Improvement of AlGaN/GaN High-Electron-Mobility Transistor Radio Frequency Performance Using Ohmic Etching Patterns for Ka-Band Applications.

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances ( and ) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure () with optimized values were measured for 1 μm line OEP HEMTs.

Synthesis of a large area ReS thin film by CVD for in-depth investigation of resistive switching: effects of metal electrodes, channel width and noise behaviour.

The anisotropic crystal structure and layer independent electrical and optical properties of ReS make it unique among other two-dimensional materials (2DMs), emphasizing a special need for its synthesis. This work discusses the synthesis and in-depth characterization of a 1 × 1 cm large and few layered ReS film. Vibrational modes and excitonic peaks observed from the Raman and photoluminescence (PL) spectra corroborated the formation of a ReS film with a 1.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination.

GaN high-electron-mobility transistors (HEMTs) have attracted widespread attention for high-power microwave applications, owing to their superior properties. However, the charge trapping effect has limitations to its performance. To study the trapping effect on the device large-signal behavior, AlGaN/GaN HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) were characterized through X-parameter measurements under ultraviolet (UV) illumination.

Improvement of AlGaN/GaN HEMTs Linearity Using Etched-Fin Gate Structure for Ka Band Applications.

In this paper, AlGaN/GaN high electron mobility transistors (HEMTs) with etched-fin gate structures fabricated to improve device linearity for Ka-band application are reported. Within the proposed study of planar, one-etched-fin, four-etched-fin, and nine-etched-fin devices, which have 50-μm, 25-μm, 10-μm, and 5-μm partial gate widths, respectively, the four-etched-fin gate AlGaN/GaN HEMT devices have demonstrated optimized device linearity with respect to the extrinsic transconductance (Gm) value, the output third order intercept point (OIP3), and the third-order intermodulation output power (IMD3) level. The IMD3 is improved by 7 dB at 30 GHz for the 4 × 50 μm HEMT device.

Effect of High-Pressure GaN Nucleation Layer on the Performance of AlGaN/GaN HEMTs on Si Substrate.

A high-pressure (HP) GaN nucleation layer (NL) was inserted between AlGaN buffer and an unintentionally doped (UID) GaN layer of an AlGaN/GaN HEMT on Si. The XRD and TEM showed that when the V/III ratio was optimized during the HP-GaN NL growth, the edge dislocation density in the HP-GaN NL layer could be reduced significantly. Experimental results exhibited a lower off-state leakage current, higher maximum I and G (corresponding to 22.

Thermal Analysis of Flip-Chip Bonding Designs for GaN Power HEMTs with an On-Chip Heat-Spreading Layer.

In this work, we demonstrated the thermal analysis of different flip-chip bonding designs for high power GaN HEMT developed for power electronics applications, such as power converters or photonic driver applications, with large gate periphery and chip size, as well as an Au metal heat-spreading layer deposited on top of a planarized dielectric/passivation layer above the active region. The Au bump patterns can be designed with high flexibility to provide more efficient heat dissipation from the large GaN HEMT chips to an AlN package substrate heat sink with no constraint in the alignment between the HEMT cells and the thermal conduction bumps. Steady-state thermal simulations were conducted to study the channel temperatures of GaN HEMTs with various Au bump patterns at different levels of current and voltage loadings, and the results were compared with the conventional face-up GaN die bonding on an AlN package substrate.

Surface Acoustic Wave Propagation of GaN/Sapphire Integrated with a Gold Guiding Layer.

Gallium nitride (GaN), widely known as a wide bandgap semiconductor material, has been mostly employed in high power devices, light emitting diodes (LED), and optoelectronic applications. However, it could be exploited differently due to its piezoelectric properties, such as its higher SAW velocity and strong electromechanical coupling. In this study, we investigated the affect of the presence of a guiding layer made from titanium/gold on the surface acoustic wave propagation of the GaN/sapphire substrate.

Role of Boron in Assisting the Super-Enhancement of Emissions from Carbon-Implanted Silicon.

The super enhancement of silicon band edge luminescence when co-implanted with boron and carbon is reported. The role of boron in the band edge emissions in silicon was investigated by deliberately introducing defects into the lattice structures. We aimed to increase the light emission intensity from silicon by boron implantation, leading to the formation of dislocation loops between the lattice structures.

Buffer Traps Effect on GaN-on-Si High-Electron-Mobility Transistor at Different Substrate Voltages.

Substrate voltage (V) effects on GaN-on-Si high electron mobility transistors (HEMTs) power application performance with superlattice transition layer structure was investigated. The 2DEG conductivity and buffer stack charge redistribution can be affected by neutral/ionized donor and acceptor traps. As the donor/acceptor traps are excessively ionized or de-ionized by applying V, the depletion region between the unintentionally doped (UID)/Carbon-doped (C-doped) GaN layer may exhibit a behavior similar to the p-n junction.

A Novel GaN:C Millimeter-Wave HEMT with AlGaN Electron-Blocking Layer.

An AlGaN/GaN/Si high electron mobility transistor (HEMT) using a GaN:C buffer with a 2 nm AlGaN electron-blocking layer (EBL) is investigated for the first time for millimeter-wave applications. Compared with the double heterostructure field effect transistor (DHFET), the AlGaN/GaN HEMT with the GaN:C/EBL buffer has a lower vertical leakage, higher thermal stability, and better RF performance. In addition, AlGaN EBL can prevent carbon-related traps from GaN:C and improve electron confinement in 2DEG during high-frequency operation.

Adoption of the Wet Surface Treatment Technique for the Improvement of Device Performance of Enhancement-Mode AlGaN/GaN MOSHEMTs for Millimeter-Wave Applications.

In this work, a low-power plasma oxidation surface treatment followed by AlO gate dielectric deposition technique is adopted to improve device performance of the enhancement-mode (E-mode) AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) intended for applications at millimeter-wave frequencies. The fabricated device exhibited a threshold voltage (V) of 0.13 V and a maximum transconductance (g) of 484 (mS/mm).

Development of GaN HEMTs Fabricated on Silicon, Silicon-on-Insulator, and Engineered Substrates and the Heterogeneous Integration.

GaN HEMT has attracted a lot of attention in recent years owing to its wide applications from the high-frequency power amplifier to the high voltage devices used in power electronic systems. Development of GaN HEMT on Si-based substrate is currently the main focus of the industry to reduce the cost as well as to integrate GaN with Si-based components. However, the direct growth of GaN on Si has the challenge of high defect density that compromises the performance, reliability, and yield.

Impact of Surface States and Aluminum Mole Fraction on Surface Potential and 2DEG in AlGaN/GaN HEMTs.

The presence of surface traps is an important phenomenon in AlGaN/GaN HEMT. The electrical and physical properties of these surface traps have been analyzed through the study of 2DEG electron concentration along with the variation of aluminum percentage in the barrier layer of HEMT. This analysis shows that from deep to shallow donors, the percentage change in electron density in 2DEG gets saturated (near 8%) with change in aluminum concentration.

Lattice-Matched AlInN/GaN/AlGaN/GaN Heterostructured-Double-Channel Metal-Oxide-Semiconductor High-Electron Mobility Transistors with Multiple-Mesa-Fin-Channel Array.

Multiple-mesa-fin-channel array patterned by a laser interference photolithography system and gallium oxide (GaO) gate oxide layer deposited by a vapor cooling condensation system were employed in double-channel AlInN/GaN/AlGaN/GaN heterostructured-metal-oxide-semiconductors (MOSHEMTs). The double-channel was constructed by the polarized AlGaN/GaN channel 1 and band discontinued lattice-matched AlInN/GaN channel 2. Because of the superior gate control capability, the generally induced double-hump transconductance characteristics of double-channel MOSHEMTs were not obtained in the devices.

The Evolution of Manufacturing Technology for GaN Electronic Devices.

GaN has been widely used to develop devices for high-power and high-frequency applications owing to its higher breakdown voltage and high electron saturation velocity. The GaN HEMT radio frequency (RF) power amplifier is the first commercialized product which is fabricated using the conventional Au-based III-V device manufacturing process. In recent years, owing to the increased applications in power electronics, and expanded applications in RF and millimeter-wave (mmW) power amplifiers for 5G mobile communications, the development of high-volume production techniques derived from CMOS technology for GaN electronic devices has become highly demanded.

Hysteresis in As-Synthesized MoS Transistors: Origin and Sensing Perspectives.

Two-dimensional materials, including molybdenum disulfide (MoS2), present promising sensing and detecting capabilities thanks to their extreme sensitivity to changes in the environment. Their reduced thickness also facilitates the electrostatic control of the channel and opens the door to flexible electronic applications. However, these materials still exhibit integration difficulties with complementary-MOS standardized processes and methods.

State-of-the-Art on Functional Titanium Dioxide-Integrated Nano-Hybrids in Electrical Biosensors.

Biosensors operating based on electrical methods are being accelerated toward rapid and efficient detection that improve the performance of the device. Continuous study in nano- and material-sciences has led to the inflection with properties of nanomaterials that fit the trend parallel to the biosensor evolution. Advancements in technology that focuses on nano-hybrid are being used to develop biosensors with better detection strategies.

Screw-Dislocation-Driven Growth Mode in Two Dimensional GaSe on GaAs(001) Substrates Grown by Molecular Beam Epitaxy.

Regardless of the dissimilarity in the crystal symmetry, the two-dimensional GaSe materials grown on GaAs(001) substrates by molecular beam epitaxy reveal a screw-dislocation-driven growth mechanism. The spiral-pyramidal structure of GaSe multi-layers was typically observed with the majority in ε-phase. Comprehensive investigations on temperature-dependent photoluminescence, Raman scattering, and X-ray diffraction indicated that the structure has been suffered an amount of strain, resulted from the screw-dislocation-driven growth mechanism as well as the stacking disorders between monolayer at the boundaries of the GaSe nanoflakes.

Monolithic 3D CMOS Using Layered Semiconductors.

Monolithic 3D integrated circuits using transition metal dichalcogenide materials and low-temperature processing are reported. A variety of digital and analog circuits are implemented on two sequentially integrated layers of devices. Inverter circuit operation at an ultralow supply voltage of 150 mV is achieved, paving the way to high-density, ultralow-voltage, and ultralow-power applications.

Efficiency improvement of InGaP/GaAs/Ge solar cells by hydrothermal-deposited ZnO nanotube structure.

In this paper, a zinc oxide (ZnO) nanotube, fabricated by the hydrothermal growth method on triple-junction (T-J) solar cell devices to enhance efficiency, is investigated. Compared to those of bare T-J solar cells (without antireflection (AR) coating) and solar cells with Si3N4 AR coatings, the experimental results show that the T-J solar cells, which use a ZnO nanotube as an AR coating, have the lowest reflectance in the short wavelength spectrum. The ZnO nanotube has the lowest light reflection among all experimental samples, especially in the range of 350 to 500 nm from ultraviolet (UV) to visible light.

Fabrication and configuration development of silicon nitride sub-wavelength structures for solar cell application.

To replace the double layer antireflection coating and improve the efficiency of solar cell, a self assembled nickel nano particle mask followed by inductively coupled plasma (ICP) ion etching method is proposed to form the sub-wavelength structures (SWS) on silicon nitride (Si3N4) antireflection coating layers instead of semiconductor layer. The size and density of nickel nano particles can be controlled by the initial thickness of nickel film that is annealed to form the nano-particles on the Si3N4 film deposited on the silicon substrate. ICP etching time is responsible for controlling the height of the fabricated Si3N4 SWS on silicon substrate, which is seen from our experiment.

Fabrication of antireflective sub-wavelength structures on silicon nitride using nano cluster mask for solar cell application.

We have developed a simple and scalable approach for fabricating sub-wavelength structures (SWS) on silicon nitride by means of self-assembled nickel nanoparticle masks and inductively coupled plasma (ICP) ion etching. Silicon nitride SWS surfaces with diameter of 160-200 nm and a height of 140-150 nm were obtained. A low reflectivity below 1% was observed over wavelength from 590 to 680 nm.