Abstract Transfer of nitride heterostructures onto diamond substrates using wafer-bonding technology is a promising approach for fabricating nitride devices with superior heat dissipation and output performance compared with devices fabricated on conventional substrates. A critical step in this process is the temporary fixing of the heterostructure surface to a support substrate prior to growth-substrate removal and subsequent bonding to diamond. In this work, we investigate the impact of this preprocessing step on the electrical properties of AlGaN/GaN heterostructures, which are later transferred to diamonds using surface-activated bonding (SAB). The performance of high-electron-mobility transistors and the capacitance-voltage characteristics of gate contacts fabricated on the transferred heterostructures are analyzed. The results demonstrate that temporary fixing using thermoplastic wax preserves the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface, showing no significant electrical degradation after transfer. In contrast, heterostructures temporarily fixed to support substrates using SAB exhibit indications of 2DEG depletion. Furthermore, the thermoplastic-wax-based process achieves a substantially higher transfer yield. These results highlight the advantages of thermoplastic wax for temporary fixing, enabling both preservation of the intrinsic electrical properties of AlGaN/GaN heterostructures and reliable high-yield transfer to diamond substrates. The proposed approach provides a practical route toward the fabrication of advanced nitride-on-diamond devices.
Tungsten has become widely employed as a contact metal in semiconductor devices due to its favorable material properties and process compatibility, with chemical mechanical polishing (CMP) being a crucial step in W contact formation. In this study, oxidation-induced bridge defects which occurred after tungsten CMP were characterized with optical metrology, electron microscopy, EDX, and electrical test measurements. To understand the mechanism of defect formation, the effect of CMP slurry composition, humidity, as well as dielectric material composition was investigated, leading to the elucidation of a mechanism involving a two-step corrosion of W accelerated by dielectric-induced galvanic corrosion. A multipronged strategy to address the root causes achieved the near elimination of the defects, illustrating the value of the mechanistic analysis.
Understanding and controlling the flatband voltage ( V FB ) of gate stacks is critical for the low-temperature fabrication of advanced Ge-based devices. In this study, we investigate the mechanism of V FB modulation in SiO 2 /GeO 2 /Ge gate stacks formed by an electron cyclotron resonance (ECR) plasma process at 130 °C, followed by post-deposition annealing (PDA) at 210 °C–450 °C. Electrical characterization revealed that V FB and hysteresis strongly depend on annealing time. A systematic analysis of capacitance–voltage characteristics indicates that both the interface dipole ( δ dipole ) and fixed charge ( Q fix ) change dynamically during annealing, including polarity inversion of Q fix and gradual weakening of δ dipole . To clarify the origin of these modulations, structural analyses were performed using X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. The results reveal the formation of Ge suboxides and the outward diffusion of Ge oxide species toward the SiO 2 . These phenomena are attributed to the generation and migration of oxygen vacancies within the GeO 2 layer. The oxygen vacancies simultaneously act as positive Q fix and modulate the δ dipole by redistributing charge at the SiO 2 /GeO 2 interface. These findings provide a comprehensive model linking chemical reactions, defect dynamics, and electrical properties, offering a pathway to precise V FB control in low-temperature Ge-based device technologies.
Floating photovoltaic (FPV) systems can benefit from water-assisted thermal conditions and provide a platform for evaluating high-power-density photovoltaic technologies. In this study, mechanically stacked four-terminal (4T) HJT–HJT Si tandem cells were experimentally characterized, and the measured small-area device performance was used as the basis for an M10-equivalent module projection. The projected module parameters were then implemented in PVsyst 8.0 to simulate a 2 MW FPV system and to compare its performance with an HJT single-junction reference under identical site and orientation assumptions. At the selected 10° tilt condition, the HJT–HJT tandem-based model produced approximately 2192 MWh yr −1 , compared with 2172 MWh yr −1 for the HJT reference, corresponding to an approximately 0.92% increase in annual energy yield. The corresponding performance ratio (PR) increased from 82.0% to 83.1%, i.e. by 1.1 percentage points. The simulated PR remained highest in the mid-tilt region, while the seasonal loss hierarchy was similar for both technologies, with mismatch loss remaining the dominant modeled electrical loss. These results indicate a modest system-level advantage for the tandem-based case under the defined assumptions, while the projected plant-level values should be interpreted separately from the experimentally measured cell-level results.
Abstract This work investigates Sc 0.16 Al 0.77 Ga 0.07 N/AlN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with gate field-plate (GFP) design. ScAlGaN quaternary barrier was devised to enhance polarization-induced carrier density and improve carrier confinement. In addition, a GFP structure fabricated by using an offset-exposure technique was implemented to improve dynamic switching characteristics. High-k and wide-bandgap Al 2 O 3 dielectric was deposited by the non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique to simultaneously serve as the gate dielectric and surface passivation layer. The present Sc 0.16 Al 0.77 Ga 0.07 N/AlN/GaN MOS-HFET design has demonstrated a maximum drain-source current density ( I DS, max ) of 1759.0 mA/mm, a maximum extrinsic transconductance ( g m, max ) of 214.0 mS/mm, an on-resistance ( R on ) of 7.3 Ω-mm, and an on/off-current ratio ( I on / I off ) of 1.6 × 10 8 . Improved dynamic on-resistance ( R on, dy ) characteristics together with a cutoff frequency ( f T ) of 41.2 GHz and a maximum oscillation frequency ( f max ) of 48.2 GHz have also been achieved. Furthermore, photosensing characteristics were also demonstrated under 350-nm UV illumination, exhibiting a spectral responsivity (SR) of 104.3 A/W. The obtained results demonstrate that the present design is promisingly advantageous to high-power and high-frequency and deep-UV photosensing applications.
