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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.

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...

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.

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...

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 ...

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.

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.

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.

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.

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 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 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.

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

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 (...

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.

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.

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.

The static, small-signal and noise characteristics of multiple quantum well (MQW) impact avalanche transit time (IMPATT) diodes operating at 94, 140, 220, 300 and 500 GHz frequencies have been investigated in this paper. The said MQW structures have been implemented by using Si~3C-SiC heterostructures. A self-consistent quantum drift-diffusion (SCQDD) model based simulation method has been used for the above mentioned studies. Simulation results show that Si~3C-SiC MQW IMPATT sources are highly proficient to provide considerably higher power output with significantly lower noise measure at aforementioned frequency bands as compared to conventional flat Si IMPATT sources.

The optoelectronic properties of $\text{Si}\sim 3\mathrm{C-SiC}$ hetero-junction based multiple quantum barrier (MQB) avalanche photodiodes (APDs) have been studied. The MQB APDs are found to be highly proficient devices for long wavelength detection. The number of quantum barriers (QBs) in MQB APDs has been varied and corresponding multiplication gain and excess noise factor (ENF) are calculated. Results indicate significantly reduced ENF of MQB devices as compared to the flat Si devices. It has also been clearly observed that reduction of ENF in MQB devices is directly related to the number of QBs. Current response of MQB APDs has been calculated for narrow rectangular shaped optical pulses of pulse-width of the order of picoseconds (ps) of wavelength 850 $\mu\mathrm{m}$ . Lastly, the time-domain current response has been Fourier transformed in order to obtain frequency response of the device. MQB APDs are found to be appreciably faster time and wider frequency responses than the flat Si APDs.

The dependence of static, high frequency and noise characteristics of Silicon based magnetic field tunable avalanche transit time (MAGTATT) sources operating at millimeter-wave atmospheric window frequencies (94, 140 and 220 GHz) and two different terahertz (THz) frequencies (0.3 and 0.5 THz) have been investigated in this paper. Comprehensive two-dimensional simulation models developed by the authors for evaluating static, large-signal and noise characteristics of MATATT diodes have been used for this purpose. The simulation results show that the above-mentioned magnetic field sensitivities are considerably reduced as the operating frequency increases.

In this paper, we study the effect of energy loss of charge carriers due to carrier-carrier interactions prior to impact ionization on the static and large-signal characteristics of double-drift region impact avalanche transit time (IMPATT) diodes based on Si designed to operate at millimeter-wave (mm-wave) atmospheric window frequencies such as 94, 140, and 220 GHz. The above mentioned effect has been incorporated in the simulation by taking into account a recently reported generalized analytical model of impact ionization rate of charge carriers based on multistage scattering phenomena in the base semiconductor. Results are compared with static and large-signal signal simulation results of the same diodes that we have reported earlier by taking into account the empirical relation of ionization rates fitted from the experimental data (experiment was carried out on IMPATT structures suitable for operating near 100 GHz). It is observed that both the large-signal RF power output and DC to RF conversion efficiency of the diodes are deteriorated significantly due to reduced ionization rates as a consequence of carrier-carrier collision events prior to the impact ionization. This effect is found to be more pronounced in 140 and 220 GHz diodes due to the enhanced carrier-carrier collisions within those diodes having greater background doping densities as compared to 94 GHz diode. The simulation results presented in this paper found to be in closer agreement with the experimental results as compared to the results that we have reported earlier.

This paper contains additional validations of a comprehensive analytical model based on multistage scattering phenomena to evaluate the impact ionization rates of charge carriers in semiconductors which was proposed by the authors and reported earlier. The model has been used to evaluate the ionization rates of both electrons and holes in some potential wide bandgap (WBG) semiconductors such as Wurtzite-GaN (Wz-GaN), type-IIb diamond and 6H-SiC. The numerical results obtained from the analytical model within the respective electric field ranges under consideration have been compared with the ionization rate values calculated by using the empirical relations fitted from the experimentally measured data. The calculated values of impact ionization rates of electrons and holes in all the WBG semiconductors under consideration are found to be in close agreement with the experimental results.

The authors have carried out the large-signal (L-S) simulation of double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on 111, 100, and 110 oriented GaAs. A nonsinusoidal voltage excited (NSVE) L-S simulation technique is used to investigate both the static and L-S performance of the above-mentioned devices designed to operate at millimeter-wave (mm-wave) atmospheric window frequencies, such as 35, 94, 140, and 220 GHz. Results show that 111 oriented GaAs diodes are capable of delivering maximum RF power with highest DC to RF conversion efficiency up to 94 GHz; however, the L-S performance of 110 oriented GaAs diodes exceeds their other counterparts while the frequency of operation increases above 94 GHz. The results presented in this paper will be helpful for the future experimentalists to choose the GaAs substrate of appropriate orientation to fabricate DDR GaAs IMPATT diodes at mm-wave frequencies.

The influence of self-heating on the millimeter-wave (mm-wave) and terahertz (THz) performance of double-drift region (DDR) impact avalanche transit time (IMPATT) sources based on silicon (Si) has been investigated in this paper. The dependences of static and large-signal parameters on junction temperature are estimated using a non-sinusoidal voltage excited (NSVE) large-signal simulation technique developed by the authors, which is based on the quantum-corrected drift-diffusion (QCDD) model. Linear variations of static parameters and non-linear variations of large-signal parameters with temperature have been observed. Analytical expressions representing the temperature dependences of static and large-signal parameters of the diodes are developed using linear and 2nd degree polynomial curve fitting techniques, which will be highly useful for optimizing the thermal design of the oscillators. Finally, the simulated results are found to be in close agreement with the experimentally measured data.

The important optoelectronic properties like spectral response, excess noise characteristics, time and frequency response of multiple quantum barrier (MQB) nano-scale avalanche photodiodes (APDs) based on Si~3C-SiC material system have been studied. A self-consistent simulation method based on quantum drift-diffusion model has been presented. Simulation results show that the Si~3C-SiC MQB nano-APDs are capable of detecting significantly longer wavelengths as compared to infrared flat Si APDs. The multiplication gain and excess noise factor (ENF) of the MQB APDs have been calculated by varying the number of quantum barriers (QBs). The numerically calculated ENF values of MQB APDs have been compared with the ENF of Si flat conventional APDs of similar dimensions and it is observed that the use of QBs leads to significant reduction in ENF of the APDs. Simulation results also show that MQB nano-APDs possess significantly faster time response and wider frequency response as compared to the Si counterparts.

The modulation of millimetre-wave (mm-wave) and terahertz (THz) properties of impact avalanche transit time (IMPATT) sources under external steady magnetic field has been studied in this paper. The arrangement of magnetic field tuning of IMPATT oscillators by using external transverse steady magnetic field is referred to as magnetic field tunable avalanche transit time (MAGTATT) oscillators. The sensitivities of various static, large-signal and noise characteristics of silicon-based MAGTATT sources operating at mm-wave atmospheric window frequencies (94, 140 and 220 GHz) and two different THz frequencies (0.3 and 0.5 THz) have been studied. Comprehensive two-dimensional simulation models developed by the authors for evaluating static, large-signal and noise characteristics of MATATT diodes have been used for this purpose. The simulation results show that the above-mentioned magnetic field sensitivities of the device properties are significantly reduced with the increase of the operating frequency.

The authors have developed a quantum corrected drift-diffusion model for impact avalanche transit time (IMPATT) devices by coupling the density gradient model with the classical drift-diffusion model. A large-signal simulation technique has been developed by incorporating the quantum potentials in the current density equations for the analysis of double-drift region IMPATT devices based on different semiconductors such as Wurtzite---GaN, InP, type-IIb diamond (C), 4H---SiC and Si deigned to operate at different millimeter-wave (mm-wave) and terahertz (THz) frequencies. It is observed that, the RF power output and DC to RF conversion efficiency of the devices operating at higher mm-wave ($$>$$>140 GHz) and THz frequencies reduce due to the incorporation of quantum corrections in the model; but the effect of quantum corrections are negligible for the devices operating at lower mm-wave frequencies ($$\le $$≤140 GHz).

In this paper, the influence of tunnelling on the RF performance of millimetre-wave (mm-wave) impact ionisation avalanche transit time (IMPATT) diodes operating in mixed tunnelling and avalanche transit time mode is studied by taking into account the parasitic series resistance of the device. The results show that the parasitic resistance of mm-wave IMPATTs increases and consequently the power delivered by the device decreases due to the consequence of band-to-band tunnelling. The critical background doping concentration and operating frequency are found to be 5.0 × 1023 m−3 and 260 GHz, respectively, above which the influence of tunnelling on the RF performance of the device becomes predominant.

A generalized analytical model based on multistage scattering phenomena has been developed in this paper for estimating the impact ionization rate of charge carriers in semiconductors. The probabilities of impact ionization initiated by electrons and holes have been calculated separately by taking into account all possible combinations of optical phonon scattering and carrier-carrier collisions prior to the impact ionization. Finally the analytical expressions of impact ionization rate of electrons and holes have been developed by using the aforementioned impact ionization probabilities. The impact ionization rates of electrons and holes in 4H-SiC have been calculated within the field range of $$2.5\times 10^{8}$$2.5×108---$$6.5\times 10^{8}\hbox { V m}^{-1}$$6.5×108Vm-1 by using the analytical expressions of those developed in the present paper. Those are also calculated by using the analytical expressions developed by some other researchers earlier without considering the multistage scattering phenomena. Finally the theoretical results obtained from the analytical model proposed in this paper and the analytical model developed by earlier researchers within the field range under consideration have been compared with the ionization rate values calculated by using the empirical relations fitted from the experimentally measured data. Closer agreement with the experimental data has been achieved when the impact ionization rate of charge carriers in 4H-SiC are calculated from the proposed model as compared to the earlier one.

A proposed four-step iterative optimization technique has been used to design a double low-high-low (DLHL) impact avalanche transit time (IMPATT) diode based on Si for 60 GHz operation. Initially the position of the charge bumps in both n- and p-epitaxial layers followed by the widths of those and the ratio of high to low doping concentrations have been varied to obtain the maximum large-signal DC to radio frequency (RF) conversion efficiency from the device. Finally the bias current density is varied within a specified range to obtain the optimum value of it for which the DC to RF conversion efficiency of the device is maximum. The above-mentioned four optimization steps have been repeated until the method converges to provide a stable optimized DC to RF conversion efficiency. A large-signal simulation technique based on non-sinusoidal voltage excitation model developed by the authors is used for this purpose. The large-signal properties of the optimized DLHL Si IMPATT have been simulated and tho...

The potentialities of double-drift region (DDR) impact avalanche transit time (IMPATT) devices based on group III–V semiconductor material Wurtzite-gallium nitride (Wz-GaN) as possible millimetre-wave (mm-wave) and terahertz (THz) sources have been explored in this paper. A large-signal (L-S) simulation technique based on a non-sinusoidal voltage excitation model (NVSE) developed by the authors has been used to study the high-frequency properties of DDR Wz-GaN IMPATTs at both mm-wave and THz frequencies. Similar studies have also been carried out for DDR IMPATTs based on some other conventional semiconductor materials such as GaAs (group III–V), InP (group III–V) and Si (group IV). Results show that DDR Wz-GaN IMPATTs excel all other devices under consideration as regards radio-frequency performance at both mm-wave and THz frequencies.

The authors have proposed a complete large-signal (L-S) model to investigate the optical modulation of high frequency properties of double-drift region (DDR) impact avalanche transit time (IMPATT) devices operating at different millimeter-wave and sub-millimeter-wave frequencies. Simulation is carried out based on the proposed model to study the effect of photo-irradiation of different values of incident optical power of different wavelengths from 600---1000 nm on the DC and L-S characteristics of DDR IMPATTs based on Si designed to operate at 94, 140, 220, 300 and 500 GHz. Two different optical illumination configurations such as top mount and flip chip are taken into account for the present study. Results show that the maximum optical tuning of L-S parameters of the device can be achieved for optical illumination of wavelength 700 nm, i.e. near the wavelength corresponding to the responsivity peak of Si in both top mount and flip chip configurations. Further, better photo-sensitivity of top mount structure is observed as compared to its flip chip counterpart. The simulation results are found to be in good agreement with the experimental results reported earlier. Suitable tunable light source information is also suggested to carry out the optical control experiment within the wavelength range under consideration.

In this paper, the authors have made an attempt to study the effect of photo-irradiation on the avalanche noise properties of double-drift region (DDR) mixed tunnelling and avalanche transit time (MITATT) device. A model to analyse the avalanche noise of illuminated DDR MITATT devices under small-signal condition is proposed and simulation is carried out to study the noise properties of the device based on silicon designed to operate at W-band. The results show that avalanche noise measure of the device under two different optical illumination configurations such as Flip Chip (FC) and Top Mount (TM) are 37.1 dB and 40.2 dB, respectively, for the incident photon flux density of 1026 m−2 sec−1 at 1000 nm wavelength while the noise measure of the same device under dark condition is 35 dB. Thus, the increase of avalanche noise due to the incident photon flux on optically illuminated device can be reduced if FC configuration is taken instead of TM configuration.

An attempt is made in this paper to study the influence of skin depth on the parasitic series resistance of millimeter-wave IMPATT devices based on Silicon. The method is based on the concept of depletion width modulation of the device under large-signal condition. A large-signal simulation model based on non-sinusoidal voltage excitation is used for this study. The electric field snap-shots of 35 GHz Single-Drift Region (SDR) and 94 GHz Double-Drift Region (DDR) IMPATT devices are first obtained from which the series resistances are estimated by incorporating the effect of skin depth in the modeling and simulation. The series resistances of these devices are also obtained by neglecting the effect of skin depth. The values of series resistances obtained from the simulation are compared with the corresponding experimentally reported values. It is observed that the series resistance estimated by including the skin effect is in closer agreement with the experimental values as compared to that without including the same. Thus the skin effect plays an important role for determining the series resistance of IMPATT devices at millimeter-wave frequency bands.

Large-signal (L-S) characterization of double-drift region (DDR) impact avalanche transit time (IMPATT) devices based on silicon designed to operate at different millimeter-wave (mm-wave) and terahertz (THz) frequencies up to 0.5 THz is carried out in this paper using an L-S simulation method developed by the authors based on non-sinusoidal voltage excitation (NSVE) model. L-S simulation results show that the device is capable of delivering peak RF power of 657.64 mW with 8.25% conversion efficiency at 94 GHz for 50% voltage modulation; whereas RF power output and efficiency reduce to 89.61 mW and 2.22% respectively at 0.5 THz for same voltage modulation. Effect of parasitic series resistance on the L-S properties of DDR Si IMPATTs is also investigated, which shows that the decrease in RF power output and conversion efficiency of the device due to series resistance is more pronounced at higher frequencies especially at the THz regime. The NSVE L-S simulation results are compared with well established double-iterative field maximum (DEFM) small-signal (S-S) simulation results and finally both are compared with the experimental results. The comparative study shows that the proposed NSVE L-S simulation results are in closer agreement with experimental results as compared to those of DEFM S-S simulation.

The avalanche noise performance of multiple quantum well (MQW) DDR IMPATT devices has been investigated. A self-consistent quantum drift-diffusion (SCDD) model is used for the simulation study. The noise performance of one Si based flat and two Si∼3C-SiC MQW DDRs have been studied in this paper. Results indicate that considerable low noise operation with high power output can be obtained at W-band by using the Si∼3C-SiC MQW DDR structures.

The effect of energy-loss due to electron-electron (e-e) and hole-hole (h-h) collisions on the avalanche noise performance of IMPATT diodes has been studied. Simulations have been carried out on DDR Si IMPATTs operating at 94, 140 and 220 GHz. Simulation results show that the noise measure of the diodes considerably increases due to e-e and h-h interactions within the space charge layer of the device. This is observed to be more influential at higher mm-wave frequencies.

The authors have made an attempt to investigate the effect of electron versus hole photocurrent on the optoelectric properties of p+-p-n-n+ structured Wurtzite-GaN (Wz-GaN) reach-through avalanche photodiodes (RAPDs). The photo responsivity and optical gain of the devices are obtained within the wavelength range of 300 to 450 nm using a novel modeling and simulation technique developed by the authors. Two optical illumination configurations of the device such as Top Mounted (TM) and Flip Chip (FC) are considered for the present study to investigate the optoelectric performance of the device separately due to electron dominated and hole dominated photocurrents, respectively, in the visible-blind ultraviolet (UV) spectrum. The results show that the peak unity gain responsivity and corresponding optical gain of the device are 555.78 mA W−1 and 9.4144×103, respectively, due to hole dominated photocurrent (i.e., in FC structure); while those are 480.56 mA W−1 and 7.8800×103, respectively, due to electron dominated photocurrent (i.e., in TM structure) at the wavelength of 365 nm and for applied reverse bias of 85 V. Thus, better optoelectric performance of Wz-GaN RAPDs can be achieved when the photocurrent is made hole dominated by allowing the UV light to be shined on the n+-layer instead of p+-layer of the device.

Influences of magnetic field on the noise performance of double-drift region (DDR) impact avalanche transit time (IMPATT) device based on Si designed to operate within W-band (75–110 GHz) have been studied in this paper. The reverse biased DDR IMPATT structure under transverse magnetic field can be regarded as magnetic field tunable avalanche transit time (MAGTATT) device. The simulation results show that both the noise spectral density and noise measure of the device increase significantly while the device is kept in transverse magnetic field. This degradation of the noise performance of the device enhances when the magnitude of the magnetic field is increased. Therefore, in order to achieve the magnetic field tuning of the RF properties of DDR IMPATTs as reported earlier by the authors, the noise performance of the source has to be sacrificed in fair extent.