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.

Large-signal characterization of DDR silicon IMPATTs operating up to 0.5 THz

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).

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

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 generalized analytical model based on multistage scattering phenomena for estimating the impact ionization rate of charge carriers in semiconductors

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.

Quantum drift-diffusion model for 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.

https://iopscience.iop.org/article/10.1088/1674-4926/35/3/034005/pdf

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

The authors have carried out the large-signal characterization of silicon-based double-drift region (DDR) impact avalanche transit time (IMPATT) devices designed to operate up to 0.5 THz using a large-signal simulation method developed by the authors based on non-sinusoidal voltage excitation. The effect of band-to-band tunneling as well as parasitic series resistance on the large-signal properties of DDR Si IMPATTs have also been studied at different mm-wave and THz frequencies. Large-signal simulation results show that DDR Si IMPATT is capable of delivering peak RF power of 633.69 mW with 7.95% conversion efficiency at 94 GHz for 50% voltage modulation, whereas peak RF power output and efficiency fall to 81.08 mW and 2.01% respectively at 0.5 THz for same voltage modulation. The simulation results are compared with the experimental results and are found to be in close agreement.

https://iopscience.iop.org/article/10.1088/1674-4926/34/10/104003/pdf

Large-signal characterization of DDR silicon IMPATTs operating in millimeter-wave and terahertz regime

Herein we report variation in Tunnelling magneto resistance (TMR) of TM-porphyrin against increase in d electrons from n=1 to 8; as the transition metal changes across the periodic table from Sc to Ni. We observed that highest value of TMR is observed for d5 system the TMR becomes gigantic (1022) at the equilibrium and on either side of it we need to apply certain amount of energy to reach appreciable TMR. An even-odd oscillation of TMR is observed against the number of electrons in d orbital. We also observed that with even number of d electrons TMR values is on lower side and in many cases below the accepted range (150%) of an efficient TMR device. In fact, to achieve an acceptable range we need to apply relatively larger energy (as large as 0.7 eV for Ni) probably due to preference of low spin states in presence of even number of electrons in an atom. Observed feature has been explained using molecular orbital obtained in each case.

Even Odd Oscillation in Tunnelling Magneto Resistance of Transition metal doped Metallo Porphyrin systems

We report herein, charge transfer assisted tuning of electronic and spintronic feature of g-C4N3@Lin=1-4 systems. Complete removal of spintronic feature is observed at the doping concentration 14.28%. At lower doping concentration, half metallic feature is observed with clear manifestation of negative differential resistance, which is predominant at n=3. We also noticed significant modifications in current-voltage characteristics as the number of dopants flips from odd to even numbers. Observed feature is mainly attributed to increased charge transfer from Li atom to the g-C4N3 backbone at higher doping concentration and concomitant enhancement in electron-electron interactions. These observations are in corroboration with molecular orbital picture obtained at various doping concentrations.

Jit Chakraborty

Papers

Large-signal characterization of DDR silicon IMPATTs operating up to 0.5 THz

Large-signal characterization of DDR silicon IMPATTs operating in millimeter-wave and terahertz regime

Even Odd Oscillation in Tunnelling Magneto Resistance of Transition metal doped Metallo Porphyrin systems

Role of dopants in tuning spintronic features of lithium doped g-C4N3@Lin =1 to 4