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

New developments in theoretical studies of defects and impurities in III-Nitrides as pertinent to compensation and recombination in these materials are discussed. New results on experimental studies on defect states of Si, O, Mg, C, Fe in GaN, InGaN, and AlGaN are surveyed. Deep electron and hole traps data reported for GaN and AlGaN are critically assessed. The role of deep defects in trapping in AlGaN/GaN, InAlN/GaN structures and transistors and in degradation of transistor parameters during electrical stress tests and after irradiation is discussed. The recent data on deep traps influence on luminescent efficiency and degradation of characteristics of III-Nitride light emitting devices and laser diodes are reviewed.

Deep traps in GaN-based structures as affecting the performance of GaN devices

A review of the effects of proton, neutron, γ-ray, and electron irradiation on GaN materials and devices is presented. Neutron irradiation tends to create disordered regions in the GaN, while the damage from the other forms of radiation is more typically point defects. In all cases, the damaged region contains carrier traps that reduce the mobility and conductivity of the GaN and at high enough doses, a significant degradation of device performance. GaN is several orders of magnitude more resistant to radiation damage than GaAs of similar doping concentrations. In terms of heterostructures, preliminary data suggests that the radiation hardness decreases in the order AlN/GaN > AlGaN/GaN > InAlN/GaN, consistent with the average bond strengths in the Al-based materials.

Review of radiation damage in GaN-based materials and devices

This article reviews the effects of radiation damage on GaN materials and devices such as light-emitting diodes and high electron mobility transistors. Protons, electrons and gamma rays typically produce point defects in GaN, in contrast to neutron damage which is dominated by more extended disordered regions. Regardless of the type of radiation, the electrical conductivity of the GaN is reduced through the introduction of trap states with thermal ionization energies deep in the forbidden bandgap. An important practical parameter is the carrier removal rate for each type of radiation since this determines the dose at which device degradation will occur. Many studies have shown that GaN is several orders of magnitude more resistant to radiation damage than GaAs, i.e. it can withstand radiation doses of at least two orders of magnitude higher than those degrading GaAs with a similar doping level. Many issues still have to be addressed. Among them are the strong asymmetry in carrier removal rates in n- and p-type GaN and interaction of radiation defects with Mg acceptors and the poor understanding of interaction of radiation defects in doped nitrides with the dislocations always present.

Radiation effects in GaN materials and devices

With the largest band gap energy of all commercial semiconductors, GaN has found wide application in the making of optoelectronic devices. It has also been used for photodetection such as solar blind imaging as well as ultraviolet and even X-ray detection. Unsurprisingly, the appreciable advantages of GaN over Si, amorphous silicon (a-Si:H), SiC, amorphous SiC (a-SiC), and GaAs, particularly for its radiation hardness, have drawn prompt attention from the physics, astronomy, and nuclear science and engineering communities alike, where semiconductors have traditionally been used for nuclear particle detection. Several investigations have established the usefulness of GaN for alpha detection, suggesting that when properly doped or coated with neutron sensitive materials, GaN could be turned into a neutron detection device. Work in this area is still early in its development, but GaN-based devices have already been shown to detect alpha particles, ultraviolet light, X-rays, electrons, and neutrons. Furthermo...

https://nars.osu.edu/sites/nars.osu.edu/files/uploads/cao-gan_review_for_radiatino_detection.pdf

Review of using gallium nitride for ionizing radiation detection

Ni/GaN Schottky diode radiation detectors were fabricated on 3-μm-thick unintentionally doped n-GaN films grown by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) and on 12-μm-thick undoped n-GaN layers prepared by epitaxial lateral overgrowth (ELOG). The reverse current of all detector structures was <10−9 A for bias voltages necessary for detector operation, with the level of background donor doping of <1015 cm−3. With this doping level the space charge region of the Schottky diode could be extended to the entire thickness of the films. The charge collection efficiency of the detectors was close to 100% for MOCVD and ELOG detectors for α-particles with range comparable to the thickness of the layer. Electrical properties and deep trap spectra were also studied. The collection efficiency decreased when the concentra-tion of deep electron traps, particularly Ec-0.6 eV traps, increased in MBE grown films.

Alpha particle detection with GaN Schottky diodes

The effects of neutron transmutation doping were studied for undoped (residual donor concentrations <1015 cm−3) GaN films grown by metalorganic chemical vapor deposition After irradiation with reactor neutrons (equal fluences of 15×1017 n/cm2 of thermal and fast neutrons) the sample became semi-insulating, with the Fermi level pinned near Ec−08 eV Isochronal annealing from 100 to 1000 °C showed three stages—slight recovery of conductivity at 200–300 °C, reverse annealing at 300–500 °C, and a broad recovery stage from 600 to 1000 °C After annealing at 1000 °C, the donor concentration in the sample was close to the expected concentration of Ge donors transformed from Ga atoms upon interaction with thermal neutrons (2×1016 cm−3) Admittance spectroscopy showed that the donors had ionization energies ∼Ea=02 eV, much deeper than substitutional Ge donors For intermediate annealing temperatures of 800 °C the donors were deeper (Ea=047 eV), but the proximity of concentrations of all these different center

Neutron transmutation doping effects in GaN

We studied 10 MeV electron irradiation effects in a group of n-GaN films grown by standard metalorganic chemical vapor deposition (MOCVD) and by epitaxial lateral overgrowth (ELOG) techniques. The samples were either undoped or Si-doped, so that the shallow donor concentrations ranged from 1014 cm−3 to 3 × 1018 cm−3. It was found that electron irradiation led to the compensation of n-type conductivity and that the carrier removal rate substantially increased with an increase in the starting donor concentration. For the MOCVD samples, it was observed that the main compensating defect introduced by electrons was a 0.15 eV electron trap detected by admittance spectroscopy. Once the Fermi level crossed the level of these traps two other centers with activation energies of 0.2 and 1 eV were found to contribute to the compensation, so that after high doses, the Fermi level in moderately doped samples was pinned near Ec −1 eV. In ELOG samples the 0.15 eV electron traps were not detected. Instead only the 0.2 and...

10 MeV electrons irradiation effects in variously doped n-GaN

In neutron transmutation doped n-GaN, the electrical properties are found to be dominated not by shallow Ge donors produced by interaction of thermal neutrons with Ga, but by electron traps at 0.45 or 0.2 eV. The traps switch from the former to the latter when the anneal temperature increased from 800 to 1000 °C. The concentrations of both traps rose linearly with neutron fluence and were close to the concentration of Ge donors, suggesting they are Ge complexed with different radiation defects. The authors note the similarity of the properties of these traps to the properties of the dominant electron traps in as-irradiated n-GaN. They also observed prominent hole traps with a level near Ev+1.2 eV. These traps were not detected in virgin or as-irradiated samples. The concentration of the 1.2 eV hole traps increased linearly with neutron fluence, and these traps were assigned to Ga vacancy complexes with oxygen.

A. V. Korulin

Papers

Alpha particle detection with GaN Schottky diodes

Neutron transmutation doping effects in GaN

10 MeV electrons irradiation effects in variously doped n-GaN

Deep electron and hole traps in neutron transmutation doped n-GaN

Carrier Removal Rates and Deep Traps in Neutron Irradiated n-GaN Films