α-SiC nanoscale transit-time diodes: performance of the photo-irradiated terahertz sources at elevated temperature
TL;DR: In this paper, the effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p++ p n n++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments.
Abstract: The effects of elevated junction temperature on the terahertz (THz) frequency characteristics of α-(hexagonal, 4H and 6H) silicon carbide (SiC) based double-drift region (DDR, p++ p n n++ type) impact ionization avalanche transit-time (IMPATT) devices are studied and compared for the first time through simulation experiments. This study reveals that at 300 K < T < 600 K, a 4H-SiC IMPATT diode may yield 3.5 W of output power (efficiency (η) ~ 8.6%) at 1.3 THz, while its 6H-SiC counterpart can deliver 3 W of output power (η = 6.3%) at 1.2 THz. It is interesting to observe that at elevated temperature, the performance of a 6H-SiC IMPATT diode degrades more in comparison with its 4H-SiC counterpart. These comparative analyses reveal the superiority of 4H-SiC diodes over their 6H-SiC counterparts, and thus establish the potential of the former as a high-power THz IMPATT oscillator even in harsh environments. Mobile space charge effects and the effect of positive series resistance on the high-temperature performance of the THz devices are also simulated, and it is found that series resistance reduces the output power level of the diodes by at least 15.0%. Moreover, the effects of increased junction temperature on the photo-sensitivity of top mounted (TM) and flip chip (FC) α-SiC IMPATTs are also investigated using a modified simulation technique. The device operating frequencies, under TM illumination configuration, shifts upward by at least 40.0 GHz, whereas the operating frequency shifts upward by at least 100.0 GHz under FC illumination configuration. The simulation results and the proposed experimental methodology presented here may be used for realizing optically controlled α-SiC transit-time devices for application in THz communication.
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TL;DR: In this paper, the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz were presented.
Abstract: In this paper, we have presented the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz. THz electromagnetic wave can permit more densely packed communication links with increased security of communication transmission. The simulated results such as gain, radiation efficiency and 10 dB impedance bandwidth of rectangular microstrip patch antenna at THz frequencies without shorting post configuration are 3.497 dB, 55.71% and 17.76%, respectively, whereas with shorting post configuration, corresponding parameters are 3.502 dB, 55.88% and 17.27%. The simulation has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the method of finite difference time domain technique.
99 citations
01 Jul 2020-Microsystem Technologies-micro-and Nanosystems-information Storage and Processing Systems
TL;DR: In this paper, 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.
Abstract: 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.
8 citations
01 Jan 2020
TL;DR: In this article, a modified Quantum Corrected Non-Linear Drift-Diffusion (m-QCNLDD) numerical model is developed and used for T-ray thermal imaging and detection system for breast cancer identification and screening.
Abstract: 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
3 citations
TL;DR: In this article , a novel lateral Schottky barrier high-low impactionization-avalanche-transit-time (IMPATT) diode is proposed based on the AlGaN/GaN 2-D electron gas (2-DEG).
Abstract: 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 ${P}_{RF}$ rises from 2.30 to 3.06 MW/cm2, and the maximum conversion efficiency $\eta $ rises from 14.7% to 18.5%. In addition, simulation results reveal that the trench length ${L}_{r}$ and depth ${D}_{r}$ of the 2-DEG channel significantly influence the output performances of HIMPATT diode, where the frequency characteristic is more sensitive to the trench length ${L}_{r}$ and the RF power characteristic is more sensitive to the trench depth ${D}_{r}$ . 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.
3 citations
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TL;DR: In this article, the authors presented theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode.
Abstract: This paper presents theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode. A simplified theory is employed to obtain a starting design. This design is then modified to achieve higher efficiency operation as specific device limitations are reached in large-signal (computer) operation. Self-consistent numerical solutions are obtained for equations describing carrier transport, carrier generation, and space-charge balance. The solutions describe the evolution in time of the diode and its associated resonant circuit. Detailed solutions are presented of the hole and electron concentrations, electric field, and terminal current and voltage at various points in time during a cycle of oscillation. Large-signal values of the diode's negative conductance, susceptance, average voltage, and power-generating efficiency are presented as a function of oscillation amplitude for a fixed average current density. For the structure studied, the largest microwave power-generating efficiency (18 percent at 9.6 GHz) has been obtained at a current density of 200 A/cm2, but efficiencies near 10 percent were obtained over a range of current density from 100 to 1000 A/cm2.
2,042 citations
TL;DR: In this article, the absorption spectrum of the explosive 1, 3,5-trinitro-1,3, 5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopic imaging.
Abstract: The absorption spectrum of the explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) has been measured using a conventional Fourier transform infrared spectroscopy and by terahertz pulsed spectroscopy. Seven absorption features in the spectral range of 5–120cm−1 have been observed and identified as the fingerprint of RDX. Furthermore, the spatial distribution of individual chemical substances including RDX, has been mapped out using reflection terahertz spectroscopic imaging in combination with component spatial pattern analysis. This is the terahertz spectroscopy and chemical mapping of explosives obtained using reflection terahertz measurement, and represents a significant advance toward developing a terahertz pulsed imaging system for security screening of explosives.
699 citations
TL;DR: By studying the terahertz pulse shape in the time domain, TPI is able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC) and inflammation and scar tissue.
Abstract: We demonstrate the application of terahertz pulse imaging (TPI) in reflection geometry for the study of skin tissue and related cancers both in vitro and in vivo. The sensitivity of terahertz radiation to polar molecules, such as water, makes TPI suitable for studying the hydration levels in the skin and the determination of the lateral spread of skin cancer pre-operatively. By studying the terahertz pulse shape in the time domain we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC). Basal cell carcinoma has shown a positive terahertz contrast, and inflammation and scar tissue a negative terahertz contrast compared to normal tissue. In vivo measurements on the stratum corneum have enabled visualization of the stratum corneum-epidermis interface and the study of skin hydration levels. These results demonstrate the potential of terahertz pulse imaging for the study of skin tissue and its related disorders, both in vitro and in vivo.
692 citations
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TL;DR: In this article, the authors proposed a platform for the trace detection of explosives based on Nanosensors, which can satisfy all the requirements for an effective platform for detecting trace explosives.
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