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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...

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.

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.

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 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.

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 ...

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 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 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 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.

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 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.

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 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...

A major amount of energy of mobile electrons and holes in a semiconductor under electric field are lost due to inter-carrier collisions prior to ionising collision. This fact causes a decrease in the ionisation probability which leads to the deterioration in ionisation rates especially when the doping density is high. The effects of this phenomenon on the high frequency and noise properties of highly doped impact avalanche transit time (IMPATT) devices based on different wide bandgap (WBG) semiconductors, like 4H-SiC, Wurtzite-GaN (Wz-GaN) and type-IIb diamond (C) have been studied in this paper. Significant deteriorations in the diodes' high frequency and noise performance have been observed in the simulation results. The simulation results have been compared with the experimental data in order to validate those.

A four-level 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 «- and p-epitaxial layers followed by the widths of those and the ratio of high to low doping concentrations have been varied subject to obtain the maximum large-signal DC to RF conversation 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 conversation 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 (NSVE) model developed by the authors is used for this purpose. The large-signal properties of the optimized DLHL Si IMPATT have been simulated and those are compared with the experimental results reported earlier. The said comparison shows that the optimized DLHL diode is capable of delivering significantly higher RF power output with greater DC to RF conversion efficiency at 60 GHz as compared to its un-optimized counterpart.

In this paper a novel method based on the concept of time varying depletion width modulation at large-signal levels is proposed to obtain the parasitic resistance of the inactive region of Ka-band Silicon Single-Drift Region (SDR) Impact Avalanche Transit Time (IMPATT) diodes. A complete simulation software based on non-sinusoidal voltage excitation method is developed to obtain the large-signal electric field snap-shots of the device at different bias current densities and different phase angles of a full cycle of steady-state oscillation from which the parasitic series resistance of the device is calculated. The series resistance is also calculated from the conventional method i.e., from the large-signal admittance characteristics at threshold frequency. The results however show that the proposed method to determine the series resistance provides better and closer agreement with the experimentally reported value than the conventional method.