This paper reviews the recent activities for normally-off GaN-based gate injection transistors (GITs) on Si substrates and their application to inverters. Epitaxial growth of the AlGaN/GaN heterostructures with good crystallinity over 200-mm Si substrates with eliminated bowing enables low-cost fabrication of GaN devices with high breakdown voltages. A novel normally-off GaN transistor called as GIT is proposed in which hole injection from the p-type AlGaN gate increases the drain current with low on-state resistance by conductivity modulation. The low on-state resistance in GaN-based devices greatly helps to increase the efficiency of power switching systems. A GaN-based three-phase inverter successfully drives a motor with high efficiency of 99.3% at a high output power of 1500 W. The presented GaN-based devices are expected to greatly help saving energy in the future as an indispensable power switching system.

GaN on Si Technologies for Power Switching Devices

Two layers of protection films are formed such that a sheet resistance at a portion directly below the protection film is higher than that at a portion directly below the protection film. The protection films are formed, for example, of SiN film, as insulating films. The protection film is formed to be higher, for instance, in hydrogen concentration than the protection film so that the protection film is higher in refractive index the protection film. The protection film is formed to cover a gate electrode and extend to the vicinity of the gate electrode on an electron supplying layer. The protection film is formed on the entire surface to cover the protection film. According to this configuration, the gate leakage is significantly reduced by a relatively simple configuration to realize a highly-reliable compound semiconductor device achieving high voltage operation, high withstand voltage, and high output.

Compound semiconductor device and method of manufacturing the same

Power semiconductor devices based on silicon (Si) are quickly approaching their limits, set by fundamental material properties. In order to address these limitations, new materials for use in devices must be investigated. Wide bandgap materials, such as silicon carbide (SiC) and gallium nitride (GaN) have suitable properties for power electronic applications; however, fabrication of practical devices from these materials may be challenging. SiC technology has matured to point of commercialized devices, whereas GaN requires further research to realize full material potential. This review covers fundamental material properties of GaN as they relate to Si and SiC. This is followed by a discussion of the contemporary issues involved with bulk GaN substrates and their fabrication and a brief overview of how devices are fabricated, both on native GaN substrate material and non-native substrate material. An overview of current device structures, which are being analyzed for use in power switching applications, is then provided; both vertical and lateral device structures are considered. Finally, a brief discussion of prototypes currently employing GaN devices is given.

GaN Technology for Power Electronic Applications: A Review

In one aspect of the present disclosure, a semiconductor device includes a channel layer, an AlxIn1-xN layer on the channel layer with a thickness of t1, and a reverse polarization layer on the AlxIn1-xN layer with a thickness of t2. The thickness is 0.5*t1<=t2<=3*t1. In another aspect of the present disclosure, a method of manufacturing a semiconductor device is provided. The method including: forming a channel layer on a substrate; forming an AlxIn1-xN layer on the channel layer with a thickness of t1; and forming a reverse polarization layer on the AlxIn1-xN layer with a thickness of t2. The thickness is 0.5*t1<=t2<=3*t1.

Semiconductor device and method of fabricating the same

GalliumNitridebasedhighelectronmobilitytransistors(HEMTs)areattractiveforuseinhighpowerandhighfrequencyapplications, with higher breakdown voltages and two dimensional electron gas (2DEG) density compared to their GaAs counterparts. Specific applications for nitride HEMTs include air, land and satellite based communications and phased array radar. Highly efficient GaNbased blue light emitting diodes (LEDs) employ AlGaN and InGaN alloys with different compositions integrated into heterojunctions and quantum wells. The realization of these blue LEDs has led to white light sources, in which a blue LED is used to excite a phosphor material; light is then emitted in the yellow spectral range, which, combined with the blue light, appears as white. Alternatively, multiple LEDs of red, green and blue can be used together. Both of these technologies are used in high-efficiency white electroluminescent light sources. These light sources are efficient and long-lived and are therefore replacing incandescent and fluorescent lamps for general lighting purposes. Since lighting represents 20‐30% of electrical energy consumption, and because GaN white light LEDs require ten times less energy than ordinary light bulbs, the use of efficient blue LEDs leads to significant energy savings. GaN-based devices are more radiation hard than their Si and GaAs counterparts due to the high bond strength in III-nitride materials. The response of GaN to radiation damage is a function of radiation type, dose and energy, as well as the carrier density, impurity content and dislocation density in the GaN. The latter can act as sinks for created defects and parameters such as the carrier removal rate due to trapping of carriers into radiation-induced defects depends on the crystal growth method used to grow the GaN layers. The growth method has a clear effect on radiation response beyond the carrier type and radiation source. We review data on the radiation resistance of AlGaN/GaN and InAlN/GaN HEMTs and GaN‐based LEDs to different types of ionizing radiation, and discuss ion stopping mechanisms. The primary energy levels introduced by different forms of radiation, carrier removal rates and role of existing defects in GaN are discussed. The carrier removal rates are a function of initial carrier concentration and dose but not of dose rate or hydrogen concentration in the nitride material grown by Metal Organic Chemical Vapor Deposition. Proton and electron irradiation damage in HEMTs creates positive threshold voltage shifts due to a decrease in the two dimensional electron gas concentration resulting from electron trapping at defect sites, as well as a decrease in carrier mobility and degradation of drain current and transconductance. State-of-art simulators now provide accurate predictions for the observed changes in radiation-damaged HEMT performance. Neutron irradiation creates more extended damage regions and at high doses leads to Fermi level pinning while 60 Co γ-ray irradiation leads to much smaller changes in HEMT drain current relative to the other forms of radiation. In InGaN/GaN blue LEDs irradiated with protons at fluences near 10 14 cm −2 or electrons at fluences near 10 16 cm −2 , both current-voltage and light output-current characteristics are degraded with increasing proton dose. The optical performance of the LEDs is more sensitive to the proton or electron irradiation than that of the corresponding electrical performances. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

https://iopscience.iop.org/article/10.1149/2.0251602jss/pdf

Review—Ionizing Radiation Damage Effects on GaN Devices

This letter presents details of high-performance enhancement-mode GaN MIS high-electron-mobility transistor (MIS-HEMT) devices. Devices with an n-GaN/i-AlN/n-GaN triple cap layer, a recessed-gate structure, and high- k gate dielectrics show high drain current and complete enhancement-mode operation. The maximum drain current and threshold voltage (V th) are 800 mA/mm and +3 V, respectively. These results indicate that a recessed AlGaN/GaN MIS-HEMT with the triple cap could be a promising new technology for future device applications.

Enhancement-Mode GaN MIS-HEMTs With n-GaN/i-AlN/n-GaN Triple Cap Layer and High- $k$ Gate Dielectrics

This letter reports on an InAlGaN/GaN high-electron-mobility transistor (HEMT) employing a SiC/diamond-bonded heat spreader with a record high output power density of 22.3 W/mm. A quaternary In-added InAlGaN barrier enabled both the large current of over 1 A/mm and the high breakdown voltage of 257 V. The drain bias was increased as high as 100 V for the S-band load-pull measurement, leading to high power operation. Furthermore, the thermal resistance was reduced by 60%, from 18.8 to 7.2°C/W, by employing the SiC/diamond heat spreader. This large heat dissipation effect was clearly observed in the output power density for the load-pull measurement. Our results demonstrate that the GaN HEMT with an In-added barrier layer is promising not only for millimeter-wave applications but also for high output power microwave amplifiers.

An Over 20-W/mm S-Band InAlGaN/GaN HEMT With SiC/Diamond-Bonded Heat Spreader

In this paper, we report a C-band power amplifier with over 340-W output power using 0.8-µm GaN-HEMTs and an X-band power amplifier with over 100-W output power using 0.25-µm GaN-HEMTs. We used two-chip configurations and the three-stage impedance transformers to extend the bandwidth for both circuits. The input and output lines adjacent to each chip are divided by four to suppress the non-uniform heat distribution in a chip at high frequencies. As a result, we obtained 343-W output power and 53-% power added efficiency (PAE) at 4.8 GHz. This is the highest output power ever reported C-band power amplifiers. We also obtained 101-W output power and 53-% PAE at 9.8 GHz. This is also the highest PAE ever reported X-band power amplifiers with over 50-W output power.

C-band 340-W and X-band 100-W GaN power amplifiers with over 50-% PAE

https://iopscience.iop.org/article/10.7567/1347-4065/ab5b68/pdf

Surface activated bonding of SiC/diamond for thermal management of high-output power GaN HEMTs

This paper investigates the effects of MOVPE growth parameters on the gate leakage characteristics of InAlN HEMT structures and compares leakage current paths in AlGaN and InAlN HEMT structures on a nanometer scale. The gate leakage characteristics of AlGaN and InAlN HEMT were compared, and the large leakage current in InAlN HEMT was found to result from the high-density 2DEG-induced strong electric field accumulation in the barrier layer. Both the increasing growth rate and decreasing growth temperature in the InAIN layer of InAlN HEMT caused the deterioration of gate leakage characteristics and surface morphologies. Conductive AFM measurements were performed for AlGaN and InAlN HEMT structures, and a one-to-one clear correlation between surface pits and leakage paths was found for AlGaN HEMT. On the contrary, for the InAlN HEMT grown at a low temperature, high-density localized leakage paths were observed. We believe the observed leakage paths originate from nanometer-scale material fluctuations, which is most likely an indium composition fluctuation. Our results indicate that it is necessary to grow the InAlN barrier layer at 740 °C or higher and that the growth rate must be 1.25 nm min−1 or less to realize low-gate leakage in InAlN HEMT. A further reduction of the gate leakage current requires the reduction of the dislocation density and use of gate insulators.

Atsushi Yamada

Papers

Enhancement-Mode GaN MIS-HEMTs With n-GaN/i-AlN/n-GaN Triple Cap Layer and High- $k$ Gate Dielectrics

An Over 20-W/mm S-Band InAlGaN/GaN HEMT With SiC/Diamond-Bonded Heat Spreader

C-band 340-W and X-band 100-W GaN power amplifiers with over 50-% PAE

Surface activated bonding of SiC/diamond for thermal management of high-output power GaN HEMTs

Direct observation of nanometer‐scale gate leakage paths in AlGaN/GaN and InAlN/AlN/GaN HEMT structures