Search

ABSTRACT Compared to silicon‐based complementary metal oxide semiconductor (CMOS), second‐generation semiconductor materials, such as gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT), offer significant advantages for radio frequency (RF) applications. As communication systems become more functional, designing highly integrated on‐chip transceiver systems presents a substantial challenge, where the voltage regulator as part of the power management module is indispensable. Due to lattice defects and other issues, achieving P‐channel metal oxide semiconductor (PMOS) in GaAs pHEMT is difficult, necessitating new circuit architectures to fulfill traditional linear regulator functions. To realize wireless fidelity (WiFi) transceiver systems on chip (SoC) using compound semiconductors for superior RF performance, this paper proposes a switchable linear regulator based on a 0.25 μm GaAs pHEMT process. The proposed linear regulator consumes a quiescent current of 440 μA in no‐load conditions and regulates a 5 V supply voltage down to 2.6 V output voltage. Measured results indicate that the designed linear regulator features a current load capacity of 20 mA, a load regulation rate of 5.8 mV/mA, and a line regulation rate of 1.8 mV/V. The proposed linear regulator circuit has been applied to WiFi transceiver systems, occupying a chip area of 0.054 mm2. [ABSTRACT FROM AUTHOR]

In recent years, advances in optoelectronics and electronics have prioritized optimizing semiconductor device performance and reducing power consumption by modeling new semiconductor device geometries. One such innovative structure is the radial p-n junction structure. In this work, we present a concept that submicron three-dimensional simulations were conducted on radial p-n junction structures based on GaAs material to investigate the influence of temperature ranging from 250K to 500K with a step of 50K on the electrophysical distribution, such as space charge, electro-potential, and electric field, in radial p-n junction structures, as well as various forward voltages. In particular, we focus on the shell radius within the structure: 0.5 μm and 1 μm for the shell. The modeling results were compared with the results obtained from solving the theoretical Poisson equation in the cylindrical coordinate system.

In this paper, we present a unified model for gallium arsenide (GaAs) based on ab initio simulations which characterizes its terahertz (THz) properties when excited by optical pump. We use density functional perturbation theory to calculate the dielectric properties of GaAs, and investigate the relaxation time of photo-excited GaAs through electron–phonon interactions. In light of the complexities arising from the mixed absorption mechanisms and the sensitivity of GaAs to laser parameters, we have developed a method that leverages time-dependent density functional theory and Boltzmann transport theory. This approach enables us to establish an accurate relationship between the pump laser intensity and the carrier concentration by introducing the percentage of excited electrons, facilitating the quantitative characterization of GaAs's response under different optical pump intensities. Using the microscopic material parameters solved by first principles, we develop a unified Drude model to describe the macroscopic electromagnetic responses of photo-excited GaAs. We simulate several reported numerical examples of photo-excited GaAs, including a GaAs wafer and GaAs-based THz metamaterial modulators, to validate the proposed unified model as a reliable approach for predicting the THz properties of GaAs. The good agreement between the simulation and measurement results demonstrates that our model successfully captures the dynamic responses of photo-generated carriers and provides guidance for the design of optoelectronic devices based on GaAs. Furthermore, our modeling approach based on ab initio simulations is free from empirical parameters, providing a solid THz modeling method for other photo-excited semiconductor materials. [ABSTRACT FROM AUTHOR]

In recent years, advances in optoelectronics and electronics have prioritized optimizing semiconductor device performance and reducing power consumption by modeling new semiconductor device geometries. One such innovative structure is the radial p-n junction structure. In this work, we present a concept that submicron three-dimensional simulations were conducted on radial p-n junction structures based on GaAs material to investigate the influence of temperature ranging from 250K to 500K with a step of 50K on the electrophysical distribution, such as space charge, electro-potential, and electric field, in radial p-n junction structures, as well as various forward voltages. In particular, we focus on the shell radius within the structure: 0.5 μm and 1 μm for the shell. The modeling results were compared with the results obtained from solving the theoretical Poisson equation in the cylindrical coordinate system. [ABSTRACT FROM AUTHOR]

The present article presents critical aspects of RF system development process and its sequential phases along with associated challenges. It also discusses importance of active and passive components thermal behavior and their impact in overall system performance. The study on performance deviation of these components with temperature change has been reported. Potential issues for gain variation and frequency selectivity have been analysed and suitable solutions are explored accordingly. Implementation of temperature stabilization method in designed RF product has been carried out during prototype development. Practical achieved results are noted down during testing and measurement to monitor effectiveness of thermal stabilization mentioned in it. Finally, wideband flat gain response has been achieved by implementation of thermal stabilization for active and passive components to avoid any performance degradation. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a novel design of an X-band (812 GHz) 4-bit monolithic microwave integrated circuit (MMIC) type true-time-delay (TTD) line for wideband high-resolution imaging radar applications. The designed TTD line circuit offers a maximum time delay of 920 picoseconds (ps) using eight 115 ps delay elements and a distributed switching network. The unit delay line is synthesized using an artificial transmission line (ATL) circuit and implemented in a compact form of 18.5 mm2 using 130 nm gallium arsenide (GaAs) pseudomorphic high-electronmobility-transistor (p-HEMT) technology. The size of the switches and characteristic impedance of the transmission lines have been optimized to minimize insertion loss variation across different delay states while maintaining a flat delay response over a wide bandwidth. A basic 115 ps delay line cell is fabricated to prototype the circuit using GaAs-based MMIC processes. The final 920 ps chip layout simulation exhibited input and output return loss of better than 10 dB, insertion loss of 28±2 dB, and group delay variation of ±10 picoseconds over a 4 GHz bandwidth.

This article presents a comprehensive design framework and realization approach for a state-of-the-art, X-band 16-channel Transmit-Receive (TR) plank unit for high-resolution imaging radar applications. The Transmit-Receive Module (TRM) is the most critical component of Active Electronically Scanned Arrays (AESA), which are widely used in Radar, Electronic Warfare (EW), and Communication systems. Modern AESAs with wide instantaneous bandwidth are utilized in imaging, and high data rate communication systems require time delay lines instead of narrowband phase shifters for squint-free beam scanning over a large scan volume. The design of a compact time delay line-based TRM that fits within the inter-element spacing of AESA is quite challenging. This paper presents a novel design of a true-time-delay (TTD) line-based 16-TR Channel (TRC) plank unit as a basic building block for X-band AESA-based high-resolution Imaging Radar. A novel architecture of distributed time delay network is proposed to offer a maximum time delay of 600 ps in steps of 3.125 ps per TRC by using 6-bit TTD line core chips at the plank unit level and overall 1.4ns maximum delay at AESA level. The proposed plank unit is realized by using a multi-layer, multi-laminate printed circuit board (PCB) technology with surface-mount microwave and digital components. Automated surface mount assembly and automated test facilities are utilized to develop plank units with high repeatability and reliability. The 16-TRC plank PCB is housed in a single mechanical enclosure along with blind mate connectors for RF, digital, and power supply interfaces. Two such plank units are mounted back to back on a single liquid cold plate for efficient thermal management. This paper details the design challenges associated with packaging and thermal management of multi-TR Channel plank units in a compact size of $300\times 200$ x 8 mm3 along with RF path analysis, circuit simulation, PCB design, and proto plank unit performance characterization. The designed plank unit has demonstrated 10 Watt peak transmit output power, receive noise figure of 4 dB per TRC, and channel-to-channel isolation of 40 dB over 2 GHz bandwidth.

Summary: In this paper, a dual‐band antenna switch module with switching capability targeting the inter‐band carrier aggregation at 5G new‐radio (NR) frequency range 2 (FR2) is presented. Inter‐band carrier aggregation has become increasingly prevalent in millimeter‐wave applications at Ka‐band frequencies as a means to secure sufficient bandwidth for improving the rate of data transmission. Antenna modules with polarization switching capability are considered as a critical component for maintaining proper transmission and reception of the signals at millimeter‐wave frequencies. The integrated system consists of a wideband single‐pole‐double‐throw (SPDT) switch and a dual‐band power amplifier (PA) that are realized on the Rogers RO3010 substrate. With the two double exponentially tapered slot antennas (DETSA) arranged in the mutually orthogonal configuration, the antenna switch module can provide linear polarization at ±45 degrees. A measured error‐vector‐magnitude (EVM) of −30.3 dB at 38 GHz using 200‐MHz standard 5G NR 256‐QAM orthogonal frequency‐division multiplexing (OFDM) modulation has demonstrated the feasibility of the proposed module to be implemented for millimeter‐wave applications. [ABSTRACT FROM AUTHOR]

This paper proposes a design of a 38 GHz Low Noise Amplifier (LNA) that uses a three-stage common source inductive degeneration topology with a gain of 27 dB and noise figure of 1.78 dB using 0.1 µm GaAs pHEMT as an active device. The novelty of the design is the usage of inductive load in series with the resistor instead of resistive load, resulting in higher gain performance. A recent pp1010 active device of WIN foundry was explored for this LNA design at the Q band. The high transition frequency offered by this technology succeeded in obtaining competitive results with a minimum number of cells. The designed LNA obtained the lowest noise compared to other recently published LNA designs at the Q band. The total power consumption of this design is 57 mW. [ABSTRACT FROM AUTHOR]

This paper presents a critical and detailed overview of experimental techniques for the extraction of the thermal resistance of bipolar transistors from simple DC current/voltage measurements. More specifically, this study focuses on techniques based on a thermometer, i.e., the relation between the base-emitter voltage and the junction temperature. The theory behind the techniques is described with a unified and comprehensible nomenclature. Advantages, underlying approximations, and limitations of the methods are illustrated. The accuracy is assessed by emulating the DC measurements with PSPICE electrothermal simulations of a transistor model, applying the techniques to the simulated currents/voltages, and comparing the extracted thermal resistance data with the values obtained from the target formulation embedded in the transistor model. An InGaP/GaAs HBT and an Si/SiGe HBT for high-frequency applications are considered as case-studies. [ABSTRACT FROM AUTHOR]

This paper concerns the development of a machine learning tool to detect anomalies in the molecular structure of Gallium Arsenide. We employ a combination of a CNN and a PCA reconstruction to create the model, using real images taken with an electron microscope in training and testing. The methodology developed allows for the creation of a defect detection model, without any labeled images of defects being required for training. The model performed well on all tests under the established assumptions, allowing for reliable anomaly detection. To the best of our knowledge, such methods are not currently available in the open literature; thus, this work fills a gap in current capabilities. [ABSTRACT FROM AUTHOR]

This paper presents an optimized three-cell Nonuniform Distributed Amplifier (NUDA) suitable for optoelectronic drivers in the Q band. This is the first NUDA of Darlington topology designed with the 0.1µm GaAs pHEMT process with a transition frequency fT of 130GHz. Gate microstrip line sections, drain microstrip line sections, and active device sizes were optimized to obtain high gain and large bandwidth from a Monolithic Microwave Integrated Circuit (MMIC) Distributed Amplifier (DA). This paper presents two NUDA designs with different topologies. The first was designed with a three-stage Common Source (CS) topology that enhanced the bandwidth up to 34GHz with a gain greater than 8dB, and the second was designed with two Darlington stages and one CS stage that enhanced the bandwidth up to 38GHz with a gain greater than 8dB. The bandwidth enhancement of NUDA with the Darlington topology was compared and verified with the NUDA of common source topologies. [ABSTRACT FROM AUTHOR]

To meet the application requirements of broadband radar systems for broadband power amplifiers, a Ku-band broadband power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on a 0.15 µm gallium arsenide (GaAs) high-electron-mobility transistor (HEMT) technology is proposed in this paper. In this design, the advantages of the stacked FET structure in the broadband PA design are illustrated by theoretical derivation. The proposed PA uses a two-stage amplifier structure and a two-way power synthesis structure to achieve high-power gain and high-power design, respectively. The fabricated power amplifier was tested under continuous wave conditions, and the test results showed a peak power of 30.8 dBm at 16 GHz. At 15 to 17.5 GHz, the output power was above 30 dBm with a PAE of more than 32%. The fractional bandwidth of the 3 dB output power was 30%. The chip area was 3.3 × 1.2 mm2 and included input and output test pads. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a Doherty power amplifier (DPA) based on Class‐J power amplifier (PA) and Class‐J−1 PA is proposed for configurable Internet of things (IoT) transmitters. A post‐matching structure is used to achieve wider bandwidth performance, high efficiency, and power gain flatness. Different drain biases on the main and peaking devices are used to perform asymmetric operations. The proposed DPA structure achieves 62.4% power‐added efficiency (PAE) with a maximum output range of 37.38–38.20 dBm for the frequency band of 5.1–5.8 GHz and a power gain range of 13.24–12.24 dB. It has a maximum drain efficiency of 42.7%–51.5% at a back‐off power level of 9 dB. In order to validate the linearity of the proposed design, an analysis of the adjacent channel leakage ratio (ACLR) for various gate‐biased voltage operations is performed. The microchip occupies a compact die area of 2.1 mm × 1.2 mm, which is fabricated with GaAs 0.25 μm PHEMT to validate the enhanced broadband characteristics of the proposed configuration. Compared to the existing DPAs, the proposed DPA exhibits higher efficiency, output power, and compact size. [ABSTRACT FROM AUTHOR]

Renewable energy demand is increasing as fossil fuels are limited and pollute the environment. The solar absorber is an efficient renewable energy source that converts solar radiation into heat energy. We have proposed a gallium arsenide-backed solar absorber design made with a metamaterial resonator and SiO2 substrate. The metamaterial resonator is investigated with thin wire metamaterial and I-shaped metamaterial designs. The I-shape metamaterial design outperforms the thin wire metamaterial design and gives 96% average absorption with a peak absorption of 99.95%. Structure optimization is applied in this research paper using parametric optimization. Nonlinear parametric optimization is used because of the nonlinear system results. The optimization method is used to optimize the design and improve the efficiency of the solar absorber. The gallium arsenide and silicon dioxide thicknesses are modified to see how they affect the absorption response of the solar absorber design. The optimized parameter values for SiO2 and GaAs thicknesses are 2500 nm and 1000 nm, respectively. The effect of the change in angles is also investigated in this research. The absorption is high for such a wide angle of incidence. The angle of 30° only shows a lower absorption of about 30–50%. The effect of the change in angles is also investigated in this research. The design results are verified by presenting the E-field results for different wavelengths. The optimized solar absorber design applies to renewable energy applications. [ABSTRACT FROM AUTHOR]

Gallium (Ga) is considered a high-tech Critical Metal, used in the manufacture of several microelectronic components containing either gallium arsenide (GaAs) or gallium nitride (GaN). The current high demand for this critical metal urges the development of effective recovery processes from secondary resources such as mine tailings or electronic recycling material. The importance of bioleaching as a biotechnological process to recover metals prompted this study, where an integrative approach combining experimental and genomic analysis was undertaken to identify potential mechanisms involved in bioleaching ability and strategies to cope with high metal(loid)s concentrations in five mine isolates. The Clusters of Orthologous Group (COG) annotation showed that the "amino acid transport and metabolism" [E] was the most predominant functional category in all genomes. In addition, the KEEG pathways analysis also showed predicted genes for the biosynthetic pathways of most amino acids, indicating that amino acids could have an important role in the Ga leaching mechanism. The presence of effective resistance mechanisms to Ga and arsenic (As) was particularly important in GaAs bioleaching batch assays, and might explain the divergence in bioleaching efficiency among the bacterial strains. Rhodanobacter sp. B2A1Ga4 and Sphingomonas sp. A2-49 with higher resistance, mainly to As, were the most efficient bioleaching strains under these conditions. In bioleaching assays using cell-free spent medium Arthrobacter silviterrae A2-55 with lower As resistance outperformed all the other stains. Overall, higher efficiency in Ga leaching was obtained in bioleaching assays using GaAs when compared to GaN. [ABSTRACT FROM AUTHOR]

Gallium (Ga) is considered a high-tech Critical Metal, used in the manufacture of several microelectronic components containing either gallium arsenide (GaAs) or gallium nitride (GaN). The current high demand for this critical metal urges the development of effective recovery processes from secondary resources such as mine tailings or electronic recycling material. The importance of bioleaching as a biotechnological process to recover metals prompted this study, where an integrative approach combining experimental and genomic analysis was undertaken to identify potential mechanisms involved in bioleaching ability and strategies to cope with high metal(loid)s concentrations in five mine isolates. The Clusters of Orthologous Group (COG) annotation showed that the “amino acid transport and metabolism” [E] was the most predominant functional category in all genomes. In addition, the KEEG pathways analysis also showed predicted genes for the biosynthetic pathways of most amino acids, indicating that amino acids could have an important role in the Ga leaching mechanism. The presence of effective resistance mechanisms to Ga and arsenic (As) was particularly important in GaAs bioleaching batch assays, and might explain the divergence in bioleaching efficiency among the bacterial strains. Rhodanobacter sp. B2A1Ga4 and Sphingomonas sp. A2-49 with higher resistance, mainly to As, were the most efficient bioleaching strains under these conditions. In bioleaching assays using cell-free spent medium Arthrobacter silviterrae A2-55 with lower As resistance outperformed all the other stains. Overall, higher efficiency in Ga leaching was obtained in bioleaching assays using GaAs when compared to GaN.

To meet the application requirements of broadband radar systems for broadband power amplifiers, a Ku-band broadband power amplifier (PA) microwave monolithic integrated circuit (MMIC) based on a 0.15 µm gallium arsenide (GaAs) high-electron-mobility transistor (HEMT) technology is proposed in this paper. In this design, the advantages of the stacked FET structure in the broadband PA design are illustrated by theoretical derivation. The proposed PA uses a two-stage amplifier structure and a two-way power synthesis structure to achieve high-power gain and high-power design, respectively. The fabricated power amplifier was tested under continuous wave conditions, and the test results showed a peak power of 30.8 dBm at 16 GHz. At 15 to 17.5 GHz, the output power was above 30 dBm with a PAE of more than 32%. The fractional bandwidth of the 3 dB output power was 30%. The chip area was 3.3 × 1.2 mm2 and included input and output test pads.

This paper presents a comprehensive overview of nonlinear thermal effects in bipolar transistors under static conditions. The influence of these effects on the thermal resistance is theoretically explained and analytically modeled using the single-semiconductor assumption. A detailed review of experimental techniques to extract the thermal resistance as a function of backside temperature and/or dissipated power from DC measurements is provided; advantages, underlying approximations, and limitations of all methods are clarified, and guidelines for their correct application are given. Accurate FEM thermal simulations of an InGaP/GaAs and a Si/SiGe HBT are performed to verify the accuracy of the single-semiconductor theory. The thermal resistance formulations employed in the most popular compact bipolar transistor models for circuit simulators are investigated, and it is found that they do not properly describe nonlinear thermal effects. Alternative implementations of the more accurate single-semiconductor theory are then proposed for the future versions of the compact models. [ABSTRACT FROM AUTHOR]

This letter presents a ${K}$ -/Ka-band gallium arsenide (GaAs) low-noise amplifier (LNA) for high dynamic range (DR) radar systems. The proposed LNA adopts a two-stage topology to acquire a compact chip size and low power consumption. A feedback circuit is employed in the second stage to achieve a wideband gain response. A diode-based adaptive bias circuit is designed to simultaneously improve the linearity and maintain a low drain current. In the 3-dB bandwidth from 18.7 to 36.5 GHz, the LNA achieves a maximum small-signal gain of 15.9 dB and a minimum noise figure (NF) of 1.5 dB. The measured input 1-dB compression point (IP1dB) is higher than −1 dBm, and the measured input-referred intercept point (IIP3) is higher than 3.2 dBm in the operation band. The LNA has a chip size of 1.2 mm $\times0.8$ mm and the power consumption is 66 mW. [ABSTRACT FROM AUTHOR]

The basis of operation of modern electronics components – diodes, transistors, etc. – is the ability to control the electrical conductivity of semiconductors by doping, that is, by introducing impurities into the material. Semiconductors doped differently can be brought into contact to create junctions for controlling the direction and quantity of the current flowing through the assembly. Some examples of semiconductors are silicon (Si), germanium (Ge) and gallium arsenide (GaAs). These substances are close to insulators (intrinsic semiconductors), but the addition of a small amount of dopant leads to a strong drop in electrical resistance, turning them into conductors. Depending on the kind of dopant, n-type or p-type semiconductor can be made. Silicon is a critical element for fabricating most electronic circuits. Silicon (Si) is a pure crystalline semiconductor material; it is the well-known and most used material. After silicon (Si), gallium arsenide (GaAs) is the second most common semiconductor used in laser diodes, solar cells, microwavefrequency integrated circuits and others. This paper presents a comparison between the energy band gap Eg as a function of temperature T, energy band gap Eg as a function of doping density and intrinsic carrier density ni of silicon (Si) and gallium arsenide (GaAs) using MATLAB. [ABSTRACT FROM AUTHOR]

Gallium arsenide (GaAs) has shown potential for its wide range of applications in radio frequency integrated circuit (RF-IC) packaging due to its unique properties over the traditional Si wafers. We reported the fabrication of high-density Ag nanotwinned films deposited on (400)-oriented GaAs substrates by magnetron sputtering and electron beam evaporation. In contrast to Si, the Ti precoating on GaAs is no longer necessary to provide better adhesion of the Ag nanotwinned film on the substrates. The results indicate that both the sputtered and evaporated Ag thin films exhibit high-density columnar Ag grains vertically growing on the substrates with the coincidence site lattice (CSL)- $\Sigma 3$ twin boundaries fraction of 35.6%. The electron backscatter diffraction (EBSD) analysis reveals that the twin boundaries within the sputtered Ag columns consist of a strongly preferential orientation of (111). The successful fabrication of Ag nanotwinned film via evaporation deposition will allow the applications in the backside metallization industry to be practical. [ABSTRACT FROM AUTHOR]

Broadband and plasmonic absorbers (PAs) are key components for numerous applications in the fields of energy harvesting, thermal photonics, optoelectronic devices, and enhanced spectroscopy. In this work, we propose a simple and cost-effective metamaterial plasmonic absorber (MPA) design based on an all-dielectric GaAs pyramid nanostructure for the full solar radiation spectrum range. Simulation results demonstrate that the absorbance of the proposed MPA exceeds 85% in the full solar spectrum range, and it exceeds 90% from 0.25 μm to 3.1 μm with a relative bandwidth of approximately 170.74%, with an absorption peak up to 99% at resonance wavelength. The high absorption is attributed to the excitation of wave-guide mode, surface plasmon polariton (SPP) resonance modes combined with coupling effect and intrinsic lossy of dielectric GaAs and metallic tungsten (W). Furthermore, the proposed MPA is polarization-independent and wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. Additionally, the MPA can tolerate certain structural parameter errors during practical fabrication applications. Furthermore, the photophysical properties of this MPA for solar cell applications are investigated, revealing the achievement of high short-circuit current density. Our proposed design is highly promising for applications in solar energy harvesting, thermoelectric, and thermal emitter applications. [ABSTRACT FROM AUTHOR]

The investigation of nonlinear transient characteristics of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSS) is of great significance for its applications in pulsed power technology. In this letter, the laser diode (LD) energy of $2~\mu \text{J}$ is employed to trigger the opposed-electrode GaAs PCSS. The compressed pulse width and increased amplitude are obtained as the bias electric field increases from 6kV/cm to 34kV/cm. It is numerically modeled the transient electric field distribution along the photogenerated carriers’ transport. Results reveal that pulse compression effect (PCE) can be attributed to the negative differential mobility (NDM) and electric-field screening (EFS) effect. The compression of pulse width on time scale provides a possibility to relieve the heat accumulation on time scale, and further to suppress the device failure for the potential high-repetition-rate applications. [ABSTRACT FROM AUTHOR]

The epitaxial lift-off (ELO) process based on selectively etching a thin sacrificial AlAs layer from GaAs substrate was performed using high-concentrated aqueous hydrofluoric (HF) etchant. However, because of using the wet etching method, the traditional ELO process has many drawbacks and limitations. Supercritical fluids (SCFs) naturally have the characteristics of low viscosity, high diffusivity, and zero surface tension. Therefore, the development of a gas-phase-like dry etching method based on mixing HF into CO2 and operating the mixture of HF/CO2 in SCFs condition as etchant is hereby proposed to overcome those bottlenecks existing in traditional wet ELO processes. However, there are no available experimental results for etching AlAs layers by HF in SCFs yet. Therefore, a HF-compatible corrosion-resistant high-pressure system was designed and built up to perform the idea. The capabilities of etching sample in supercritical CO2 (scCO 2) had been systemically investigated under various pressures (2000–3000 psi) and temperatures (40–60 ∘ C). Besides, the etching performances separately conducted by using aqueous-HF and anhydrous HF/Pyridine as the source etchant and mixing with scCO2 at a fixed temperature, pressure and etching time were also examined and compared under different equivalent HF concentrations. An evaluation of using acetone as the co-solvent mixed with HF/scCO2 mixture for enhancing the etch rate in different volume ratio of HF/co-solvent was further investigated and discussed. With this system, we demonstrate releasing a size of 2 0 mm × 2 0 mm (width × length) and 3  μ m-thick free-standing GaAs sheet from a 150 nm AlAs sacrificial layer by the etching sample in HF/scCO2 mixture. The released GaAs sheet was also successfully transferred to a flexible PET substrate by using a PDMS stamp and an adhesive layer of NOA61. [ABSTRACT FROM AUTHOR]

In this article, the analysis, design, and development of a 37-GHz asymmetric Doherty power amplifier (DPA) are presented. In a practical DPA, the main power amplifier (PA) shows nonideal characteristic, which varies the effect of the load modulation. Based on the theoretical analysis, we derive the relationship among the efficiency, power back-off (PBO) level, and the corresponding load impedance in a nonideal load modulation. The result suggests that a Class-AB main PA shows a decreased PBO efficiency during the load modulation. To achieve a good compromise between PBO level and PBO efficiency of the main PA, the load modulation scheme is redesigned in this work. A 2-dB PBO of the main PA is chosen to maintain the high efficiency during the load modulation. An asymmetric DPA topology is employed to compensate the inadequate PBO of the main PA so that a desired 6-dB PBO is achieved. Generally, the RF leakage at the DPA output degrades its performance. To solve this issue, we propose a modified low characteristic impedance DPA output network. The output matching network of the auxiliary PA is particularly designed to enlarge its output impedance. Through these design techniques, the leakage loss is significantly reduced to 0.2 dB, which improves the gain and power-added efficiency (PAE) at PBO. To validate the proposed techniques, a DPA chip is designed and fabricated in a D-mode 0.1- $\mu \text{m}$ GaAs pHEMT process. At 37 GHz, the 1.6 mm $\times1.8$ mm integrated chip exhibits a measured small-signal gain of 15.6 dB and a saturated power ($P_{\mathrm{sat}}$) of 28.0 dBm, with an associated 33.2% peak PAE and a 32.0% PAE at 6-dB PBO. To the best of our knowledge, the proposed chip exhibits the state-of-the-art overall performance among DPAs operating around 37 GHz for 5G n260 millimeter-wave (mm-wave) band. [ABSTRACT FROM AUTHOR]

This work presents the design and characterization of an ultralow-power core chip for electronically scanned arrays at $X$ -band, implemented in 0.25-/0.5- ${\mu }\text{m}$ E-/D-mode gallium arsenide (GaAs) pHEMT technology. In particular, design details are given about the two core functional blocks embedded in the microwave monolithic integrated circuit (MMIC): a 12-bit phase and amplitude control circuit and an 18-bit serial-to-parallel (S2P) interface. The S2P interface was designed resorting to a custom symmetric device model, expressly conceived for the time-domain simulations required for digital circuits. Due to the adoption of a differential structure with resistive pull-ups, it achieves a state-of-the-art power consumption of 2.2 mW/bit and nearly 87% yield. The analog circuit includes a 6-bit phase shifter (PS) and a 6-bit attenuator. To mitigate risks, two different PS architectures have been developed and are compared in this work, discussing advantages and drawbacks of the different solutions. Since the two designs share the same target specifications, a truly fair comparison can be made not only in terms of performance but also concerning robustness and repeatability, thus providing useful guidelines for the selection of the most appropriate strategy. In particular, it is shown that one architecture outperforms the other by about 2 dB and 1.5° in terms of insertion loss and rms phase error, respectively. [ABSTRACT FROM AUTHOR]

A comparative study of the anodization processes occurring at the GaAs(111)A and GaAs(111)B surfaces exposed to electrochemical etching in neutral NaCl and acidic HNO3 aqueous electrolytes is performed in galvanostatic and potentiostatic anodization modes. Anodization in NaCl electrolytes was found to result in the formation of porous structures with porosity controlled either by current under the galvanostatic anodization, or by the potential under the potentiostatic anodization. Possibilities to produce multilayer porous structures are demonstrated. At the same time, one-step anodization in a HNO3 electrolyte is shown to lead to the formation of GaAs triangular shape nanowires with high aspect ratio (400 nm in diameter and 100 µm in length). The new data are compared to those previously obtained through anodizing GaAs(100) wafers in alkaline KOH electrolyte. An IR photodetector based on the GaAs nanowires is demonstrated.

This article presents an X/Ku dual-band switch-free reconfigurable GaAs low-noise amplifier (LNA) realized by inter-stage and output-stage coupled lines. This article is the first switch-free reconfigurable LNA design in the coupled lines structure. After amplified by the broadband drive stage, the input signal is divided into two parallel single-band stages (consists of a high-band stage and a low-band stage) by the proposed inter-stage coupled line. Two split-band signals are combined by the proposed output-stage coupled line into the output port after amplified by the single-band stages. The proposed coupled lines are also included in LNA matching networks. Dual-band operation of the proposed reconfigurable LNA is achieved by turning off drain voltages of the unused single-band transistors. The reconfigurable LNA is designed in a 0.15-μm E-mode GaAs pHEMT process. The fabricated LNA features small-signal gains of 25-25.2/20.1-28 dB, noise figure (NF) of 1.28-1.41/1.23-1.51 dB, and output 1-dB compression point of 0.5-1.7/2.2-5 dBm over 8-10/12-20 GHz, while consuming 76/91 mA of dc current, with a size of 2.0 × 1.8 mm2.

The spectral response mechanism associated with the thickness of the absorbing layer (hAbs) in Gallium Arsenide (GaAs)-based blocked-impurity-band (BIB) far-infrared detectors have been investigated. It is found that Spectral bandwidth is approximately a linearly increasing function of hAbs. Our results reveal that the dependence of spectral bandwidth on hAbs is contrary to that of response bandwidth on hAbs, and thus the optimal hAbs exists due to the tradeoff between the spectral bandwidth and the response bandwidth. In our analysis, we define the bandwidth figure of merit (BWFOM) of GaAs-based BIB detector as the spectral bandwidth multiplied by the n power of the response bandwidth. It is demonstrated that the optimal hAbs corresponding the maximum BWFOM is about 35.4 μm. When BWFOM is less than 35.4 μm, the BWFOM is dominated by the spectral bandwidth. However, when BWFOM is larger than 35.4 μm, the BWFOM is dominated by the response bandwidth. [ABSTRACT FROM AUTHOR]

A miniaturized Ka-band bandpass filter (BPF) is presented by using monolithic microwave integrated circuit (MMIC) technology in this brief. Aiming at low cost and high integration, small die area of MMIC BPFs is significantly required for RF front-end modules.However, the filtering performance of BPFs is negatively correlated to its miniaturization. To this end, the folded hybrid resonator is investigated in this brief, which is composed of a quasi-lumped capacitor and a distributed microstrip line. To realize miniaturization, two metal layers of GaAs process are fully utilized. For low loss, the distributed inductor is designed on the top thick layer, while the quasi-lumped capacitor is on the lower metal layer of high sheet resistance. To reduce the unwanted mutual coupling between adjacent quasi-lumped capacitors, shielding structures are added into BPFs, resulting in a 5-dB and 12-dB enhancement to the lower and upper stopbands, respectively. Based on the mixed electric-magnetic coupling topology, a second-order MMIC bandpass filter is designed and fabricated by using GaAs process. Small die area, low loss, high selectivity, and wide stopband are simultaneously obtained, indicating a promising application of the proposed miniaturized MMIC bandpass filters. [ABSTRACT FROM AUTHOR]

This paper explores the efficacy of base ballasting strategies in enhancing the electrothermal (ET) stability of paralleled InGaP/GaAs heterojunction bipolar transistors (HBTs) for radiofrequency (RF) applications. More specifically, technologically-feasible temperature-dependent base ballasting resistors are proposed as a solution to shift the collapse of current gain to higher power densities. A three-cell test device fabricated through a state-of-the-art process is considered as a simple case study. Extremely accurate DC and AC ET simulations are performed with SPICE to quantify the advantages of the proposed strategy with respect to traditional approaches. • Base ballasting resistors help improve HBT safe-operating areas and mitigate ET instabilities. • On the other hand, they can be detrimental for HBTs RF performances. • An innovative ballasting strategy is proposed relying on temperature-dependent base ballasting resistors. • Extremely accurate ET simulations are performed to quantify the advantages of such a strategy. [ABSTRACT FROM AUTHOR]

This paper presents highly selective, low-loss, and miniaturized balun devices fabricated using the integrated passive device (IPD) technique for the GSM band (900/1800 MHz) and the WiFi band (2400 MHz) in mobile applications. Balun devices were fabricated on a gallium arsenide (GaAs) substrate using the IPD fabrication process to reduce the overall size (0.05λg × 0.036λg at 900 MHz). Each device is the combination of lattice lumped structure with a low-pass filter and a high-pass filter configuration. This structural formation of lumped elements helps to reduce the phase mismatch error in the balun devices. For all the balun devices, the measured results indicated a minimum amplitude imbalance (

Employing sunlight to produce electrical energy has been demonstrated to be one of the most promising solutions to the world’s energy crisis. The device to convert solar energy to electrical energy, a solar cell, must be reliable and cost-effective to compete with traditional resources. This paper reviews many basics of photovoltaic (PV) cells, such as the working principle of the PV cell, main physical properties of PV cell materials, the significance of gallium arsenide (GaAs) thin films in solar technology, their prospects, and some mathematical analysis of p-n junction solar cells. Furthermore, the paper presents the standard model of solar cells with the application of this model to different PV technologies together with the main findings. Moreover, the paper explores the role of numerical and mathematical modelling of PV cells by MATLAB/Simulink and COMSOL in evaluating the power conversion efficiency (PCE) of the PV cells and determining the main parameters affecting the power output at various conditions.

This paper presents a comprehensive overview of nonlinear thermal effects in bipolar transistors under static conditions. The influence of these effects on the thermal resistance is theoretically explained and analytically modeled using the single-semiconductor assumption. A detailed review of experimental techniques to extract the thermal resistance as a function of backside temperature and/or dissipated power from DC measurements is provided; advantages, underlying approximations, and limitations of all methods are clarified, and guidelines for their correct application are given. Accurate FEM thermal simulations of an InGaP/GaAs and a Si/SiGe HBT are performed to verify the accuracy of the single-semiconductor theory. The thermal resistance formulations employed in the most popular compact bipolar transistor models for circuit simulators are investigated, and it is found that they do not properly describe nonlinear thermal effects. Alternative implementations of the more accurate single-semiconductor theory are then proposed for the future versions of the compact models.

The transient performance of gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) triggered by laser diodes (LDs) at nano-joules (nJ) energy is of great significance for the potential high-power applications at high repetition rates. An opposed-contact GaAs PCSS with Ni/AuGe/WTi/Au electrodes is presented at single-shot and 1-kHz excitation. The influences of bias electric field up to 80 kV/cm on nonlinear characteristics are investigated quantitatively with a carriers’ avalanche multiplication factor as high as 0.8 ×104. The effect of electric field on the carriers’ dynamic process and thermal accumulation in repetitive operation is analyzed. The transient electric field distribution is demonstrated by an ensemble Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

The formation of avalanche charge domain in high-power GaAs device has been studied numerically. According to the numerical simulation results of the distribution of electric field in the bulk of the device, the variation rules of peak electric field within the domain and the domain width with the bias electric field, the carrier concentration, and the device length are obtained, respectively, and by the comparison of the variation rules with and without considering carrier impact ionization, the effect of the carrier impact ionization on the peak electric field and the domain width have been obtained. It shows that 1) the peak electric field is mainly determined by the bias electric field, the carrier concentration and the device length, and the domain width is mainly determined by the carrier concentration and the device length; 2) the carrier impact ionization and avalanche multiplication have a significant effect on the peak electric field and domain width; and 3) the value of the peak electric field and domain width are closely related to the position of domain in the direction of domain motion. Based on the variation of peak electric field and domain width, the formation of avalanche charge domain is discussed. Our results can deepen the understanding of breakover mechanism of GaAs devices and contribute to the optimization of GaAs devices performance. [ABSTRACT FROM AUTHOR]

Carrier transport mechanism associated with the thickness of the absorbing layer in GaAs-based blocked-impurity-band (BIB) far-infrared detector has been investigated in detail. It is found that responsivity linearly increases with the increased thickness of absorbing layer first, and after achieving a peak value, and then starts dropping slowly. In order to explore the carrier transport mechanism behind the phenomena, the physical meaning of responsivity has been illuminated first, and then the vertical profiles of the optical generation rate, the electric field intensity, and the carrier mobility have been obtained, respectively. It is demonstrated that the carrier transport mechanism associated with the thickness of the absorbing layer can be attributed to the competing effects of the optical generation rate, the electric field intensity, and the carrier mobility. [ABSTRACT FROM AUTHOR]

In this letter, a millimeter-wave (mm-wave) dual-band bandpass filter is proposed with large bandwidth ratio by using gallium arsenide (GaAs)-based integrated passive device (IPD) technology. To realize small chip size, one dual-mode on-chip resonator is designed by using quasi-lumped capacitors and microstrip lines. In addition, multiple transmission zeroes are generated by further introducing both the electric and magnetic couplings between adjacent resonators. To realize large bandwidth ratio of two passbands, the external quality factors are investigated at both passband, and can be independently controlled. For demonstration, a 28-/50-GHz dual-band bandpass filter is designed, fabricated, and measured. The fractional bandwidth ratio is 7.8, which is much larger than the reported on-chip filters. Meanwhile, very low insertion loss of 0.58-dB is realized for the lower passband at 28 GHz, indicating the proposed dual-band bandpass filter a promising application in mm-wave wireless systems. [ABSTRACT FROM AUTHOR]

This letter presents a multiband switchable low-noise amplifier (LNA) in the 0.1- $\mu \text{m}$ GaAs pHEMT process. Employing a new varactor-based tunable network as the interstage matching circuit, the operation bands can be tuned consecutively and cover the 5G millimeter-wave frequency bands N257/N260. The proposed tunable structure functions well without sacrificing noise performance or increasing dc consumption and chip area. In the entire operation band from 26.5 to 41 GHz, the LNA achieves a small-signal gain of over 24 dB and a noise figure (NF) of less than 2.9 dB. The measured result shows a small-signal gain of 25.1 dB/27.7 dB and an NF of 2.4 dB/2.8 dB at 28 GHz/39 GHz. The measured input 1-dB compression point (IP1dB) is −18.3 dBm/−17 dBm at 28 GHz/39 GHz. The measured input-referred intercept point (IIP3) is −8.8 dBm/−8.5 dBm at 28 GHz/39 GHz. The LNA has a chip size of 1.6 mm × 1 mm, and the total power consumption is 74 mW. To the best of our knowledge, the proposed LNA is the state-of-the-art Ka-band switchable LNA and has similar performance compared with single-band LNAs using the same technology. [ABSTRACT FROM AUTHOR]

Millimeter-wave (mm-wave) monolithic-microwave-integrated-circuit (MMIC) bandpass filters (BPFs) usually feature high insertion loss (IL). To this concern, an analytical method for low-loss MMIC BPFs is presented by using lumped-distributed parameters in this article. To reduce the IL, the enhanced-quality-factor resonator and low-loss coupling topology are both investigated. First, the proposed resonator and filter are realized by combining quasi-lumped elements and distributed mutual coupling. Both compact size and multiple transmission zeroes are accordingly realized. Second, a low-loss coupling topology is further introduced for MMIC filter by using mixed electric and magnetic couplings. For theoretical analysis, the lossy equivalent circuit modeling for mm-wave MMIC BPF is investigated, as well as an analytical parameter extraction. Based on the circuit analysis, a fast synthesis of low-loss mm-wave MMIC filter is presented. For demonstration, two compact MMIC BPFs are designed by using the gallium arsenide (GaAs) process. Low IL of only 0.95 dB, sharp rejection skirt of passband, and wide stopband are simultaneously obtained. The features of the proposed MMIC BPFs indicate promising applications in the fifth-generation (5G) mm-wave systems. [ABSTRACT FROM AUTHOR]

This work focuses on the design issues of radio frequency (RF) bipolar integrated circuits (ICs) as a part of frequency synthesizers for extreme environmental applications. It is shown that silicon–germanium (SiGe) and gallium arsenide (GaAs) heterojunction bipolar transistors (HBTs) as well as bipolar RF ICs (including frequency dividers, voltage-controlled oscillators, and wide-band amplifiers) are highly sensitive to ambient temperature and radiation-induced displacement damage. This article also presents a design approach based on specialized HBT macromodels and hardening techniques. [ABSTRACT FROM AUTHOR]

This article presents a frequency-reconfigurable outphasing GaAs power amplifier MMIC operating over an 18–38-GHz range with 2–6-GHz RF bandwidth per frequency setting. The architecture is based on a broadband power combining structure providing nonisolating power combining. Reconfigurable shunt elements based on p-i-n diode switches control the Chireix reactance compensation to enable frequency-reconfigurable efficiency enhancement at output power back-off (OBO). The prototype two-stage MMIC is characterized under CW and modulated measurements demonstrating 20–24-dBm saturated output power over the band 18–38 GHz, with measured PAE of 23%–31% at peak and 17%–23% at 6-dB OBO. When measured with a 200-MHz LTE signal with 9-dB PAPR centered at 19.5 GHz, the PA performs with 15.3% average efficiency at a 14.3-dBm average output power with 24.18-dBc ACLR. [ABSTRACT FROM AUTHOR]

This paper comes with a new study on the design of a microstrip broadband power amplifier suitable for ISM (Industrial, Scientific and Medical) band. The broadband PA design is based on the balanced amplifier topology, using the hybrid coupler and advanced GaAs FET transistor technology in order to produce a good broadband performance on all the critical parameters. By utilizing the balanced amplifier design topology, the circuit yields excellent linearity and low return loss over a broad-bandwidth. And by using the hybrid coupler in the balanced amplifier topology reduces the size compared to conventional balanced PA topology. The broadband power amplifier was designed on an Epoxy (FR4) substrate and exhibits a power gain greater than 17dB, a saturated output power of 17dBm at 1dB compression point and return loss (input and output) less than -15dB across the broadband frequency range from 2.4-2.5GHz. [ABSTRACT FROM AUTHOR]

Terahertz (THz) photodetector has attracted great attention from worldwide scientists for its applications in security check, biomedical treatment, and astronomical observation. In the performance evaluation of the THz photodetector, the noise level is one of the critical parameters. The Gallium Arsenide (GaAs) blocked-impurity-band (BIB) detector, which is fabricated from intrinsic GaAs-based photoconductive detectors, reveals an attractive advantage of low dark current value and high signal to noise ratio (SNR). In this work, the epitaxial GaAs BIB detector was fabricated and its noise behavior under various bias was investigated at the temperature of 3.5 K. The measured noise consists of flicker noise (1/f noise), shot noise, thermal noise and measurement noise. The effect of bias and operation temperature (TOpe) on the noise characteristics of a GaAs-based BIB detector has been studied by numerical simulation for suppressing device noise. According to the simulation, the total noise gradually increases with TOpe, and dominated by the shot noise. Our work may provide useful theoretical support to solve the critical epitaxial growth bottleneck of GaAs BIB detector and improve its performance for the applications of astronomical observation, security check, etc. [ABSTRACT FROM AUTHOR]

• A GaAs vertical-tunnel-junction (VTJ) cell is evaluated up to 10,000 suns. • The VTJ is optimised and the effect of the recombination processes investigated. • The electrical parameters are not limited by the recombination and concentration. • A linear increase of the efficiency of the VTJ with concentration is found. • A maximum efficiency of 32.2% at 10,000 suns was obtained. Ultra-high concentrator photovoltaic systems (UHCPV), usually referred to CPV systems exceeding 1000 suns, are signalled as one of the most promising research avenues to produce a new generation of high-efficiency and low-cost CPV systems. However, the structure of current concentrator solar cells prevents their development due to the unavoidable series resistance losses at such elevated concentration ratios. In this work, we investigate the performance of the so-called vertical-tunnel-junction (VTJ), recently introduced by the authors, by using advance TCAD. In particular, we carry out an optimisation procedure of the key parameters that affect its performance and conduct a deep investigation of the impact of the main recombination mechanisms and of sun concentration up to 10,000 suns. The results indicate that the performance of the novel structure is not significantly affected by these two factors. A record efficiency of 32.2% at 10,000 suns has been found. This represents a promising way to obtain state-of-the-art efficiencies above 30% for single-band-gap cells, and offers a new route towards the development of competitive CPV systems operating at ultra-high concentration fluxes. [ABSTRACT FROM AUTHOR]