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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.

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.

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.

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.

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.

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.

The effect of magnetic field on the noise performance of the magnetic field tunable avalanche transit time (MAGTATT) device based on Si, designed to operate at W-band (75 – 110 GHz), has been studied in this paper. A comprehensive two-dimensional (2D) model has been developed. The simulation results show that due to the presence of applied external transverse magnetic field, both the noise spectral density and noise measure of the MAGTATT device increase significantly. The noise performance of the device has been found to be further deteriorated if the magnetic field strength is further increased. Hence, in order to achieve the magnetic field tuning of the radio frequency (RF) properties of impact avalanche transit time (IMPATT) source, the noise performance of it has to be sacrificed in fair extent. Moreover, it clearly indicates that an IMPATT source must be covered with appropriate magnetic shielding material to avoid undesirable shift in operating frequency and output power and objectionable amount of deterioration in noise performance due to the presence of external magnetic field.

In this paper, a two-dimensional (2-D) large-signal model has been presented to study the effect of steady magnetic field on the RF performance of millimeter-wave (mm-wave) double-drift region impact avalanche transit time device. Magnetic field sensitivities of various static and large-signal parameters of the device designed to operate at W-band have been calculated and discussed in detail. Results show that the frequency tuning of the source of around 3.64 GHz is achievable with maximum sensitivity of about $$-$$-1.59 GHz $$\hbox {T}^{-1}$$T-1 for the application of transverse magnetic field varying from 4.0 to 5.0 T. The nature of both frequency and power tuning of the device due to application of transverse magnetic field is in good agreement with the experimental results carried out 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 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 quantum mechanical behavior of a reverse biased nano-scale $$p$$p-$$n$$n junction based on $$\hbox {Si/Si}_{0.4}\hbox {Ge}_{0.6}/\hbox {Si}$$Si/Si0.4Ge0.6/Si quantum well has been studied by obtaining the self-consistent solution of coupled Schrodinger and Poisson equations. The carrier confinement within the said quantum well structure has been investigated by analyzing the special variations of electron and hole densities throughout the device structure obtained from the self-consistent solution of coupled Schrodinger and Poisson equations for different widths of the quantum well. The tunnel current across the junction has also been calculated for the heterostructure for different applied reverse bias voltages. Results show that, due to the greater depth of the quantum well in conduction band as compared to that in valance band of $$\hbox {Si/Si}_{0.4}\hbox {Ge}_{0.6}/\hbox {Si}$$Si/Si0.4Ge0.6/Si heterostructure, the quantum confinement effect is more pronounced for electrons in conduction band as compared to that for holes in valance band. Finally the current-voltage characteristics of the heterostructure under consideration have been investigated for different widths of the quantum well. It is observed that the modulation of tunnel current may be achieved by varying the width of the quantum well. The present study is the groundwork for investigating the optoelectronic properties of nano-scale photodetectors based on $$\hbox {Si/Si}_{1-x}\hbox {Ge}_{x}/\hbox {Si}$$Si/Si1-xGex/Si material system capable of detecting longer wavelengths around 1.30 and 1.55 $$\upmu \hbox {m}$$μm.

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.

Quantum correction is necessary on the classical drift-diffusion (CLDD) model to predict the accurate behavior of high frequency performance of ATT devices at frequencies greater than 200 GHz when the active layer of the device shrinks in the range of 150---350 nm. In the present work, a quantum drift-diffusion model for impact avalanche transit time (IMPATT) devices has been developed by incorporating appropriate quantum mechanical corrections based on density-gradient theory which macroscopically takes into account important quantum mechanical effects such as quantum confinement, quantum tunneling, etc. into the CLDD model. Quantum potentials (synonymous as Bohm potentials) have been incorporated in the current density equations as necessary quantum mechanical corrections for the analysis of millimeter-wave (mm-wave) and Terahertz (THz) IMPATT devices. It is observed that the large-signal (L-S) performance of the device is degraded due to the incorporation of quantum corrections into the model when the frequency of operation increases above 200 GHz; while the effect of quantum corrections are negligible for the devices operating at lower mm-wave 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.

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 simulation is carried out in this paper to investigate the prospects and potentiality of Double-Drift Region (DDR) Impact Avalanche Transit Time (IMPATT) device based on semiconducting type-IIb diamond as millimeter-wave source operating at 94 GHz atmospheric window frequency. Large-signal simulation method developed by the authors and presented in this paper is based on non-sinusoidal voltage excitation. The simulation is carried out to obtain the large-signal characteristics such as RF power output, DC to RF conversion efficiency etc. of DDR diamond IMPATT device designed to operate at 94 GHz. The results show that the device is capable of delivering a peak RF power output of 7.01 W with 10.18% DC to RF conversion efficiency for a bias current density of 6.0×10^8 A m^-2 and voltage modulation of 60% at 94 GHz; whereas for the same voltage modulation 94 GHz DDR Si IMPATT can deliver only 693.82 mW RF power with 8.74 efficiency for the bias current density of 3.4×10^8 A m^-2.

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.

In this paper large-signal modeling and simulation has been carried to study the frequency chirping due to temperature transients and the large-signal power and efficiency of pulsed silicon Double-Drift Region (DDR) Impact Avalanche Transit Time (IMPATT) device operating at 94 GHz. A large-signal simulation method based on non-sinusoidal voltage excitation incorporating the transient thermal effect has been developed by the authors. Results show that the device is capable of delivering a peak pulsed power output of 17.5 W with 12.8% efficiency when the voltage modulation is 60%. The maximum junction temperature rise is 350.2 K for a peak pulsed bias current of 6.79 A with 100 ns pulsewidth and 0.5 percent duty cycle; whereas the chirp bandwidth is 8.3 GHz.

The effect of photon flux density on the noise properties of optically illuminated Double Drift Region (DDR) Mixed Tunneling Avalanche Transit Time (MITATT) device is investigated in this paper. An analytical model is proposed to obtain a relationship between the normalized difference of electron and hole current density of DDR device and the incident photon flux on it. Simulation is carried out to study the small signal noise spectral density and noise measure of the device under optical illumination. Two illumination configurations i.e., Flip Chip (FC) and Top Mounted (TM) structures are considered in the simulation. The device is designed to operate at mm-wave window frequency at W-band. The results show that avalanche noise measures of FC and TM structures of photo irradiated device are 37.1 dB and 40.2 dB respectively for an incident photon flux density of 1024 m-2 sec-1 at 1000 nm wavelength near band gap absorption of Silicon. The noise measure of the un-illuminated device is found to be 35 dB. The results indicate that the increase of avalanche noise due to the incident photon flux can be reduced if FC structure is taken instead of TM structure.

The effect of optical illumination on DC and dynamic performance of Si1-xGex based double drift region (DDR) (p+pnn+) IMPATT diode operating at W-Band is investigated and compared with its Silicon counterpart. Top Mounted (TM) and Flip Chip (FC) structures are chosen and the composition of photocurrent is altered by shining light on the p+ side and n+ side of the device through optical windows. A double iterative computer simulation method based on drift-diffusion model has been used to study the small signal performance and subsequent modification of the small signal parameters owing to optical illumination. The role of leakage current in controlling the dynamic properties is studied by varying the current multiplication factors for electrons (Mn) and for holes (Mp). It is observed that both the DC and small signal parameters of both the diodes are affected significantly due to optical illumination. Under optical illumination of the device, the frequency shift is observed to be more upwards upon lowering of Mn than lowering of Mp for both the diodes. The frequency chirping in both Si1-xGex and Si IMPATTs are found to be of the order of few GHz, thereby indicating their high photo-sensitiveness at W-Band. But the results significantly indicates that photo-sensitiveness of Si1-xGex IMPATT is much greater than the Si IMPATT which is one of the major findings of this work.

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.

Noise performance of different structures of anisotype heterojunction double-drift region (DDR) mixed tunneling and avalanche transit time (MITATT) devices has been studied. The devices are designed for operation at millimeter-wave W-band frequencies. A simulation model has been developed to study the noise spectral density and noise measure of the device. Two different mole fractions and of Ge and corresponding four types of device structure are considered for the simulation. The results show that the -Si heterojunction DDR structure of MITATT device excels all other structures as regards noise spectral density ( sec) and noise measure (33.09 dB) as well as millimeter-wave properties such as DC-to-RF conversion efficiency (20.15%) and CW power output (773.29 mW).

A generalized method for small-signal simulation of avalanche noise in Mixed Tunneling Avalanche Transit Time (MITATT) device is presented in this paper where the effect of series resistance is taken into account. The method is applied to a millimeter-wave Double Drift Region (DDR) MITATT device based on Silicon to obtain noise spectral density and noise measure as a function of frequency for different values of series resistance. It is found that noise measure of the device at the operating frequency (122 GHz) with input power density of 1010 Watt/m2 is about 35 dB for hypothetical parasitic series resistance of zero ohm (estimated junction temperature = 500 K). Results show that the noise measure increases as the value of parasitic resistance increases., {"references":["T. A. Midford and R. L. Bernick, \"Millimeter Wave CW IMPATT\ndiodes and Oscillators\", IEEE Trans. Microwave Theory Tech., vol. 27,\npp. 483-492, 1979.","Y. Chang, J. M. Hellum, J. A. Paul and K. P. 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In this paper the potentiality of impact avalanche transit time (IMPATT) devices based on different semiconductor materials such as GaAs, Si, InP, 4H-SiC and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz frequencies. Drift–diffusion model is used to design double-drift region (DDR) IMPATTs based on different materials at millimeter-wave (mm-wave) and terahertz (THz) frequencies. The performance limitations of these devices are studied from the avalanche response times at different mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of GaAs and Si DDR IMPATTs are 220 GHz and 0.5 THz, respectively, whereas the same for InP and 4H-SiC DDR IMPATTs is 1.0 THz. Wz-GaN DDR IMPATTs are found to be excellent candidate for generation of RF power at THz frequencies of the order of 5.0 THz with appreciable DC to RF conversion efficiency. Further, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs as regards their RF power outputs. Thus, the wide bandgap semiconductors such as Wz-GaN and 4H-SiC are highly suitable materials for DDR IMPATTs at both mm-wave and THz frequency ranges.