In this paper, a comprehensive evaluation of thermal behavior of the GaN vertical n⁺-n⁻-n-n⁺ Gunn diode have been carried out through simulation method. We explore the complex effects of various parameters on the device thermal performance through a microscopic analysis of electron movements. These parameters include operation bias, doping level, and length of the active region. The increase of these parameters aggravates the self-heating effect and degrades the electron domains, which therefore reduces the overall performance output of the diode. However, appropriate increase of the doping level of active region makes the lattice heat distribute more uniformly and improves the device performance. For the first time, we propose the transition domain, which is in between the dipole domain and accumulation layer, and stands for the degradation of the electron domain. We have also demonstrated that dual domains occur in the device with longer active region length and higher doping level under EB (Energy balance) model, which enhances the harmonics component. Electric and thermal behaviors analysis of GaN vertical Gunn diode makes it possible to optimize the device.

GaN-based planar Gunn diodes are promising terahertz sources for monolithic microwave and terahertz integrated circuits (MMICs and MTICs, respectively) due to high output power and easiness of fabrication and circuit integration. However, high lateral current in the 2DEG channel may lead to failures such as early breakdown and suppression of oscillations. In this paper, we will, for the first time, systematically investigate the thermal effect on DC IV and output RF characteristics of AlGaN/GaN hetero-structural planar Gunn diodes on different substrates including diamond, SiC, Si and sapphire. Our simulation results show that the best RF output performance comes with the devices on diamond substrate and no oscillating current is observed for devices on sapphire substrate. The suppress of Gunn oscillation in the device on sapphire is mainly due to the excessive heat generated in the channel that leads to increase of the dead zone and attenuation of electronic domains. These results will lay theoretical and experimental foundation for realizing not only milliwatt GaN-based terahertz semiconductor oscillators but also other power devices.

Because of the high electron mobility and electron velocity in the channel, InAs/AlSb high electron mobility transistors (HEMTs) have excellent physical properties, compared with the other traditional III-V semiconductor components, such as ultra-high cut-off frequency, very low power consumption and good noise performance. In this paper, both the structure and working principle of InAs/AlSb HEMTs were studied, the energy band distribution of the InAs/AlSb heterojunction epitaxy was analyzed, and the generation mechanism and scattering mechanism of two-dimensional electron gas (2DEG) in InAs channel were demonstrated, based on the software simulation in detail. In order to discuss the impact of different epitaxial structures on the 2DEG and electron mobility in channel, four kinds of epitaxies with different thickness of InAs channel and AlSb upper-barrier were manufactured. The samples were evaluated with the contact Hall test. It is found the sample with a channel thickness of 15 nm and upper-barrier layer of 17 nm shows a best compromised sheet carrier concentration of 2.56 × 10¹² cm⁻² and electron mobility of 1.81 × 10⁴ cm²/V·s, and a low sheet resistivity of 135 Ω/□, which we considered to be the optimized thickness of channel layer and upper-barrier layer. This study is a reference to further design InAs/AlSb HEMT, by ensuring a good device performance.

In this paper, a novel gallium nitride (GaN)-based heterostructure Gunn diode is proposed for the first time to enhance the output characteristics of Gunn oscillation waveforms. A well-designed grooved anode contact is adopted to separate the long-channel diode into two short-channel diodes in parallel. If the grooved anode contact is positioned in the middle of the device, the output power nearly doubles in the grooved-anode diode compared with the single-channel ones, as does the output frequency. Based on the numerical results, the best output characteristics are obtained at the 2.0-µm symmetrical grooved-anode diode, which produces nearly 5.48 mW of power at the fundamental frequency of 172.81 GHz, with 3.13% efficiency of power conversion. If the grooved anode contact is not positioned in the middle of the diode, the harmonic frequency would be enhanced. The GaN heterostructure grooved-anode Gunn diode has been demonstrated to be an excellent solid-state source of terahertz oscillator.

In this paper, we propose a novel design of GaN-based planar Gunn oscillator as terahertz signal source. The oscillator has multiple gates and each gate can be individually biased. By controlling gate bias voltage and distance to the barrier layer, the output oscillating current can be formed in such a way that the higher harmonics are more powerful than the fundamental one. This is because multiple Gunn domains created under the gates in the channel are synchronized. Compared to the conventional single-domain diode, this multi-gate configuration not only increases the frequency and output power but also provides superior harmonic control, leading to higher efficiency and more stable operation at terahertz frequencies. We will review the design details and analysis on domain forming conditions using a physics-based numerical model. The optimal parameters for high power, high DC-RF conversion efficiency and high frequency will be given. Specifically, in dual-gate device, when it works in the dual-domain mode, the second harmonic is enhanced, reaching a frequency of 310.5 GHz with 7.6 mW of power and 11.2% efficiency. The tri-gate device operating in tri-domain mode further enhances the third harmonic to 417.0 GHz, with 9.57 mW of power and 9.23% efficiency. The multi-gate structure allows for more efficient harmonic generation, greater frequency tunability, and better power management, all of which are crucial for advanced terahertz application such as mixing, frequency multiplexing, and signal amplification.

A compact differential microwave sensor, based on an “eye-like” complementary split-ring resonator (CSRR), for complex permittivity detection to address the dual challenges of mitigating interresonator coupling and achieving a high sensitivity, is proposed in this work. The “eye-like” CSRR is split into two separate differential half-CSRRs by a slot gap with a “ocular pupil” (OP) at the center; thus, a differential sensing mode against environmental common mode interference is realized. By optimizing the slot gap space and the radii of the “OP,” the interresonator coupling is minimized. Moreover, by integrating two symmetric interdigital structures on both upper and lower “eyelids,” the electrical field distribution is intensified substantially, thereby enhancing sensitivity. The geometry and dimensions of the sensor are optimized based on a mathematical analysis of an equivalent lumped RCL circuit model of CSRR, which also provides the design principle of the sensor. The developed sensor is fabricated and tested with a compact geometric size of 19×14×0.76 mm. The device prototype is measured and characterized using water–ethanol solutions. Compared with the previous similar works, the sensor is small in size and has a high frequency detection resolution (FDR) of 20.1 MHz/ $\Delta \varepsilon ^{\prime }$ , with a sample volume as small as $0.41~\mu $ L.