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

We present the results of a radiation damage experiment on AlxGa1-xN/GaN high electron mobility transistors. The basic mechanism underlying the observed high radiation tolerance appears to be a strong internal piezoelectric field near the two-dimensional electron gas that causes scattered carriers to be reinjected.

Displacement Damage Effects in AlGaN/GaN High Electron Mobility Transistors

The radiation tolerance of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on high quality, low threading dislocation density (TDD) ammonothermal GaN and hydride vapor phase epitaxy GaN substrates was studied and compared to the radiation response of devices on SiC substrates where the TDD is 104 times higher. Hall and transport measurements were performed as a function of 2 MeV proton fluence. The threading dislocation density had no effect on the radiation response. Comparing the results with published data reveals that almost all irradiated GaN-based HEMTs respond to radiation damage similarly regardless of differences in initial film quality, device structure, aluminum mole fraction, etc. AlGaAs/GaAs HEMTs are also shown to behave similarly but are around ten times more sensitive to radiation damage than GaN-based HEMTs. Known values of the displacement energy thresholds in GaN and GaAs are used to calculate that 36% fewer defects are created in GaN than in GaAs, which is too small to cause a 1000% difference in radiation sensitivity between GaN- and GaAs-based HEMTs. An alternative explanation is proposed in which the piezoelectric field at the AlGaN/GaN interface causes scattered carriers to be reinjected into the 2DEG channel, thereby mitigating some of the harmful radiation effects.

Editors' Choice—On the Radiation Tolerance of AlGaN/GaN HEMTs

Transient currents in AlGaN/GaN High Electron Mobility Transistors (HEMTs) induced by focused ion beams are measured. Enhanced charge collection occurs in the on- and pinch-off states of AlGaN/GaN HEMTs. The first-order mechanism of enhancement is associated with bipolar and back-channel effects. In addition, we suggest that the temporal positive charge buildup contributes to the enhanced charge collection. The effect of displacement damage on the enhanced charge collection is also discussed.

Enhanced Charge Collection by Single Ion Strike in AlGaN/GaN HEMTs

AlGaN/AlN/GaN/sapphire, AlGaN/GaN/sapphire, AlGaN/GaN/Si, and InAlN/GaN/sapphire heterojunctions (HJs) were irradiated with 10 MeV electrons to fluences of 2 × 1015 to 3.3 × 1016 cm−2. The main effects on the electrical properties were a decrease in two-dimensional electron gas (2DEG) mobility and the shift of capacitance–voltage (C-V) characteristics to more positive values. The 50% 2DEG mobility decrease occurred at a similar fluence of 3.3 × 1016 cm−2 for all AlGaN/GaN and AlGaN/AlN/GaN HJs, but at a much lower fluence of 1.3 × 1016 cm−2 for InAlN/GaN, which is in line with previous observations for neutron irradiated HJs. The shift of C-V characteristics is due to increased concentration of deep acceptor traps in the barrier/interface region. In AlGaN/GaN/Si transistors, the increase of concentration of deep barrier/interface traps with activation energy of 0.3, 0.55, and 0.8 eV was observed. This increase correlates with the observed degradation of gate lag characteristics of transistors after irradiation with 1.3 × 1016 cm−2 electrons.

Effect of electron irradiation on AlGaN/GaN and InAlN/GaN heterojunctions

The effects of low energy (0.45 MeV) electron radiation on the gate and drain currents of Al0.27Ga0.73N/GaN HFETs are investigated using IV and CV measurements. Following irradiation, the gate and drain currents increase at low temperatures and reach a saturation level. The gate leakage currents do not fully account for the drain current increase. Following a room temperature anneal, the gate and drain currents return to pre-irradiation levels. These results are explained by the buildup of positive charge in the AlGaN layer at low temperature and traps formed via a complexing precursor in the AlGaN layer near the interface. The positive charge increases the carrier concentration in the 2DEG and hence the drain current. The traps act as trap-assisted-tunneling centers that increase the gate leakage current.

T.A. Jarzen

Papers

An Analysis of the Effects of Low-Energy Electron Irradiation of AlGaN/GaN HFETs