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 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.

The reliability instability of inhomogeneous Schottky contact behaviors of Ni/Au and Pt/Ti/Pt/Au gate contacts on AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated via off-state stress and temperature. Under the off-state stress condition, Pt/Ti/Pt/Au HEMT showed abruptly reduced reverse leakage current, which improved the Schottky barrier height (SBH) from 0.46 to 0.69 eV by suppression of the interfacial donor state. As the temperature increased, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT at 308 K showed more reduction under the same off-state stress condition while that of the Ni/Au AlGaN/GaN HEMT increased. However, with temperatures exceeding 308 K under the same off-state stress conditions, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT increases, which can be intensified using the inverse piezoelectric effect. Based on this phenomenon, the present work reveals the necessity for analyzing the concurrent SBH and reliability instability due to the interfacial trap states of the MS contacts.

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.

The characteristics of traps between the Al_0.25Ga_0.75N barrier and the GaN channel layer in a high-electron-mobility-transistors (HEMTs) were investigated. The interface traps at the Al_0.25Ga_0.75N/GaN interface as well as the border traps were experimentally analyzed because the Al_0.25Ga_0.75N barrier layer functions as a dielectric owing to its high dielectric constant. The interface trap density D_it and border trap density N_bt were extracted from a long-channel field-effect transistor (FET), conventionally known as a FATFET structure, via frequency-dependent capacitance–voltage (C–V) and conductance–voltage (G–V) measurements. The minimum D_it value extracted by the conventional conductance method was 2.5 × 10¹² cm⁻²·eV⁻¹, which agreed well with the actual transistor subthreshold swing of around 142 mV·dec⁻¹. The border trap density N_bt was also extracted from the frequency-dependent C–V characteristics using the distributed circuit model, and the extracted value was 1.5 × 10¹⁹ cm⁻³·eV⁻¹. Low-frequency (1/f) noise measurement provided a clearer picture of the trapping–detrapping phenomena in the Al_0.25Ga_0.75N layer. The value of the border trap density extracted using the carrier-number-fluctuation (CNF) model was 1.3 × 10¹⁹ cm⁻³·eV⁻¹, which is of a similar level to the extracted value from the distributed circuit model.