https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/ell2.12058

Millimetre‐wave high–low IMPATT source development: First on‐chip experimental verification

https://iopscience.iop.org/article/10.1088/1361-6641/abcb1b/pdf

Improved performance of Ni/GaN Schottky barrier impact ionization avalanche transit time diode with n-type GaN deep level defects

X-ray mammography is popularly used for breast cancer screening and monitoring since past several years However, X-Ray is considered to be an ionizing radiation that may lead to secondary cancer development An alternative approach is the Terahertz (T-Ray) hyperthermia technique This paper will report on an in-silico T-ray thermal imaging and detection system for breast cancer identification and screening For this, a super-lattice (GaN/AlxGa1-xN) p++-n--n-n++ type room temperature semiconductor Terahertz source (radiation within 01 THz− 10 THz regime) was designed A modified Quantum Corrected Non-Linear Drift-Diffusion (m-QCNLDD) numerical model is developed and used for this purpose An equivalent circuit model is developed and analysed for obtaining impedance and admittance characteristics The device can generate non-ionizing RF power∼6 × 1010 Wm−2 at 01 THz and ∼043 × 1010 Wm−2 at 10 THz Further, the authors have verified the newly proposed numerical model by comparing the results with experimental observations Finally, the m−QCNLDD simulator coupled with COMSOL Multi-physics® software has been used for generating microwave and T-ray thermographs of healthy and cancerous breast tissues The authors have made a comparative study between microwave and terahertz thermographs for relative accuracy determination The breast tumour (∼3 mm diameter) detection accuracy has been enhanced greatly in the T−ray thermograph studies To the best of authors' knowledge, this is the first in-silico study report on Terahertz wave versus microwave thermography for breast cancer detection

Super-lattice GaN/AlxGa1-xN nanoscale MITATT oscillator as Terahertz radiation source: Novel application in breast cancer imaging

In this article, a novel lateral Schottky barrier high-low impact-ionization-avalanche-transit-time (IMPATT) diode, i.e., the high-electron mobility transistor (HEMT)-like IMPATT (HIMPATT) diode, is proposed based on the AlGaN/GaN 2-D electron gas (2-DEG). Numerical simulation demonstrated that the HIMPATT diode shows better characteristics than the conventional vertical IMPATT diode because of a superior property of the AlGaN/GaN 2-DEG. Comparing with the vertical IMPATT diode, the optimum frequency of HIMPATT diode rises from 260 to 380 GHz, the maximum RF output power <inline-formula> <tex-math notation="LaTeX">${P}_{RF}$ </tex-math></inline-formula> rises from 2.30 to 3.06 MW/cm<sup>2</sup>, and the maximum conversion efficiency <inline-formula> <tex-math notation="LaTeX">$\eta $ </tex-math></inline-formula> rises from 14.7% to 18.5%. In addition, simulation results reveal that the trench length <inline-formula> <tex-math notation="LaTeX">${L}_{r}$ </tex-math></inline-formula> and depth <inline-formula> <tex-math notation="LaTeX">${D}_{r}$ </tex-math></inline-formula> of the 2-DEG channel significantly influence the output performances of HIMPATT diode, where the frequency characteristic is more sensitive to the trench length <inline-formula> <tex-math notation="LaTeX">${L}_{r}$ </tex-math></inline-formula> and the RF power characteristic is more sensitive to the trench depth <inline-formula> <tex-math notation="LaTeX">${D}_{r}$ </tex-math></inline-formula>. By designing the pattern shape of the trench area, a monolithic integrated HIMPATT diode oscillator array can be implemented on one chip to generate a wider frequency band with great RF performances than the vertical IMPATT diode. It provides more variable designing options for the applications of the HIMPATT diode in the terahertz regime.

Simulation Study of Lateral Schottky Barrier IMPATT Diode Based on AlGaN/GaN 2-DEG for Terahertz Applications

High electron mobility effect in band-engineered GaN/quasi-AlGaN based exotic avalanche transit time diode arrays: application as ultra fast THz switches

Modelling/simulation and high-frequency characterization of hetero-junction Avalanche Transit Time (ATT) oscillators, operating in tuned harmonic mode, are reported in the paper. An equivalent circuit, that incorporates self-consistent, non-linear, single-frequency impedance and admittance properties of the device at fundamental, 1st harmonic and 2nd harmonic mode of oscillation frequencies within the THz (0.5–1.5 THz) domain, is simulated. The prospects of Si/4H-SiC versus Si/6H-SiC exotic hetero structures are studied and compared for the generation of considerable amount of RF-power at higher harmonic THz region. For this, a generalised non-linear Mixed Quantum Drift Diffusion (MQDD) model is developed indigenously. The authors have made the simulator realistic by incorporating the temperature dependent carrier ionization rate, saturation drift velocity, mobility and effective mass of the base material-pairs in the analysis. In addition to these, the effects of punch-through phenomena as well as parasitic series resistance related detrimental issues are duly addressed in the present analysis. The authors have made the model realistic by studying the performance of the proposed novel structures under room temperature as well as under elevated temperature conditions. Due to the incorporation of hetero-structure in the active region of the device, considerable amount of power could be generated at 2nd harmonic oscillation frequency (~ 1.7 THz). The study shows that both the Si/4H-SiC and Si/6H-SiC hetero-junction devices are oscillating at 0.5 THz (fundamental frequency). Si/4H-SiC hetero-junction device, due to its less lattice mismatch factor, is more efficient (45%) than its Si/6H-SiC (15%) counterpart under similar structural/electrical/thermal operating conditions. The validity of the MQDD model is established in this paper by comparing the data with corresponding experimental observations at microwave/millimeter-wave region. To the best of authors’ knowledge, this is the first report on harmonic power generation from Si/4H-SiC and Si/6H-SiC hetero-junction ATT devices at higher terahertz region.

Si/SiC heterostructure MITATT oscillator for higher-harmonic THz-power generation: theoretical reliability and experimental feasibility studies of quantum modified non-linear classical model

Numerical analysis followed by experimental investigations are done with heterostructure GaN/AlGaN single drift MIxed Tunnelling and Avalanche Transit Time (MITATT) devices grown on Si〈111〉 substrate, at around 1 THz. A generalised self-consistent, nonlinear Mixed Quantum Drift-Diffusion (MQDD) simulator is developed and used for designing p++-n−-n-n++ type room temperature solid-state source within 0.75–1.1 THz regime. The epitaxial heterojunction layers are grown by III–V nitride molecular beam epitaxy which has enabled the realisation of GaN/AlGaN periodic structure on Si〈111〉 substrate with AlN buffer layer. For the first time, the realisation of heterostructure III–V Nitride MITATT oscillator at sub-mm wave/terahertz (THz) frequencies is done. The device is observed to oscillate at 1 THz with ∼4%. A comparison of MQDD model with experimental (On wafer DC testing) results for heterojunction GaN/AlGaN MITATT diodes shows generalised agreement in terms of breakdown voltage (∼27 V) and efficiency (∼4%). First experimental results of GaN/AlGaN heterostructure MITATT diode are reported and compared with the theoretical predictions obtained through MQDD model.

Design and development of an AlGaN/GaN heterostructure nano-ATT oscillator: experimental feasibility studies in THz domain

Self-consistent non-linear physics based predictive model for the computation of THz-signal attenuation in fog with varying visibility in tropical climatic zone

In this work, a fast subspace identification method for estimating LTI state-space models corresponding to large input-output data is proposed. The algorithm achieves lesser RAM usage, reduced data movement between slow (RAM) and fast memory (processor cache), and introduces a novel method to estimate input (B) and feedforward (D) matrices. By design, the proposed algorithm is specially well-suited to identify multi-scale systems with both fast and slow dynamics. Identification of these systems require high-frequency data recordings over prolonged periods, leading to large input-output data sizes. For such large data sizes, the proposed algorithm outperforms the MATLAB-MOESP method in terms of memory cost, flop-count, and computation time. The effectiveness of the proposed algorithm is established by theoretical computations and various case studies.

Fast Subspace Identification for Large Input-Output Data

In this article, a novel fast subspace identification method for estimating combined deterministic-stochastic LTI state-space models corresponding to large input-output data is proposed. The algorithm achieves lesser runtime RAM usage, reduced data movement between slow (RAM) and fast memory (processor cache), and introduces a novel fast method to estimate input (B), feedforward (D) and steady state Kalman gain (K) matrices. By design, the proposed algorithm is specially well-suited to identify multi-scale systems with both fast and slow dynamics. Identification of these systems require high-frequency data recordings over prolonged periods, leading to large input-output data sizes. For such large data sizes, the proposed algorithm outperforms the conventional subspace methods like N4SID and MOESP in terms of memory-cost, flop-count, and computation time. The effectiveness of the proposed algorithm is established by theoretical analysis, various case studies including estimation of practical systems like a nuclear reactor and by comparison with existing fast subspace methods in the literature.

Debraj Chakraborty

Papers

Si/SiC heterostructure MITATT oscillator for higher-harmonic THz-power generation: theoretical reliability and experimental feasibility studies of quantum modified non-linear classical model

Design and development of an AlGaN/GaN heterostructure nano-ATT oscillator: experimental feasibility studies in THz domain

Self-consistent non-linear physics based predictive model for the computation of THz-signal attenuation in fog with varying visibility in tropical climatic zone

Fast Subspace Identification for Large Input-Output Data

Fast Multivariable Subspace Identification (FMSID) of Combined Deterministic-Stochastic/General LTI Systems for Large Input-Output Data