Low resistance ohmic contacts to Al-rich, AlGaN lateral transistors by MOCVD growth of heavily doped AlGaN alloys
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Allerman, Andrew Alan↗
Engineering topics
Joishi, Chandan
Publications and source records attributed to Joishi, Chandan.
Al-rich AlGaN alloys for RF and power transistors
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Allerman, Andrew A.↗
Tunnel junction-enabled monolithically integrated GaN micro-light emitting transistor
GaN/InGaN microLEDs are a very promising technology for next-generation displays. Switching control transistors and their integration are key components in achieving high-performance, efficient displays. Monolithic integration of microLEDs with GaN switching devices provides an opportunity to control microLED output power with capacitive (voltage)-controlled rather than current-controlled schemes. This approach can greatly reduce system complexity for the driver circuit arrays while maintaining device opto-electronic performance. In this work, we demonstrate a 3-terminal GaN micro-light emitting transistor that combines a GaN/InGaN blue tunneling-based microLED with a GaN n-channel FET. Further, the integrated device exhibits excellent gate control, drain current control, and optical emission control. This work provides a promising pathway for future monolithic integration of GaN FETs with microLED to enable fast switching, high-efficiency microLED display and communication systems.
42 ENGINEERING↗
Investigation of Interlayer Dielectric in BaTiO 3 /III–Nitride Transistors
In this paper, the impact of varying the thickness of the Al 2 O 3 interlayer dielectric on the electrical characteristics of BaTiO 3 /III-nitride transistors is investigated. In the findings, it is revealed that a minimum thickness of 8 nm for the Al 2 O 3 layer is crucial to maintain high device performance and protect against sputtering-induced damage during BaTiO 3 deposition. The fabricated BaTiO 3 /Al 2 O 3 /AlGaN/GaN high electron mobility transistors exhibit exceptional electrical properties, including a maximum current density of 700 mA mm –1 , an on-resistance of 5 Ω mm, an I ON /I OFF ratio of 10 7 , a subthreshold slope of 119 mV dec –1 , and significantly reduced gate leakage current. The devices with the optimal 8 nm Al 2 O 3 thickness demonstrates excellent agreement between theoretical and experimental values for effective mobility, achieving a value of 1188 cm 2 V –1 ·s at a 2D electron gas density of 10 13 cm –2 . Furthermore, in the study, it is confirmed that increasing the Al 2 O 3 thickness also improves the quality of interface charge density, as evidenced by the results obtained from capacitance–voltage measurements. In these findings, the critical role of controlling the Al 2 O 3 thickness in optimizing the electrical characteristics and overall performance of BaTiO 3 /III-nitride transistors are highlighted.
42 ENGINEERING↗
Addressing Challenges in AlGaN-Channel High Electron Mobility Transistors
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Klein, Brianna Alexandra↗
Al‐Rich AlGaN Transistors with Regrown p‐AlGaN Gate Layers and Ohmic Contacts
Abstract Epitaxial regrowth processes are presented for achieving Al‐rich aluminum gallium nitride (AlGaN) high electron mobility transistor (HEMTs) with p‐type gates with large, positive threshold voltage for enhancement mode operation and low resistance Ohmic contacts. Utilizing a deep gate recess etch into the channel and an epitaxial regrown p‐AlGaN gate structure, an Al 0.85 Ga 0.15 N barrier/Al 0.50 Ga 0.50 N channel HEMT with a large positive threshold voltage (V TH = +3.5 V) and negligible gate leakage is demonstrated. Epitaxial regrowth of AlGaN avoids the use of gate insulators which can suffer from charge trapping effects observed in typical dielectric layers deposited on AlGaN. Low resistance Ohmic contacts (minimum specific contact resistance = 4 × 10 −6 Ω cm 2 , average = 1.8 × 10 −4 Ω cm 2 ) are demonstrated in an Al 0.85 Ga 0.15 N barrier/Al 0.68 Ga 0.32 N channel HEMT by employing epitaxial regrowth of a heavily doped, n‐type, reverse compositionally graded epitaxial structure. The combination of low‐leakage, large positive threshold p‐gates and low resistance Ohmic contacts by the described regrowth processes provide a pathway to realizing high‐current, enhancement‐mode, Al‐rich AlGaN‐based ultra‐wide bandgap transistors.
36 MATERIALS SCIENCE↗
Plasma-assisted deposition and characterization of Al 2 O 3 dielectric layers on (001) β -Ga 2 O 3
In this work, we have investigated plasma-assisted deposition of Al 2 O 3 on HVPE (001) β-Ga 2 O 3 and evaluated the dielectric quality from electrical measurements on fabricated metal-oxide-semiconductor (MOS) capacitors. The interface structure and crystallinity of the films were investigated as a function of the growth temperature. The dielectric/semiconductor interfaces were found to have reverse breakdown electric fields up to 5.3 MV/cm in the β-Ga 2 O 3 , with relatively low hysteresis in capacitance–voltage and low leakage current. We determined a negative fixed interface charge density at the interface from analysis of thickness-dependent capacitance voltage data. In conclusion, this study shows the advantage of using plasma-assisted deposition to achieve high breakdown strength Al 2 O 3 /β-Ga 2 O 3 MOS structures for device application purposes.
42 ENGINEERING↗
β -Ga 2 O 3 trench Schottky diodes by low-damage Ga-atomic beam etching
β-Ga 2 O 3 trench Schottky barrier diodes fabricated through a Gallium atomic beam etching technique with excellent field strength and power device figure of merit are demonstrated. Trench formation was accomplished by a low-damage Ga flux etch that enables near-ideal forward operating characteristics that are independent of fin orientation. The reverse breakdown field strength of greater than 5.10 MV/cm is demonstrated at a breakdown voltage of 1.45 kV. This result demonstrates the potential for Ga atomic beam etching and high-quality dielectric layers for improved performance in β-Ga 2 O 3 vertical power devices.
42 ENGINEERING↗
Wireless System Development for GaN-Based Transmitters for Advanced Nuclear Reactor Environments
The market for consumer electronics is dominated by Si-based electronics. Many Si-based complementary metal–oxide–semiconductor (CMOS) devices are reaching their limitations in terms of switching frequencies, voltages, currents, and temperatures. Furthermore, these devices are widely known to be susceptible to ionizing radiation and neutrons. Advanced nuclear reactors, especially microreactors and small modular reactors, require wireless electronics that can survive larger neutron and gamma doses than Si CMOS. Because of their size, electronics will need to be placed closer to the reactor cores, and cabling capabilities may be limited. However, GaN high-electron-mobility transistors (HEMTs) have been shown to switch faster with higher gains, and they can achieve current and voltage limits beyond traditional Si CMOS. However, they have less market maturity and have undergone less testing. These GaN HEMTs have been shown to survive ionizing radiation with little effects, but the effects of neutron radiation remain widely unknown. In this report, a wireless electronic system capable of supporting multiple radiation-hardened (rad-hard) sensors is presented. The proposed transmission scheme was designed to be simple to increase the likelihood of success in the immature GaN HEMT process and in high-radiation environments. The transmission system was tested using software-defined radios to emulate the transmission scheme before the transmitter circuitry in the GaN process was developed.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
β -Ga 2 O 3 Schottky barrier diodes with 4.1 MV/cm field strength by deep plasma etching field-termination Available
In this work, we demonstrate a deep mesa etch design for efficient edge field termination in β-Ga 2 O 3 Schottky barrier diodes (SBDs). The proposed design enabled parallel plate fields higher than 4.1 MV/cm with negligible change to the device ON characteristics. The effect of BCl 3 /Cl 2 -based dry etch on (100) and (010) etched vertical sidewalls is also analyzed. A remarkable anisotropy in depletion was observed for etch along (100) and (010) sidewalls. In conclusion, this work provides insight into the impact of etching on n-type Ga 2 O 3 and shows a promising method to realize efficient field termination for high breakdown field strength SBDs.
42 ENGINEERING↗
Radiation-Hardened GaN HEMT and Cell Design, Modeling, and Fabrication for Nuclear Instrumentation Applications
Recent advances in nuclear power generation technologies show great promise for efficient, safe generation of carbon-free power in the near future. Consequently, many new generation reactor designs are being pursued by government and industry groups, including both fission- and fusion-based technologies. Radiation- and temperature-tolerant sensor technology continues to advance, yet development of the electronics/instrumentation technologies suitable for these environments have fallen behind. Industry has adequately addressed harsh environment electronics needs for low earth orbit satellites, but the much more extreme conditions associated with electronics placed near or in a reactor core remain unaddressed. This project investigates the use of gallium nitride (GaN) circuit technology to address the unique needs for sensor interface electronics and communications in reactor environments. This report provides a summary of the first year’s project activities related to developing and optimizing devices and circuits for this GaN high electronic mobility transistor (HEMT) process. Activities reported include multiple analog and digital circuit designs simulated using custom Verilog-A models generated from measured GaN devices fabricated in the target process. Digital circuit designs included fundamental logic circuits such as an inverter, NAND, NOR, AND and OR gates, as well as a 5-stage ring oscillator. Each design was simulated using an open-source SPICE simulator, and an integrated circuit layout was produced of each design for use in future fabrication. Analog circuit designs focused on the fundamental building blocks to be used to construct sensor interface and communications circuits. These included current mirrors, matched differential pairs, and a Gilbert cell mixer design, each with an associated integrated circuit layout. Layout tools used for these designs included two open-source packages—KLayout and Magic—which were customized for specific use with the OSU GaN process layers. Design rules and preliminary device extraction capabilities were built for the Magic tool to enable device extraction and subsequent netlist generation for SPICE simulation. Finally, future research directions for year two are summarized. When the year-two directions are implemented, the project will be in position to advance the state of the art in electronics for near- or in-reactor sensor interfacing and communications.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
Radiation-Hardened GaN-Based Wireless Communications Architectures for Terrestrial Nuclear Reactor Sensing and Instrumentation
Wireless technologies have become increasingly common in applications, ranging from close proximity inductive communication links in medical devices to short-range Bluetooth and WiFi communications and longer-range cellular communications. Nonetheless, these technologies are unsuitable for use in or around nuclear reactors due to the extreme radiation and temperatures inherent in these environments and their associated significant degradative effects on electronics hardware. However, recent work in wide bandgap– based electronics has shown promise for gallium nitride (GaN) as an emerging technology for the realization of practical wireless communications systems for use in harsh environments. This report presents initial progress on the development of wireless communications architectures designed specifically for nuclear reactor application, based on inherently radiation-hardened (rad-hard) GaN technology. Prior work on rad-hard analog communications topologies is reviewed, and several digital modulation and encoding schemes that utilize GaN-based electronics devices are newly proposed for application in reactor environments. Continuous-time and discrete-time system simulations were performed, and results are presented for the preliminary transmitter and receiver designs, respectively. In addition, an overview of a software-defined radio testbed, designed for communications protocol development, is provided. Future work will focus on implementing candidate radiation-resistant wireless architectures using a research AlGaN/GaN high electron mobility transistor (HEMT) integrated circuit process, which is available at the Ohio State University, and irradiation studies will be carried out to assess the true potential of this technology for reactor application.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗
GaN HEMT Fabrication for Radiation-Hardened Sensing and Communications Electronics
Gallium nitride (GaN), a wide bandgap semiconductor, has vast potential to address two environment conditions associated with the application of electronics to nuclear power: elevated temperatures, and high levels of radiation. A process was developed at The Ohio State University (OSU) to enable fabrication of complex digital and analog electronics circuits for application to nuclear power environments such as locations near or in the reactor core or in spent nuclear fuel casks. Radio frequency (RF)-grade GaN high electron mobility transistor (HEMT) devices were fabricated as part of this process. These were fabricated as depletion mode and enhancement mode devices. They have been electrically characterized and have demonstrated the expected performance. Behavioral models (Verilog-A) were developed from these device measurements to enable electrical simulation of GaN HEMT devices and circuits using common electronics simulation tools based on Simulation Program with Integrated Circuit Emphasis (SPICE). A similar set of GaN HEMT devices is being developed to provide lower speed devices for logic and analog functions. These accomplishments position this technology for effective application to sensor interfacing, signal processing, and data communications in nuclear power plants, including operation in or near the reactor core.
22 GENERAL STUDIES OF NUCLEAR REACTORS↗