Impact Avalanche Transit Time Devices Research Articles

Optimal Design of Large Signal Performance of AlN/GaN Hetero-Structural IMPATT and MITATT Diodes

Hetero-structure of AlxGa1-xN/GaN exhibits important applications in high frequency and large power devices. In this paper, AlN/GaN is adopted to optimal design the large power impact avalanche transit time (IMPATT) and mixed tunneling avalanche transit time (MITATT) diodes operating at the atmospheric low loss window frequency of 0.85 THz. The static state and large signal characteristics of the devices are numerically simulated. The values of peak electric field strength, break-down voltage, avalanche voltage, the maximum generation rates of avalanche and tunneling, admittance-frequency relation, output power, conversion efficiency, quality factor of the proposed hetero-structural IMPATT and MITATT diodes are calculated, respectively. Via comparing the obtained results of (n)AlN/(p)GaN and (n)GaN/(p)AlN IMPATT diodes to those of the MITATT counterparts, there exists little performance difference between IMPATT and MITATT devices while implies significant difference between the (n)AlN/(p)GaN and (n)GaN/(p)AlN diodes.

Simulation on Large Signal and Noise Properties of (n)Si/(p)SiC Heterostructural IMPATT Diodes

Si/SiC heterostructural impact avalanche transit time (IMPATT) diode indicates of important applications in Terahertz (THz) power source, integrated circuit etc. In this paper, the (n)Si/(p)4H-SiC, (n)Si/(p)6H-SiC, (n)Si/(p)3C-SiC heterostructural double drift region IMPATT diodes operating at the atmospheric window frequency of 0.85 THz are designed by the drift-diffusion model while their static state, large signal and noise properties are numerically simulated. The performance parameters of the studied devices such as breakdown voltage, peak electric field strength, optimal negative conductance, output power, power conversion efficiency, admittance-frequency relation, quality factor, noise electric field, mean-square noise voltage per band-width and noise measure were calculated and compared. This method can guide for optimizing the Si/SiC heterostructural IMPATT device in the future.

Effect of magnetic field on the RF performance of millimeter-wave IMPATT source

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.

Heterojunction DDR THz IMPATT diodes based on AlxGa1−xN/GaN material system

Simulation studies are made on the large-signal RF performance and avalanche noise properties of heterojunction double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on AlxGa1−xN/GaN material system designed to operate at 1.0 THz frequency. Two different heterojunction DDR structures such as n-Al0.4Ga0.6N/p-GaN and n-GaN/p-Al0.4Ga0.6N are proposed in this study. The large-signal output power, conversion efficiency and noise properties of the heterojunction DDR IMPATTs are compared with homojunction DDR IMPATT devices based on GaN and Al0.4Ga0.6N. The results show that the n-Al0.4Ga0.6N/p-GaN heterojunction DDR device not only surpasses the n-GaN/p-Al0.4Ga0.6N DDR device but also homojunction DDR IMPATTs based on GaN and Al0.4Ga0.6N as regards large-signal conversion efficiency, power output and avalanche noise performance at 1.0 THz.

Quantum corrected drift-diffusion model for terahertz IMPATTs based on different semiconductors

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).

Large-signal characterizations of DDR IMPATT devices based on group III–V semiconductors at millimeter-wave and terahertz frequencies

Large-signal (L-S) characterizations of double-drift region (DDR) impact avalanche transit time (IMPATT) devices based on group III–V semiconductors such as wurtzite (Wz) GaN, GaAs and InP have been carried out at both millimeter-wave (mm-wave) and terahertz (THz) frequency bands. A L-S simulation technique based on a non-sinusoidal voltage excitation (NSVE) model developed by the authors has been used to obtain the high frequency properties of the above mentioned devices. The effect of band-to-band tunneling on the L-S properties of the device at different mm-wave and THz frequencies are also investigated. Similar studies are also carried out for DDR IMPATTs based on the most popular semiconductor material, i.e. Si, for the sake of comparison. A comparative study of the devices based on conventional semiconductor materials (i.e. GaAs, InP and Si) with those based on Wz-GaN shows significantly better performance capabilities of the latter at both mm-wave and THz frequencies.

Quantum drift-diffusion model for IMPATT devices

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.

IMPATT devices based on group III–V compound semiconductors: prospects as potential terahertz radiators

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.

Potentiality of semiconducting diamond as the base material of millimeter-wave and terahertz IMPATT devices

An attempt is made in this paper to explore the potentiality of semiconducting type-IIb diamond as the base material of double-drift region (DDR) impact avalanche transit time (IMPATT) devices operating at both millimetre-wave (mm-wave) and terahertz (THz) frequencies. A rigorous large-signal (L-S) simulation based on the non-sinusoidal voltage excitation (NSVE) model developed earlier by the authors is used in this study. At first, a simulation study based on avalanche response time reveals that the upper cut-off frequency for DDR diamond IMPATTs is 1.5 THz, while the same for conventional DDR Si IMPATTs is much smaller, i.e. 0.5 THz. The L-S simulation results show that the DDR diamond IMPATT device delivers a peak RF power of 7.79 W with an 18.17% conversion efficiency at 94 GHz; while at 1.5 THz, the peak power output and conversion efficiency decrease to 6.19 mW and 8.17% respectively, taking 50% voltage modulation. A comparative study of DDR IMPATTs based on diamond and Si shows that the former excels over the later as regards high frequency and high power performance at both mm-wave and THz frequency bands. The effect of band to band tunneling on the L-S properties of DDR diamond and Si IMPATTs has also been studied at different mm-wave and THz frequencies.

Potentiality of IMPATT Devices as Terahertz Source: An Avalanche Response Time-based Approach to Determine the Upper Cut-off Frequency Limits

Potentiality of Impact Avalanche Transit Time (IMPATT) devices based on different semiconductor materials such as InP, 4H-SiC, and Wurtzite-GaN (Wz-GaN) has been explored for operation at terahertz (THz) frequencies. Drift-diffusion model is used to design double-drift region (DDR) IMPATTs based on above mentioned materials at different millimeter-wave (mm-wave) and THz frequencies and the upper cut-off frequency limits of those devices are obtained from the avalanche response times at those mm-wave and THz frequencies. Results show that the upper cut-off frequency limits of both InP and 4H-SiC DDR IMPATTs are 1.0 THz; whereas, the same is 5.0 THz in Wz-GaN DDR IMPATTs. The Wz-GaN DDR IMPATTs emerge as the most suitable devices for generation of THz frequencies due to their small avalanche response time, high DC to RF conversion ratio, and sufficiently high RF power output at THz frequencies. But, it is observed that up to 1.0 THz, 4H-SiC DDR IMPATTs excel Wz-GaN DDR IMPATTs due to their higher output power densities. 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.

Effect of junction temperature on the large-signal properties of a 94 GHz silicon based double-drift region impact avalanche transit time device

The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave (CW) and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson's method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.

A proposed simulation technique to study the series resistance and related millimeter-wave properties of Ka-band Si IMPATTs from the electric field snapshots

A large-signal model and a simulation technique based on non-sinusoidal voltage excitation are used to obtain the electric field snapshots from which the series resistance and related high-frequency properties of a 35 GHz Silicon Single-Drift Region (SDR) Impact Avalanche Transit Time (IMPATT) device have been estimated for different bias current densities. A novel method is proposed in this paper to determine the parasitic series resistance of a millimeter-wave IMPATT device from large-signal electric field snapshots at different phase angles of a full cycle of steady-state oscillation. The method is based on the depletion width modulation of the device under a large-signal condition. The series resistance of the device is also obtained from the large-signal admittance characteristics at threshold frequency. The values of series resistance of a 35 GHz SDR IMPATT diode obtained from the proposed method and the large-signal admittance method are compared with experimentally reported values. The results show that the proposed method provides better and closer agreement with the experimental value.

Prospects of IMPATT devices based on wide bandgap semiconductors as potential terahertz sources

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.

GaN based transfer electron and avalanche transit time devices

A new model is developed to study the microwave/mm wave characteristics of two-terminal GaN-based transfer electron devices (TEDs), namely a Gunn diode and an impact avalanche transit time (IMPATT) device. Microwave characteristics such as device efficiency and the microwave power generated are computed and compared at D-band (140 GHz center frequency) to see the potentiality of each device under the same operating conditions. It is seen that GaN-based IMPATT devices surpass the Gunn diode in the said frequency region.

Comparative study on the high-bandgap material (GaN and SiC)-based impact avalanche transit time device

The dynamic characteristics of GaN and SiC-based impact avalanche transit times (IMPATTs) are reported at D-band. The device properties are compared at the same operating conditions and frequency of operations. A noise analysis model is employed to assess the performance studies. The noise of SiC-based IMPATTs is found to be higher than that of GaN-based IMPATTs. It is shown that the high-bandgap semiconductor material-based IMPATTs are potential candidates for replacing traditional IMPATTs at high frequency of operation. The computed power densities are found to be, respectively, 2.48times10 7 , 2.78times10 7 and 0.07times10 7 W/cm 2 for SiC, GaN and GaAs-based IMPATTs at the same operating conditions.

Photosensitivity Analysis of Gallium Nitride and Silicon Carbide Terahertz IMPATT Oscillators: Comparison of Theoretical Reliability and Study on Experimental Feasibility

Reliability of terahertz-frequency (~1.0 THz) characteristics of wide-bandgap (WBG) wurtzite (Wz)-GaN- and 4H-SiC-based p++nn++-type single-drift-region (SDR) impact avalanche transit time (IMPATT) devices (normal and photoilluminated) is compared through a simulation scheme. The simulation experiment reveals that an RF power density of 3.37 times 1011 W middotm-2 (efficiency of 18.2%) at around 1.126 THz may be realized from the optimized unilluminated GaN IMPATT device, whereas the unilluminated 4H-SiC IMPATT device is expected to generate an RF power density of 1.35 times 1011 W middotm-2 (efficiency of 9%) at 1.05 THz. However, the parasitic series resistance reduces the maximum exploitable power density from the terahertz devices. Under optical illumination, additional photogenerated carriers are created in the devices, and these carriers change the admittance and negative resistance properties of the terahertz IMPATT diodes. The performance modulation of the terahertz devices is simulated, and the results are compared in this paper. Under external radiation, the operating frequencies of the GaN- and SiC-based diodes are found to shift upward by 6.0 and 40.0 GHz, respectively, with degradation of maximum output-power density level and device negative resistance. The extensive simulation experiments establish that, although the photosensitivity of the 4H-SiC-based IMPATT device is better than its GaN counterpart, the overall terahertz performance of the unilluminated GaN IMPATT device is far better than the 4H-SiC-based device, particularly in terms of output power and efficiency. The simulation results and the proposed experimental methodology presented here can be used for realizing optically tuned WBG IMPATT oscillators for terahertz communication.

Time and real space dependence of impact ionization events in low noise impact avalanche transit time diodes

Impact avalanche transit time (IMPATT) diodes are an important source of radio-frequency power at millimeter and submillimeter wavelengths. However, exploitation of these devices has been restricted, as they are commonly believed to suffer from high noise levels. In this article, we demonstrate that a heterostructure IMPATT diode has the potential for almost noise-free operation. Our analysis is based on a Monte Carlo simulation of oscillating IMPATT devices.

Microwave and millimeter-wave power generation in silicon carbide avalanche devices

Silicon carbide (SiC), due to its thermal and electronic properties, has long been considered an excellent device material for microwave and millimeter-wave power generation. Numerical simulations were performed to study the typical power generating capabilities of SiC impact avalanche transit-time (IMPATT) diodes utilizing the recent experimental data available. Operating characteristics of double-drift IMPATT devices at 10, 35, 60 and 94 GHz are compared. Both pulsed mode and continuous-wave (cw) mode operation are studied. Finally, a comparison among SiC, Si, and GaAs double-drift IMPATT devices is made at various frequencies. It is shown that, for the pulsed mode of operation, SiC double-drift IMPATT devices can produce significantly higher powers than Si and GaAs devices at comparable frequencies. In the cw mode of operation, SiC devices can produce significantly more power than GaAs devices at all frequencies. However, a comparison at 94 GHz indicates that SiC IMPATT diodes in the cw mode of operation produce power levels comparable to Si IMPATT devices. At lower frequencies the performance of SiC diodes operating in the cw mode is expected to be better than the performance of Si devices due to the better thermal conductivity of SiC.