The 2018 GaN Power Electronics Roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

The 2018 GaN power electronics roadmap

GaN is a compound semiconductor that has a tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

The 2018 GaN power electronics roadmap

Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here

GaN Power Devices: Discerning Application-Specific Challenges and Limitations in HEMTs

GaN power devices are typically used in the 600 V market, for high efficiency, high power-density systems. For these devices, the lateral optimization of gate-to-drain, gate, and gate-to-source lengths, as well as gate field-plate length are critical for optimizing breakdown voltage and performance. This work presents a systematic study of lateral scaling optimization for high voltage devices to minimize figure of merit and maximize breakdown voltage. In addition, this optimization is extended for low voltage devices ( \u3c 100 V), presenting results to optimize both lateral features and vertical features. For low voltage design, simulation work suggests that breakdown is more reliant on punch-through as the primary breakdown mechanism rather than on vertical leakage current as is the case with high-voltage devices. A fabrication process flow has been developed for fabricating Schottky-gate, and MIS-HEMT structures at UCF in the CREOL cleanroom. The fabricated devices were designed to validate the simulation work for low voltage GaN devices. The UCF fabrication process is done with a four layer mask, and consists of mesa isolation, ohmic recess etch, an optional gate insulator layer, ohmic metallization, and gate metallization. Following this work, the fabrication process was transferred to the National Nano Device Laboratories (NDL) in Hsinchu, Taiwan, to take advantage of the more advanced facilities there. Following fabrication, a study has been performed on defect induced performance degradation, leading to the observation of a new phenomenon: trap induced negative differential conductance (NDC). Typically NDC is caused by self-heating, however by implementing a substrate bias test in conjunction with pulsed I-V testing, the NDC seen in our fabricated devices has been confirmed to be from buffer traps that are a result of poor channel carrier confinement during the dc operating condition

Wide Bandgap Based Devices

Emerging wide bandgap (WBG) semiconductors hold the potential to advance the global industry in the same way that, more than 50 years ago, the invention of the silicon (Si) chip enabled the modern computer era. SiC- and GaN-based devices are starting to become more commercially available. Smaller, faster, and more efficient than their counterpart Si-based components, these WBG devices also offer greater expected reliability in tougher operating conditions. Furthermore, in this frame, a new class of microelectronic-grade semiconducting materials that have an even larger bandgap than the previously established wide bandgap semiconductors, such as GaN and SiC, have been created, and are thus referred to as “ultra-wide bandgap” materials. These materials, which include AlGaN, AlN, diamond, Ga2O3, and BN, offer theoretically superior properties, including a higher critical breakdown field, higher temperature operation, and potentially higher radiation tolerance. These attributes, in turn, make it possible to use revolutionary new devices for extreme environments, such as high-efficiency power transistors, because of the improved Baliga figure of merit, ultra-high voltage pulsed power switches, high-efficiency UV-LEDs, and electronics. This Special Issue aims to collect high quality research papers, short communications, and review articles that focus on wide bandgap device design, fabrication, and advanced characterization. The Special Issue will also publish selected papers from the 43rd Workshop on Compound Semiconductor Devices and Integrated Circuits, held in France (WOCSDICE 2019), which brings together scientists and engineers working in the area of III–V, and other compound semiconductor devices and integrated circuits

Wide Bandgap Based Devices: Design, Fabrication and Applications, Volume II

Wide bandgap (WBG) semiconductors are becoming a key enabling technology for several strategic fields, including power electronics, illumination, and sensors. This reprint collects the 23 papers covering the full spectrum of the above applications and providing contributions from the on-going research at different levels, from materials to devices and from circuits to systems

Study of Ultra Wide Band Gap AlxGa1-xN Field Effect Transistors For Power Electronic Applications

High Aluminum content AlxGa1-xN (x \u3e 30%) has attracted intense research interest nowadays as “Ultra Wide Band Gap (UWBG)” material due to large band gap (\u3e 3.4 eV). The critical electric field (EC) of UWBG semiconductor AlGaN is significantly higher than GaN. Moreover, electron saturation velocity is also comparable to GaN. These attractive material properties are the needs for getting large breakdown voltage and high thermal stability which are the requirements for next generation power semiconductor devices. Theoretical possibilities show UWBG AlGaN based devices are an emerging class and can outperform conventional GaN based devices even at elevated temperatures. This dissertation focuses on design, fabrication, and characterization of UWBG semiconductor AlGaN based Field Effect Transistors. Along with detailed electrical and thermal characterization, a brief study on optical characterization is also performed to understand the potential of UWBG semiconductor AlGaN based devices as UV detector which has many important commercial and military applications. The work started with brief explanation of material growth and characterization. This includes discussion on structural and surface morphological analysis of the active epilayers grown on AlN (3μm)/Sapphire templates conventionally used for Deep Ultra Violet Light Emitting Diodes (DUV LEDs). The off-axes (102) X-ray peak line width of this AlN buffers was measured to be 350 arc-sec which translates the overall defect density close to (1-3) × 108 cm-2. The device epilayers were grown on these templates pseudo morphically. Electrical characterizations of these epilayers are performed by eddy current method and mercury probe Capacitance-Voltage (C-V) method. The transmission spectra measurement is also performed to get the optical absorption edge. A series of experiments have been made to realize the Field Effect Transistors (FETs). As a first step of making UWBG based Field Effect Transistors an n-Al0.5Ga0.5N channel Metal Semiconductor Field Effect Transistor (MESFET) was fabricated by Selective Area Growth (SAG) technique for the first time which shows 60 mA/mm current with good gate control. For studying the effect of gate insulator another set of similar type of devices were fabricated with SiO2 as gate insulator which reduces gate current by a factor of 1000. These devices show very high optical responsivity as 1.2×106 A/W which drops after 290 nm of wavelength and shows greater promise as solar blind UV detector. After that Aluminum mole fraction was increased to 65% in the MESFET channel layer. Nonlinearity in Ohmic contacts motivated to develop a new approach of Selective Area Graded n-AlGaN based Ohmic contact. Extensive thermal characterizations have been performed. It is found that up to 200 oC the change in drain saturation current is only \u3c 10%. These devices also showed 254 nm UV detection capabilities at 200 oC. For getting better switching performance i-Al0.65Ga0.35N channel based HEMT was designed and fabricated. In this case i-Al0.85Ga0.15N and n-Al0.85Ga0.15N barriers were employed separately. Large bandgap of the barrier layer results extremely low gate leakage current in the order of 10-9 A/mm. The peak current obtained was 250 mA/mm which is the highest till to date for UWBG semiconductor AlGaN channel based HEMT. The on current to off current ratio (ION/IOFF) was \u3e 107 which shows the good switching quality of this power semiconductor device. Even at elevated temperature of 250 oC, the ION/IOFF ~ 105. The change in drain saturation current is \u3c 10% at 250 oC which is similar for devices on expensive bulk AlN substrate. The breakdown voltage was close to 800V for gate to drain separation of 9 µm for these un-passivated devices with no filed plate and edge termination. All these results indicate that UWBG AlGaN channel based FETs have greater promise for next generation high power and high temperature power electronic applications in low cost platform. Also, the optical characterization reveals the possibility to open new device applications scope where photonic and electronic devices can be used on the same chip for high temperature operation