High-power FET Research Articles

Thermal Surface Interface for High-Power Arsenide–Gallium Heterostructure FETs

Application of heat-conducting coatings for cooling of high-power FETs based on heterostructures with arsenide–gallium substrate is theoretically analyzed. When the basic technology for manufacturing of transistors is employed in the absence of additional efforts aimed at a decrease in the thermal resistance of the substrate, the application of an additional thermal interface that represents a heat-conducting dielectric coating makes it possible to substantially decrease the overheating of the transistor channel. A several-fold decrease in such overheating can be reached using variations in the thickness of the coating and modification of the transistor structure and working regimes.

Поверхностный тепловой интерфейс для мощных арсенид-галлиевых гетероструктурных полевых транзисторов

AbstractApplication of heat-conducting coatings for cooling of high-power FETs based on heterostructures with arsenide–gallium substrate is theoretically analyzed. When the basic technology for manufacturing of transistors is employed in the absence of additional efforts aimed at a decrease in the thermal resistance of the substrate, the application of an additional thermal interface that represents a heat-conducting dielectric coating makes it possible to substantially decrease the overheating of the transistor channel. A several-fold decrease in such overheating can be reached using variations in the thickness of the coating and modification of the transistor structure and working regimes.

Study of non-linear optical properties of center and edge delta-doped multiple quantum wells

In the present paper, the linear and non-linear optical properties of GaAs/AlGaAs multiple quantum well with on-center and on-edge delta doping are studied within the effective mass approximation. The delta potential is analytically modeled within each quantum well potential to obtain the energy levels and the corresponding wave functions using the robust finite difference method. The linear and non-linear optical absorption coefficients and changes in the refractive index are studied in the presence of a static magnetic and a periodic laser field using the density matrix approach. The obtained results show that the position of resonances and the amplitude of the optical absorption coefficients and the refractive index changes can be modified by varying the magnetic field and strength and position of doping potential. Lastly, an increase of the optical intensity appreciably changes the total absorption coefficient, as well as the total refractive index changes. Obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices based on the intersubband transition of electrons in δ-doped multiple quantum wells.

(Invited) Electrochemical Formation and Application of Porous Gallium Nitride

Gallium nitride (GaN), which is a III-V compound semiconductor, has wide direct bandgap (3.4 eV), high breakdown electric field (3.3x106 V/cm) and high saturation electron velocity (2.7 x107 cm/sec). On the basis of excellent optical and electrical properties, significant progress has been achieved in the GaN-based devices, such as ultraviolet laser diodes, white light-emitting diodes, high electron mobility transistors (HEMTs), and high-power FETs. In addition, GaN and its alloys are getting much attention as building block materials for electrochemical (EC) energy conversion systems such as chemical sensors, water splitting, and artificial photosynthesis due to their superior chemical stability, direct transition, and widely tunable bandgap by alloying. Among the various techniques for improving their conversion efficiency, porosification utilizing EC reactions is one of the most powerful because a high-density array of pores exhibits high specific surface area, low reflectance, and high absorptance properties. In addition, this technique is performed at room temperature and does not require any complicated process such as lithography, indicating lower damage and higher productivity than other nanostructure fabrication techniques such as reactive ion etching and selective-area growth. In this presentation, we review our recent work on the fabrication of porous GaN utilizing various EC techniques and their applications [1-3]. One example is the two-step process combining EC etching process with conventional chemical etching process. EC etching was first performed in the dark condition using an aqueous electrolyte consisting of H2SO4 and H3PO4. Wet chemical etching was subsequently conducted in 25 % tetramethylammonium hydroxide (TMAH) at 90°C. The porous structure formed by the first EC etching has straight pores oriented perpendicular to the top surface. Pore depth linearly increased with EC etching time, indicating that superior depth control was achieved. This behavior can be explained as resulting from anisotropy of the EC etching. Namely, the etching reaction proceeded only to the direction belong to the high-electric field induced by the anodic voltage. On the other hand, the pore diameter kept a constant value throughout the EC etching and could not be controlled by the EC etching time. However, the pore diameter could be changed by wet chemical etching utilizing TMAH as subsequent treatment after the EC etching. By applying TMAH etching, pore shape changed from a round to a hexagonal shape surrounded with 6 facets of {1−100}. In addition, the pore diameter estimated from SEM observation increased linearly with the TMAH etching time, whereas the pore depth was unchanged. These results indicate that TMAH etching proceeds anisotropically in the horizontal direction, but not in the vertical direction of the substrate. The optical and photoelectrochemical properties of porous GaN were very sensitive to the structural properties. From the photoluminescence (PL) measurements, the intensity of yellow luminescence (YL) related to high-density point defects was drastically decreased by the formation of porous structures, suggesting that gallium vacancy (V Ga) related defects were preferentially removed by EC etching. Photoreflectance measurement revealed that porous sample had an effective refractive index that could be controlled by TMAH etching time. In photoelectrochemical measurement, the incident-photon-to-current conversion efficiency (IPCE) was dramatically enhanced by the formation of porous structures. A series of experimental results were consistently explained by the change of thickness of pore wall with a width of space charge region. These results suggest that precise structural controlling is crucially important to obtain superior capability for EC energy conversion systems, and the two-step process utilizing anisotropic EC etching and TMAH etching is very promising as a nanostructure fabrication technique. Acknowledgement: This work was supported by JSPS KAKENHI - JP15K13937，JP16H06421，JP17H03224. A. Watanabe et al., ECS Electrochem. Lett., 4, H11 (2015).Y. Kumazaki et al., J. Electrochem. Soc., 164, H477 (2017).M. Toguchi et al., 233rd ECS Meeting, Z01-2550, Seattle, WA, 15 May (2018).

Effect of Si δ-Doping on the Linear and Nonlinear Optical Absorptions and Refractive Index Changes in InAlN/GaN Single Quantum Wells**Supported by the Deanship of Scientific Research of University of Dammam under Grant No 2015134.

In the framework of effective mass approximation, we theoretically investigate the electronic structure of the Si δ-doped InAlN/GaN single quantum well by solving numerically the coupled equations Schrödinger–Poisson self-consistently. The linear, nonlinear optical absorption coefficients and relative refractive index changes are calculated as functions of the doping concentration and its thickness. The obtained results show that the position and the amplitude of the linear and total optical absorption coefficients and the refractive index changes can be modified by varying the doping concentration and its thickness. In addition, it is found that the maximum of the optical absorption can be red-shifted or blue-shifted by varying the doping concentration. The obtained results are important for the design of various electronic components such as high-power FETs and infrared photonic devices.

PECVD and Thermal Gate Oxides on 3C Vs. 4H SiC – Impact on Traps, Leakage and Energy Offsets

Silicon carbide (SiC) is particularly suitable for manufacturing of medium and high power FETs. Two SiC polytypes most commonly used for that purpose, i.e. cubic 3C and hexagonal 4H, differ, however, in many aspects, which influence the operation of the devices. The differences in interface trap distributions, gate leakage and energy band model offsets resulting from the SiC polytypes were investigated in this work. Samples. Characterized were two lots of wafers (3C-SiC and 4H-SiC) fabricated by Acreo AB. The 3C-SiC lot consisted of two n-type (001) 3C-SiC wafers. The substrates from Hoya were covered at Acreo by a n-type epitaxial layer with nitrogen doping of 7×1015 cm-3. One wafer was thermally oxidized in wet oxygen (T = 1150°C, 1h) while the other had the SiO2 layer deposited by PECVD at T = 300°C. This second wafer was further annealed for 3 hours in wet oxygen at T = 950°C. The oxide thickness on both wafers was 60 nm.The 4H-SiC lot consisted of two SiC-4H n-type wafers, one with a thermal (53 nm) and another with a PECVD (45 nm) gate oxide fabricated in the processes analogical to the 3C-SiC lot. Measurements.The gate leakage currents were measured on Agilent B1500AB. The interface trap distributions were measured by standard conductance method on Agilent 4294A. The energy band model offsets were established using our own specialized equipment for photoelectric measurements. The methods used were discussed in details in [1,2,3]. Results. The important difference between the 3C and 4H polytypes is the width of the energy gap: EG(3C)=2.36 eV and EG(4H)=3.23 eV [4]. In Fig. 1 the trap density distributions measured in the samples in both polytypes are presented. The energy axis shows the trap distance from the top of the valence band EV, what enables the comparison of Dit in both systems. As expected, the Dit values in 4H-SiC are higher than those in 3C-SiC, irrespective of the oxide preparation method, due to the presence of a band of interface traps in the oxide, so called NIT (near-interface traps), caused probably by oxygen vacancy defects (O3ΞSiH HSiΞO3) producing trapping states at 3.0 eV...3.2 eV above EV, as reported by Afanas’ev [4] and others [5].An interesting feature can be demonstrated comparing gate leakage currents. In Fig. 2 we present the averaged leakage current density characteristics measured in both polytype samples. One can notice a very small difference in the leakage current density J between the oxides, while the difference with respect to the substrate polytype is very large. The density of leakage currents in 4H is by two orders of magnitude lower than that in 3C. Since the oxide preparation procedure in both samples was identical, the difference could not be explained by the oxide properties only. We presume that the mechanism of the increased leakage in the 3C-SiC is connected with trap enhanced tunneling from the conductance band by the NIT defects.Finally we present the most important 3C- and 4H-SiC MOSC energy-band model offsets shown in Fig. 3. The offset values are given in Tab. 1. All the values were taken for PECVD oxide and Al gate. Conclusions Energy-band model offsets, trap density distributions and gate leakage characteristics of MOS capacitors with PECVD and thermal gate oxide on 3C- and 4H-SiC were compared. The important role of NIT traps in both polytypes influencing different device characteristics was demonstrated.

Improvement Hardware Design of High Power and Ultra-Low Frequency Signal Source in Cased Hole Resitivity Logging

The cased hole resistivity logging technology is one of high-tech logging technologies being studied in China. The signal source requires high voltage, high current, ultra-low frequency, high stability, high resolution, etc. Based on the characteristics, proposed were the ideas that the direct digital synthesis technique should be applied to produce the required sine logging exciting signals, and high-power FET were used to produce the signals with high power and high voltage. The results show that the output frequency of signal source is 0~ 10 Hz, frequency resolution 0. 002 Hz, output voltage range -300 V~+300V, output current less than 6 A. The design has been successfully applied in the research project of extremely weak nV-level electric signal acquisition theory and experimental study on formation resistivity measurement through metal casing.

Passivation of H‐terminated diamond with MOCVD‐aluminium nitride – a key to understand and stabilize its surface conductivity

AbstractThe surface conductivity of hydrogen (H)‐terminated diamond still suffers from instabilities at high temperature especially in O‐containing atmosphere and/or under high power FET device operation. For devices based on this H‐induced surface conductivity concept, stabilization is thus essential. In this investigation AlN, deposited by MOCVD at 800 °C, has been used as passivation and gate dielectric in Surface Channel MESFET and MISFET structures. Despite the high deposition temperature, the H‐induced channel is still present in the case of both structures and can be fully modulated. Surface Channel MESFETs yield a maximum output current density of 200 mA/mm (at pS = 9.5 × 1012 cm−2) in enhancement mode of operation. MISFETs display 20 mA/mm current density (at pS = 2.1 × 1012 cm−2) in semi‐enhancement mode of operation, the maximum current being limited by AlN dielectric breakdown. The film shows strong adhesion. To explain all features consistently, it is proposed that the interfacial bonding is provided by a H‐double bond.

X-ray characterization of GaN single crystal layers grown by the ammonothermal technique on HVPE GaN seeds and by the sublimation technique on sapphire seeds

ABSTRACTSingle crystal GaN substrates are a more reliable, efficient and low cost alternative to sapphire and SiC substrates that are currently being used for developing nitride based devices such as LEDs, high power FETs and laser diodes. GaN growth by two techniques are investigated here. In ammonothermal growth (analogous to hydrothermal growth which is commonly used for quartz), using potassium and lithium amide as mineralizers and GaN powders and vapor grown polycrystals as nutrients, thick GaN single crystal layers have been grown on both faces of (0001) HVPE GaN seeds in nickel based autoclaves. In GaN sublimation growth, Ga is transported under a temperature gradient in an ammonia atmosphere from a GaN powder source to the sapphire substrate which has a 3–6 micron GaN epilayer deposited on it. Synchrotron white beam x-ray topography (SWBXT) was initially used to image the defect structures in the layers. High resolution x-ray diffraction experiments were also carried out and reciprocal space maps were recorded from the grown GaN layers. Characterization results will be discussed with respect to the growth conditions.

Synchrotron white beam x-ray topography (SWBXT) and high resolution triple axis diffraction studies on AlN layers grown on 4H- and 6H-SiC seeds

ABSTRACTFor nitride based devices such as LEDs, high power FETs and laser diodes, single crystal substrates of AlN are highly desirable. While the sublimation technique is suitable for growing bulk AlN crystals, appropriate seeds are also necessary for growing large diameter oriented boules. 4H- and 6H-SiC substrates which are readily available commercially can potentially be implemented as seeds for bulk AlN growth. However, issues regarding SiC decomposition at high temperatures, thermal expansion mismatch, single crystal growth, etc. need to be addressed. Towards this end, a series of growth experiments have been carried out in a resistively heated reactor using on and off-axis 4H- and 6H-SiC substrates as seeds for AlN growth from the vapor phase. Several hundred microns thick AlN layers have been grown under different growth conditions. Synchrotron white beam x-ray topography (SWBXT) has been used to map the defect distribution in the grown layers and high resolution triple axis x-ray diffraction (HRTXD) experiments were carried out to record reciprocal space maps from which tilt, mismatch and strain data can be obtained. These results are analyzed with respect to the growth conditions in order to gain a better understanding of this growth process.

AlGaN/GaN FETs looms over GaAs technology

In spite of deep concerns about the spread of severe acute respiratory syndrome in Asia, the 5th International Conference on Nitride Semiconductors at Nara was well attended with 442 presentations (24 countries; 60% from overseas), lively rump sessions and active participation by key figures including Professor Akasaki, the Honorary Chairman of the Conference ). Sponsored by the Japan Society of Applied Physics with co-sponsorship by the 162nd Committee on Wide Bandgap Semiconductor Photonic and Electronic Devices of the Japan Society for the Promotion of Science, technical sessions focused on topics ranging from growth and material characterisation to fabrication and commercialisation of devices such as high power FETs and laser diodes. This is a review of talks related to high power devices, AlGaN/GaN FETs, that have recently been the focus of intense scrutiny and may replace GaAs technology in the future.

A New Approach to Growth of Bulk Zno Crystals for Wide Bandgap Applications

ABSTRACTA novel technique was used to melt zinc oxide powder. This techniques involves the pressurized RF induction heating of ZnO, contained in a water-cooled crucible. The ability to obtain a pool of molten ZnO enables the pulling of large diameter ZnO crystals using conventional melt growth processes. Centimeter-sized crystals were obtained in the preliminary experiments by cooling the ZnO melt. These crystals were analyzed for crystalline perfection and stoichiometry using x-ray diffiraction and photoluminescence. The semiconductor properties of these crystals were also measured. This technology can potentially provide large, low cost ZnO single crystal wafers for use in the fabrication of GaN blue diodes and blue lasers, high temperature / high power FETs, as well as homoepitaxy of ZnO wide band-gap devices. Single crystal zinc oxide also has potential application in the piezoelectric device market.

Advances in millimeter-wave subsystems in Japan

The authors describe the development trends and results of millimeter-wave systems in Japan in such fields as communication, radar, and measurement systems. The applications included are the W-40G waveguide transmission communication system, an automobile traffic control system using the 60-GHz band, a collision avoidance radar system for an automobile, a plasma electron density measuring system, and satellite communication. The authors describe the development of devices such as high-power FET amplifiers, traveling wave tube amplifiers (TWTAs), IMPATT amplifiers, low-noise amplifiers, and monolithic microwave integrated circuit (MMIC) devices used in constructing the millimeter-wave systems. >

Two-dimensional electron transport and hot electron effects in InP/n-AlInAs heterostructures

Abstract We report two-dimensional electron gas (2DEG) transport in InP/n-AlInAs Heterostructures. This is the first demonstration of forming 2DEG in an InP with semiconductor heterojunctions. Temperature and electron density dependences of the 2DEG mobility are presented. This 2DEG system can be utilized for high speed and high power FETs. Hot electron gas transport in an InP is simulated with including electron-electron scattering and screening by high density electrons.

A linear voltage ramp generator for a three stage bunching system

Abstract A circuit capable of modulating the energy of a beam oor use with a three-stage bunching system has been designed and tested. This circuit charges up the anode of a duoplasmatron ion source through a resistor and discharges it through high power FETs at repetition rates of 4 MHz or 2 MHz. This new design represents an improvement over previous circuits in simplicity, reliability, and performance.

Foreword, Jun. 1976

Field-Effect Transistor Technology is a very dynamic field in microwaves today. Improvements in both low-noise and high-power FET's are being made continuously in many countries around the world. It is the purpose of this Special Issue to introduce this topic with a comprehensive review paper and to highlight advances in the development of microwave FET's and their applications. Authors from Japan, Europe, and North America report recent achievements of ongoing work in this issue. Their contributions reflect the following trends in the direction of developments.

Si UHF MOS high-power FET

An n-channel depletion-type Si UHF MOS power FET has been developed which exhibits 16.4-W output power, 6.1-dB power gain, and 35-percent drain efficiency at 700 MHz. The island-like n+source, interdigitated 5-µm-long and 20-mm-wide gate, and n+drain were fabricated in p on p+epitaxial wafer.