This study presents the characteristics of HfAlO films for a series of Al incorporation ratios into a HfO₂ dielectric by atomic layer deposition on a Si substrate. A small amount of Al doping into the HfO₂ film can stabilize the tetragonal phase of the HfO₂, which helps to achieve a higher dielectric constant (k) and lower leakage current density, as well as a higher breakdown voltage than HfO₂ film on its own. Moreover, assimilation of Al₂O₃ into HfO₂ can reduce the hysteresis width and frequency dispersion. These are indications of border trap reduction, which was also verified by the border trap extraction mechanism. X-ray photoelectron spectroscopy (XPS) analysis also verified the HfAlO microstructural properties for various Al compositions. In addition, higher amounts of Al₂O₃ in HfAlO resulted in better interface and dielectric behavior through trap minimization, although the equivalent-oxide-thickness (EOT) values show the opposite trend.

In this paper, we report an L _g = 25 nm InGaAs/InAlAs HEMT on InP substrate that delivers excellent high-frequency characteristics. The device exhibited a value of maximum transconductance (g _{m_max}) = 2.8 mS μm⁻¹ at V _DS = 0.8 V and on-resistance (R _ON) = 279 Ω μm. At I _D = 0.56 mA μm⁻¹ and V _DS = 0.5 V, the same device displayed an excellent combination of f _T = 703 GHz and f _max = 820 GHz. To the best of the authors’ knowledge, this is the first demonstration of a transistor with both f _T and f _max over 700 GHz on any material system.

We report the impact from channel composition on the cryogenic low-noise performance at low dc power for a 100-nm gate-length InGaAs-InAlAs-InP high-electron mobility transistor (HEMT). Two indium (In) channel compositions, 65% and 80%, were studied by dc and RF characterization at 300 and 5 K. For the cryogenic low-noise optimization, it was important to increase the transconductance to gate–source capacitance ratio in the weak inversion region implying that a higher maximum cutoff frequency in the HEMT does not guarantee lower noise. The HEMT noise performance was obtained from noise measurements in a hybrid three-stage 4–8-GHz ( ${C}$ -band) low-noise amplifier (LNA) down to 300- $\mu \text{W}$ dc power dissipation. While the HEMT LNA noise performance for both the channel compositions at 300 K was found to be comparable, the HEMT LNA at 5 K with 65% In channel showed a minimum noise temperature of 1.4 K, whereas the noise temperature in the HEMT LNA with 80% In channel HEMTs increased to 2.4 K. The difference in the noise became more pronounced at reduced dc power dissipation. The ultralow dc power of $300 \mu \text{W}$ demonstrated for a cryogenic ${C}$ -band LNA with an average noise temperature of 2.9 K and 24-dB gain is of interest for future qubit read-out electronics at 4 K.

We present our latest results on L _g = 87 nm InAlAs/InGaAs high-electron-mobility transistors with an excellent combination of dc and high-frequency characteristics. We obtained a maximum transconductance of 3 S/mm at V _DS = 0.9 V, an ON-resistance of 273 Ω-μm, a current gain cutoff frequency of 559 GHz, and a maximum oscillation frequency of 671 GHz. According to small-signal modeling, these outstanding device metrics are a consequence of the indium-rich InGaAs channel with very high Hall mobility, compact device design with L _SD = 1 μm, and an optimized gate process that yields well-tempered behavior.

Herein, we present a detailed analysis of the effects of O2 plasma treatment on the AlGaN barrier volume trap states in an Al0.45Ga0.45N/GaN high-electron mobility transistor. Compared to that of the as-grown sample, the single short-pulse ${I}_{D}$ – ${V}_{\text {GS}}$ characterization of the plasma-treated sample exhibited lower charge trapping inside the AlGaN barrier. The 1/ ${f}$ low-frequency noise characterization revealed a significant reduction of approximately 67% in the volume trap density of the AlGaN barrier layer after O2 plasma treatment. This was achieved by the formation of Al–O and Ga–O bonds via the penetration of oxygen ions into the AlGaN bulk, which resulted in reduced trap state density in the AlGaN barrier. In addition, the Schottky characteristics were improved notably. Consequently, the O2 plasma-treated sample did not display current collapse and showed steady drain current output under the reverse-sweep drain-stress bias conditions. Furthermore, the plasma treatment significantly reduced the RF transconductance ( ${g}_{m}$ ) collapse in the as-grown sample, and significantly increased the ${f}_{T}/{f}_{\text {max}}$ of the plasma-treated sample from 65/70 to 120/230 GHz for ${L}_{g}$ = 80 nm devices, respectively. Last, the O2 plasma-treated sample showed substantial improvements in ${P}_{\text {out}\_\max}$ , power added efficiency (PAE), and linear gain from 1.25 W/mm, 20%, and 15 dB to 2.4 W/mm, 50%, and 19 dB, respectively.

We presented an explicit empirical model of the thermal resistance of AlGaN/GaN high-electron-mobility transistors on three distinct substrates, including sapphire, SiC, and Si. This model considered both a linear and non-linear thermal resistance model of AlGaN/GaN HEMT, the thickness of the host substrate layers, and the gate length and width. The non-linear nature of channel temperature—visible at the high-power dissipation stage—along with linear dependency, was constructed within a single equation. Comparisons with the channel temperature measurement procedure (DC) and charge-control-based device modeling were performed to verify the model’s validity, and the results were in favorable agreement with the observed model data, with only a 1.5% error rate compared to the measurement data. An agile expression for the channel temperature is also important for designing power devices and monolithic microwave integrated circuits. The suggested approach provides several techniques for investigation that could otherwise be impractical or unattainable when utilizing time-consuming numerical simulations.