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The paper investigates the terahertz performance of a mutually injection-locked multi-element high electron mobility avalanche transit time (HEM-ATT) source based on AlGaN/GaN two-dimensional electron gas (2-DEG). Utilizing a nanostrip patch type planar coupling circuit, mutual injection locking between adjacent elements is achieved. The paper provides a comprehensive analysis of the integrated power combining technique in the mutually injection-locked multi-element HEM-ATT oscillator. A ten-element mutually injection-locked integrated power combined source is designed for operation at 1.0 THz, and simulation studies are conducted to examine its DC, large-signal, and avalanche noise characteristics. The capability of generating a narrow-band terahertz wave is verified by introducing various levels of structural mismatches between the elements. Results indicate that the ten-element HEM-ATT oscillator can deliver 2.27 W peak power with a 17% DC to THz conversion efficiency at 1.0 THz. The average noise measure of the oscillator is found to be 12.54 dB. Additionally, the terahertz performance of the mutually injection-locked ten-element HEM-ATT oscillator is compared with other state-of-the-art THz sources to evaluate its potentiality as an excellent integrated THz radiator.

A multiple quantum barrier (MQB) avalanche photodiode (APD) structure based on GaN/AlxGa $_{1{-}x}\text{N}$ material system has been proposed in this paper which is capable of detecting infrared (IR) signal up to $6.0~\mu \text{m}$ wavelength. A self-consistent quantum drift-diffusion (SCQDD) model developed by the authors, has been used to determine the current-voltage characteristics under dark and illuminated conditions, spectral response, excess noise properties, signal-to-noise ratio, time and frequency responses. Results show that the proposed MQB APD attains peak responsivity of 60 AW $^{-1}$ at $3.0\, \mu \text{m}$ wavelength. Incorporation of a dedicated thin $n$ -type GaN layer for avalanche multiplication in between the $p^{+}$ -GaN contact layer and MQB constant-field drift-layer ensures significantly low noise equivalent power under normal operating conditions at room temperature (300 K). Optical pulse response of the device reveals that special restriction over the charge multiplication able to supress the minor peaks of the current response and consequently significantly narrow pulse response can be achieved. Narrow pulse response leads to broad bandwidth of 274.5 GHz, which is significantly broader than the existing IR photo-detectors.

In our pursuit of high-power terahertz (THz) wave generation, we propose innovative edge-terminated single-drift region (SDR) multi-quantum well (MQW) impact avalanche transit time (IMPATT) structures based on the AlxGa1−xN/GaN/AlxGa1−xN material system, with a fixed aluminum mole fraction of x = 0.3. Two distinct MQW diode configurations, namely p+-n junction-based and Schottky barrier diode structures, were investigated for their THz potential. To enhance reverse breakdown characteristics, we propose employing mesa etching and nitrogen ion implantation for edge termination, mitigating issues related to premature and soft breakdown. The THz performance is comprehensively evaluated through steady-state and high-frequency characterizations using a self-consistent quantum drift-diffusion (SCQDD) model. Our proposed Al0.3Ga0.7N/GaN/Al0.3Ga0.7N MQW diodes, as well as GaN-based single-drift region (SDR) and 3C-SiC/Si/3C-SiC MQW-based double-drift region (DDR) IMPATT diodes, are simulated. The Schottky barrier in the proposed diodes significantly reduces device series resistance, enhancing peak continuous wave power output to approximately 300 mW and DC to THz conversion efficiency to nearly 13% at 1.0 THz. Noise performance analysis reveals that MQW structures within the avalanche zone mitigate noise and improve overall performance. Benchmarking against state-of-the-art THz sources establishes the superiority of our proposed THz sources, highlighting their potential for advancing THz technology and its applications.

A Schottky barrier high-electron-mobility avalanche transit time (HEM-ATT) structure is proposed for terahertz (THz) wave generation. The structure is laterally oriented and based on AlGaN/GaN two-dimensional electron gas (2-DEG). Trenches are introduced at different positions of the top AlGaN barrier layer for realizing different sheet carrier density profiles at the 2-DEG channel; the resulting devices are equivalent to high–low, low–high and low-high–low quasi-Read structures. The DC, large-signal and noise simulations of the HEM-ATTs were carried out using the Silvaco ATLAS platform, non-sinusoidal-voltage-excited large-signal and double-iterative field-maximum small-signal simulation models, respectively. The breakdown voltages of the devices estimated via simulation were validated by using experimental measurements; they were found to be around 17–18 V. Under large-signal conditions, the series resistance of the device is estimated to be around 20 Ω. The large-signal simulation shows that the HEM-ATT source is capable of delivering nearly 300 mW of continuous-wave peak power with 11% conversion efficiency at 1.0 THz, which is a significant improvement over the achievable THz power output and efficiency from the conventional vertical GaN double-drift region (DDR) IMPATT THz source. The noise performance of the THz source was found to be significantly improved by using the quasi-Read HEM-ATT structures compared to the conventional vertical Schottky barrier IMPATT structure. These devices are compatible with the state-of-the-art medium-scale semiconductor device fabrication processes, with scope for further miniaturization, and may have significant potential for application in compact biomedical spectroscopy systems as THz solid-state sources.

Noise performance of different structures of anisotype heterojunction double-drift region (DDR) mixed tunneling and avalanche transit time (MITATT) devices has been studied. The devices are designed for operation at millimeter-wave W-band frequencies. A simulation model has been developed to study the noise spectral density and noise measure of the device. Two different mole fractions and of Ge and corresponding four types of device structure are considered for the simulation. The results show that the -Si heterojunction DDR structure of MITATT device excels all other structures as regards noise spectral density ( sec) and noise measure (33.09 dB) as well as millimeter-wave properties such as DC-to-RF conversion efficiency (20.15%) and CW power output (773.29 mW).