In this article, GaN/AlGaN metal–oxide–semiconductor high-electron-mobility field-effect transistors (MOSHEMTs) fabricated on high-resistivity Si (111) substrates have been evaluated using low-frequency (LF) noise measurement. The noise power spectral density (PSD) of devices with different lengths and channel orientations has been characterized in linear operation. No noticeable differences in the electrical and noise PSD characteristics have been observed between the GaN [ $1\overline {1}00$ ] and [ $11\overline {2}0$ ] channel orientations. While most devices are dominated by 1/ ${f}$ noise, originating from number fluctuations, for long devices ( ${L} \ge 1.1~\mu \text{m}$ ), additional generation–recombination (GR) noise has been observed, originating from traps in the GaN layer.

This study reports the impact of forming gas annealing (FGA) on the electrical characteristics of sulfur passivated, atomic layer deposited Al₂O₃ gate dielectrics deposited on (110) oriented n- and p-doped In_0.53Ga_0.47As layers metal-oxide-semiconductor capacitors (MOSCAPs). In combination, these approaches enable significant Fermi level movement through the bandgap of both n- and p-doped In_0.53Ga_0.47As (110) MOSCAPs. A midgap interface trap density (D_it) value in the range $0.87-1.8\times {10}^{12}\hspace{0.17em}{\text{cm}}^{-2}{\text{eV}}^{-1}$ is observed from the samples studied. Close to the conduction band edge, a D_it value of $3.1\times {10}^{11}\hspace{0.17em}{\text{cm}}^{-2}{\text{eV}}^{-1}$ is obtained. These data indicate the combination of sulfur pre-treatment and FGA is advantageous in passivating trap states in the upper half of the bandgap of (110) oriented In_0.53Ga_0.47As. This is further demonstrated by a reduction in border trap density in the n-type In_0.53Ga_0.47As (110) MOSCAPs from $1.8\times {10}^{12}\hspace{0.17em}{\text{cm}}^{-2}$ to $5.3\times {10}^{11}\hspace{0.17em}{\text{cm}}^{-2}$ as a result of the FGA process. This is in contrast to the observed increase in border trap density after FGA from $7.3\times {10}^{11}\hspace{0.17em}{\text{cm}}^{-2}$ to $1.4\times {10}^{12}\hspace{0.17em}{\text{cm}}^{-2}$ in p-type In_0.53Ga_0.47As (110) MOSCAPs, which suggest FGA is not as effective in passsivating states close to the valence band edge.

We extract an AlGaN surface state spectrum with a density ( ${D}_{\text{SS}}$ ) ranging between $1.4\times10$ ¹² and $4.7\times10$ ¹² eV ⁻¹ cm ⁻² . The low ${D}_{\text{SS}}$ is achieved with in situ SiN passivation. ${D}_{\text{SS}}$ is extracted from ungated AlGaN/AlN/GaN heterostructures with varied AlN thicknesses between 0 and 2 nm: increased AlN thicknesses in heterostructures monotonously increase two-dimensional electron gas (2DEG) densities ${N}_{\text{sh}}$ and AlGaN surface potential energies ${q} {\varphi } _{\text{s}}$ , and ${D}_{\text{SS}}$ is extracted with $\boldsymbol {\Delta } {N}_{\text{sh}}$ – $\boldsymbol {\Delta } {\varphi }_{\text{s}}$ correlations. The ${D}_{\text{SS}}$ extraction methodology in this work features calibrated polarization charge values, Hartree approximation-based 2DEG profile calculation, and incorporated C-doped GaN (C-GaN) substrate impact on 2DEG. We also extract the charge neutrality level at the AlGaN surface, which is ~0.95 eV below conduction band minimum.

In this work, the impact of ammonium sulfide ((NH₄)₂S) surface treatment on the electrical passivation of the Al₂O₃/p-GaSb interface is studied for varying sulfide concentrations. Prior to atomic layer deposition of Al₂O₃, GaSb surfaces were treated in 1%, 5%, 10%, and 22% (NH₄)₂S solutions for 10 min at 295 K. The smallest stretch-out and flatband voltage shifts coupled with the largest capacitance swing, as indicated by capacitance-voltage (CV) measurements, were obtained for the 1% treatment. The resulting interface defect trap density (D_it) distribution showed a minimum value of 4 × 10¹²cm⁻²eV⁻¹ at E_v + 0.27 eV. Transmission electron microscopy and atomic force microscopy examination revealed the formation of interfacial layers and increased roughness at the Al₂O₃/p-GaSb interface of samples treated with 10% and 22% (NH₄)₂S. In combination, these effects degrade the interface quality as reflected in the CV characteristics.

We demonstrate high linearity of fully processed GaN on 2-mm high resistivity (HR) Si wafers with high effective resistivity ( $\rho_{\mathbf{eff}}$ $>$ 2 k $\Omega $ $\cdot$ cm). Using two common-gate (MOS-)HEMT devices presenting different levels of distortion as demonstrators, we discuss the impact of substrate-induced harmonic distortion (HD) on RF switches. By comparing switch and CPW line measurements, it is possible to estimate the substrate contribution to HD. For the relatively nonlinear device, the intrinsic device nonlinearities dominate by a 16–20-dB margin over the substrate contribution. For a more linear device ( $-$ 110 dBc of second harmonic power at 900 MHz and P $_{\mathbf{in}}$ $=$ 15 dBm), the substrate distortion contributes equally to channel nonlinearity, highlighting the necessity of engineering the substrate’s RF performance together with the transistor. We provide guidelines for substrate $\rho_{\mathbf{eff}}$ to achieve good switch linearity for given device harmonic levels.

We have developed a novel Josephson junction geometry with minimal volume of lossy isolation dielectric, being suitable for higher quality trilayer junctions implemented in qubits. The junctions are based on in-situ deposited trilayers with thermal tunnel oxide, have micron-sized areas and a low subgap current. In qubit spectroscopy only a few avoided level crossings are observed, and the measured relaxation time of $T_1approx400; m{nsec}$ is in good agreement with the usual phase qubit decay time, indicating low loss due to the additional isolation dielectric.