antenna-coupled FETs, resonant-tunnelling diodes (RTDs), etc. This chapter deals with a comprehensive review of the above-mentioned GaN-based electronic and photonic devices since their inception to the state-of-the-art status of those; the chapter also discusses the impact of the recent developments of those devices on the future THz systems.

The mechanism of terahertz (THz) energy emission from gallium phosphide (GaP)-based avalanche transit time (ATT) sources has been discussed here. Six double-drift structured ATT devices based on GaP have been designed and optimized for operating at 0.1, 0.15, 0.2, 0.3, 0.5, and 1.0 THz frequencies. The large-signal results show that the THz performance of GaP ATT sources is more promising than the ATT oscillators based on conventional semiconductors.

The potentiality of graphene as a base substance of the terahertz (THz) sources has been explored in this chapter. The graphene can be used as the base substances of both active as well as passive THz radiators. In the passive THz radiator category, different graphene-based THz antennas have been discussed. On the other hand, graphene-based laser and avalanche transit time (ATT) THz sources have been reviewed under the active THz radiator category.

The fresh developments in the area of terahertz (THz) devices and systems based on gallium nitride (GaN) have lifted the requirement of the state-of-the-art noncontact characterization techniques. In this chapter, three major noncontact characterization techniques used for characterizing GaN-based THz devices have been described in details; those are (i) THz time-domain spectroscopy, (ii) laser-induced THz emission spectroscopy, and (iii) THz electromodulation spectroscopy. These noncontact characterization techniques have been established as potential alternatives of conventional contact measurement techniques due to their accuracy, reliability, and capability of providing noteworthy amount of visually interpretable information.

A brief introduction to different advanced materials for terahertz (THz) devices, circuits and systems has been included in this introductory chapter. The chapter also contains short discussions regarding potential applications of THz waves and different recently developed electronic and optoelectronic devices operating at THz spectrum. Finally, an overview of all the chapters included in this book has been provided at the end of this chapter.

A multi-stage-multi-iterative optimization (MSMIO) algorithm has been proposed in this paper for optimizing the design parameters of MQW DDR IMPATT diode based terahertz (THz) sources based on Al x Ga 1-x N~GaN heterostructures. The optimization has been carried out subject to achieve favourable large-signal (L-S) as well as avalanche noise characteristics of the source designed to operate at 1.0 THz. Six major parameters associated with the MQW structure, such as (i) mole fraction of Al in Al x Ga 1-x N, (ii) thickness of Al x Ga 1-x N layers, (iii) corresponding doping concentrations, (iv) thickness of GaN layers, (v) corresponding doping concentrations and (vi) bias current density are optimized subject to attain highest efficiency as well as lowest noise measure of the 1.0 THz source. The L-S and noise characteristics of optimized as well as un-optimized MQW DDR structures are compared in order to verify the proficiency of the algorithm; comparison is also done between simulation and experimental results of 1.0 THz oscillators based on other semiconductors reported earlier.

The impact ionization rate of electrons and holes in (0001)-oriented 4H-SiC has been measured under steady oblique magnetic field and hence, the influence of magnetic field on the breakdown characteristics of 4H-SiC diodes has been investigated. A set of three diodes having p+–n–n+ structure and another set of three diodes having n+–p–p+ structure have been grown on (0001)-oriented n+ and p+ 4H-SiC substrates using chemical vapor deposition (CVD) technique with different epitaxial layer thicknesses for carrying out the measurements within the electric field range of 2.5 × 108–4.0 × 108 V m−1. The ionization rate data are extracted from the photomultiplication measurements using ultra-violet light source of 260-nm wavelength. The ionization rates are found to be decreased with the increase of the magnetic field strength, especially at low electric fields; this decrement is found to be more pronounced in the ionization rate of electrons than the same of holes. A theoretical model developed by the authors is used to calculate the breakdown voltage of the 4H-SiC diodes. The numerical results are compared with the experimentally measured breakdown characteristics and those are found to be in good agreement within the externally applied magnetic field strengths of 0–1500 Gauss. Breakdown voltage of a diode is found to be increased due to the presence of magnetic field; the maximum values of these said increments are found to be around 5% and 2.6% in p+–n–n+ and n+–p–p+ diodes, respectively. Better magnetic field sensitivity is observed in the diodes having broader epitaxial layer widths.

Small-signal noise simulations have been performed to explore the potency of avalanche transit time (ATT) oscillators based upon wide bandgap (WBG) semiconducting substances like 3C-SiC and type-IIb diamond (C) as millimeter-wave (mm-wave) and terahertz (THz) wave generators; noise characteristics of those sources have been compared with the DDR IMPATTs on the basis of traditional substance, i.e., Si. The simulation studies show that the WBG semiconductor-based IMPATT sources possess significantly poor noise performance than the conventional Si-based IMPATT sources. However, significantly better RF power delivery capability of WBG IMPATT sources makes them superior than Si IMPATTs for mm-wave and THz applications.

The static and high-frequency simulations have been performed to explore the potency of avalanche transit time (ATT) oscillators based upon wide bandgap (WBG) semiconducting substances like 3C-SiC and type-IIb diamond (C) as millimeter-wave (mm-wave) and terahertz (THz) wave generators; characteristics of those sources have been compared with the DDR IMPATTs on the basis of traditional substance, i.e., Si. A non-sinusoidal voltage excited (NSVE) large-signal simulation procedure has been employed here to scrutinize the static and large-signal features of the sources. The simulation studies show that the DDR 3C-SiC IMPATTs possess better RF power delivery capability from 140 GHz to 1.0 THz as compared to the diamond IMPATTs, whereas the diamond IMPATT source is a better option for RF power generation at 94 GHz due to its better power generation capability at lower mm-wave frequencies. However, IMPATT sources based on both 3C-SiC and diamond are much powerful in comparison with mm-wave and THz IMPATT sources based on Si.

The degradation of high-frequency characteristics of a 1.0-THz double-drift region (DDR) impact avalanche transit time (IMPATT) diode based on wurtzite gallium nitride (Wz-GaN), due to the influence of parasitic series resistance, has been investigated. A two-dimensional (2-D) large-signal (L-S) simulation method based on a non-sinusoidal voltage excitation (NSVE) model has been used for this purpose. A comprehensive model of series resistance has been developed by considering the influence of skin effect, and the said model has been incorporated in the 2-D L-S simulation for studying the effect of RF power output and DC to RF conversion efficiency of the device. Results indicate 24.2–35.9% reduction in power output and efficiency due to the RF power dissipation in the positive series resistance. However, the device can still deliver 191.7–202.9 mW peak RF power to the load at 1.0 THz with 8.48–6.41% conversion efficiency. GaN IMPATT diodes are capable of generating higher RF power at around 1 THz than conventional diodes, but the effect of parasitic series resistance causes havoc reduction in power output and efficiency. The nature of the parasitic resistance is studied here in the level of device fabrication and optimization, which to our knowledge is not available at present.

An efficient piano note recognition scheme utilizing precise onset detection followed by segmented short-time Fourier transform (STFT) has been presented. The performance of the proposed scheme has been verified under different noise levels by adding additive white Gaussian noise (AWGN) of different power levels with the original music signal, i.e. by examining the proposed method under different signal-to-noise ratio (SNR).

The influence of inter-carrier scattering phenomena on the noise performance of double-drift region (DDR) impact avalanche transit time diodes has been investigated. Three optimized Si DDR ...

Objectives: This paper presents a noble system to detect vehicle thefts. If an unauthorized person tries to steal the vehicle, user and police station will be notified with GPS location. Methods: Fingerprints stored in the memory of the system. If the fingerprint and RFID matches with the stored ones then the controller triggers the powering circuit of the ECM else if the burglar tries to start the car in any other ways it sends the alert messages of the interventions as well as the car’s location to the owner’s mobile app via cloud. Findings: The system is implemented using Intel Galileo gen2 board. The GPS, GSM, Wi-Fi module as well as an SD Card is also connected to the board. Installing this smart system is helpful because this system won’t let the ECM to power on the engine as designed. The system also incorporates certain other sensors to stop the car burglary. If the burglar tries to turn on the battery by using paperclips in the fuses then the owner will be notified about the past proceedings along with GPS location of the car. Application: The system works well with low-price range car employed with keyless entry and self-start button and is unique because it uses IoT to protect the low price cars. Keywords: ECM, IoT, GPS, GSM, RFID

In this paper, an analytical model has been presented to study the influence of magnetic field on the impact ionization rate of charge carriers in semiconductors. The magnetic field is supposed to be applied along the oblique direction with respect to the direction of applied electric field. Numerical calculations have been carried out by using the comprehensive analytic expression of ionization rate of charge carriers formulated by the authors, in order to study the effect of oblique magnetic field on the ionization rate of electrons and holes moving under a steady electric field in 4H-SiC. Results show that the application of nonzero steady magnetic field in oblique direction leads to significant reduction in ionization rates. Moreover, the above-mentioned magnetic field-induced reduction in ionization rates is found to be maximum when the steady magnetic field is applied along the normal direction with respect to the external electric field.

Multiple quantum barriers have been used to suppress the dark current of nanoscale avalanche photodiodes (APDs). The n+–π–p+-structured Si–3C-SiC heterojunction-based multiple quantum barrier (MQB) APDs are considered and a detailed model of dark current has been developed from the self-consistent solution of the coupled Schrodinger–Poisson equations. Four major types of electron–hole pair (EHP) generation mechanisms such as (1) thermal generation, (2) band-to-band tunnelling generation, (3) trap-assisted tunnelling generation and (4) avalanche generation are considered for calculating variation of the total dark current with reverse bias voltage. It is observed that the dark current can be suppressed significantly by increasing both the number and thickness of quantum barriers. However, the authors have also admitted that both the number and thickness of quantum barriers cannot be increased indefinitely, since it will cause deterioration in spectral response of the device in near-infrared range (...

Корисність структури зі зворотною областю подвійного дрейфу (DDR) була вивчена для виготовлення IMPATT діода з нітриду галію (GaN), що працює на частоті 1,0 ТГц. Для перевірки можливостей структур з традиційною (нормальною) та зворотною DDR у терагерцовому діапазоні проведено моделювання статичних та великих сигналів. Виявлено, що функціонування GaN IMPATT діода можливе тільки у структурі зі зворотною DDR через більш низьке значення послідовного опору в порівнянні зі структурою з нормальною DDR. GaN IMPATT діод з нормальною DDR не може працювати у терагерцовому діапазоні. Однак раніше автори розрахували послідовний опір GaN IMPATT діода з традиційною DDR, призначеного для роботи на частоті 1,0 ТГц. Вони не враховували струм, що протікає, та опір розтіканню на омічних металевих контактах. Саме тому їх результати були помилковими. Отримані ними результати дозволяють зробити висновок, що GaN IMPATT діод з традиційною DDR у терагерцовому діапазоні може створювати достатній ефективний негативний опір, оскільки його послідовний опір залишається в діапазоні 1,5-2,0 Ом. У цій статті автори запропонували IMPATT структуру зі зворотною DDR виключно для матеріалу GaN і терагерцового діапазону частот. Використовуючи цю структуру зі зворотною DDR, p+-GaN ~ Ni/Au може отримати достатню площу контакту, так що опір анодного контакту буде мінімізовано. Розроблена авторами несинусоїдальна модель великого сигналу, що збуджується напругою, була використана для дослідження властивостей статичних (постійних) і великих сигналів структур з традиційною та зворотною DDR на частоті 1,0 ТГц. Це дослідження відкриває новий горизонт для вчених і дослідників у терагерцовому діапазоні. Utility of the reverse double-drift region (DDR) structure has been studied for fabricating the gallium nitride impact avalanche transit time (IMPATT) diode operating at 1.0 terahertz (THz). Static and largesignal simulations have been carried out in order to verify the THz capabilities of conventional (normal) and reverse DDR structures. It is revealed that IMPATT operation is only possible in a reverse GaN DDR structure due to the lower value of series resistance of it as compared to the normal GaN DDR structure. Normal DDR GaN IMPATT cannot be operational at THz regime. Earlier, the authors had calculated the series resistance of conventional GaN DDR IMPATT diode designed to operate at 1.0 THz, however. They did not take into account the current crowing and spreading resistance at the ohmic metal contacts. That is why, the results were misleading. Those results lead to the conclusion that conventional THz GaN DDR IMPATT may produce sufficient effective negative resistance since the series resistance of it remains within the range of 1.5-2.0 Ω. In this paper, authors have proposed a reverse DDR IMPATT structure exclusively for GaN material and THz frequency bands. By using this reverse DDR structure, p+-GaN ~ Ni/Au contact can obtain a sufficient contact area, so that the anode-contact resistance can be minimized. A nonsinusoidal voltage-excited large-signal model developed by the authors has been used to study the static (DC) and large-signal properties of conventional and reverse DDR structures at 1.0 THz. The present study on the evaluation of THz source seems to open a new horizon for THz researchers and scientists.

Two-dimensional large-signal and noise simulations are used to study the terahertz (THz) performance of Gallium Nitride (GaN) avalanche transit time source (ATT) source. A comprehensive model of parasitic series resistance has been developed by which the effect of series resistance on the large-signal and noise performance of the 1.0 THz GaN ATT source has been investigated; the proposed model is based on time varying depletion width modulation under large-signal oscillating condition. Significant amount of deterioration in power output and efficiency have been observed due to the existence of series resistance of the device. On the other hand, the realization of the optimized structure and doping profile as per the theoretical design is a tricky job by considering the state-of-the-art GaN fabrication technology. Especially, achieving the absolute values of epitaxial doping densities is almost an unrealistic task. Therefore, it is very important to acquire the knowledge about how much extent the power output, series resistance and noise measure of the source are affected due to the change in doping level of both n- and p-layers. In the present study, the sensitivities of the above-mentioned parameters with respect to the change in the doping densities of n- and p-layers have been investigated.

In this paper, the authors have presented a self-consistent quantum drift-diffusion model for multiple quantum well (MQW) impact avalanche transit time (IMPATT) diodes. The bound states in MQWs have been taken into account by self-consistent solutions of the coupled classical drift-diffusion (CLDD) equations and time-independent Schrodinger equations associated with both the conduction and valence bands. The static and high-frequency properties of MQW DDR IMPATTs based on Si$$\sim $$~3C-SiC material system designed to operate near 94-GHz atmospheric window have been studied by means of the above-mentioned self-consistent solutions of coupled CLDD equations and Schrodinger equations followed by a well-established double-iterative field maximum computational technique. A symmetric and two complementary asymmetric doping profiles for the proposed structures have been taken into account for the present study. The RF power outputs of Si$$\sim $$~3C-SiC MQW DDR IMPATTs near 94 GHz obtained from the simulation are compared with the experimentally obtained power outputs of flat DDR IMPATT diodes based on Si, GaAs, and InP at the same frequency band. It is observed that Si$$\sim $$~3C-SiC MQW DDR IMPATTs are capable of delivering significantly higher RF power compared with IMPATTs based on the above-mentioned materials especially when the doping concentrations of 3C-SiC layers are kept higher than those of the Si layers.