Carrier Removal Rate Research Articles

Forward bias annealing of proton radiation damage in NiO/Ga2O3 rectifiers

17 MeV proton irradiation at fluences from 3–7 × 1013 cm−2 of vertical geometry NiO/β-Ga2O3 heterojunction rectifiers produced carrier removal rates in the range 120–150 cm−1 in the drift region. The forward current density decreased by up to 2 orders of magnitude for the highest fluence, while the reverse leakage current increased by a factor of ∼20. Low-temperature annealing methods are of interest for mitigating radiation damage in such devices where thermal annealing is not feasible at the temperatures needed to remove defects. While thermal annealing has previously been shown to produce a limited recovery of the damage under these conditions, athermal annealing by minority carrier injection from NiO into the Ga2O3 has not previously been attempted. Forward bias annealing produced an increase in forward current and a partial recovery of the proton-induced damage. Since the minority carrier diffusion length is 150–200 nm in proton irradiated Ga2O3, recombination-enhanced annealing of point defects cannot be the mechanism for this recovery, and we suggest that electron wind force annealing occurs.

Synergistic effect of electrical bias and proton irradiation on the electrical performance of β-Ga2O3 p–n diode

The synergistic impact of reverse bias stress and 3 MeV proton irradiation on the β-Ga2O3 p–n diode has been studied from the perspective of the defect in this work. The forward current density (JF) is significantly decreased with the increase in proton irradiation fluence. According to the deep-level transient spectroscopy results, the increase in the acceptor-like trap with an energy level of EC-0.75 eV within the β-Ga2O3 drift layer, which is most likely to be Ga vacancy-related defects, can be the key origin of the device degradation. The increase in these acceptor-like traps results in the carrier concentration reduction, which in turn leads to a decrease in JF. Furthermore, compared with the case of proton irradiation with no bias, the introduction of −100 V electrical stress induced a nearly double decrease in JF. Based on the capacitance–voltage (C–V) measurement, with the support of the electric field, the carrier removal rate increased from 335 to 600 cm−1. Similar to the above-mentioned phenomenon, the trap concentration also increased significantly. We propose a hypothesis elucidating the synergistic effect of electrical stress and proton irradiation through the behavior of recoil nuclei under the electric field.

Radiation effects of high-fluence reactor neutron on Ni/ β -Ga2O3 Schottky barrier diodes

This study investigates the broad-energy-spectrum reactor-neutron irradiation effects on the electrical characteristics of Ni/β-Ga2O3 Schottky barrier diodes (SBDs), where the irradiated neutron fluence was up to 1 × 1016 cm−2. On the one hand, the high neutron fluence of 1016 cm−2 resulted in a reduction in forward current density by two orders of magnitude and an extremely high on-resistance property due to the radiation-generated considerable series resistance in the SBD. On the other hand, the irradiation brought little influence on the Ni/β-Ga2O3 Schottky contact, since the extracted ideality factor and barrier height from temperature-dependent current–voltage (I–V–T) characteristics showed no significant changes after the radiation. Moreover, the capacitance–voltage (C–V) characterization revealed that the net carrier density in the β-Ga2O3 material was only reduced by 25% at the neutron fluence of 1015 cm−2 but a significant reduction by 2–3 orders at 1016 cm−2. Within the neutron fluence range of 2 × 1014 cm−2 up to 1016 cm−2, the carrier removal rates trended to be saturated with the increased fluences, following an exponential regular. In addition, the C–V measurement on the 1016 cm−2 irradiated sample exhibited an obvious frequency dispersion, and the extracted carrier distribution was not uniform.

Reversible Total Ionizing Dose Effects in NiO/Ga2O3 Heterojunction Rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1Mrad fluences of Co-60 g-rays either with or without reverse biases. While there is small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma-photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000x reduction in forward current and 100x increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on-off ratio is also reduced by almost 5 orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of < 4 cm-1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current-voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes. Figure 1

15 MeV proton damage in NiO/β-Ga2O3 vertical rectifiers

15 MeV proton irradiation of vertical geometry NiO/β-Ga2O3 heterojunction rectifiers produced reductions in reverse breakdown voltage from 4.3 kV to 3.7 kV for a fluence of 1013ions·cm−2 and 1.93 kV for 1014 ions·cm−2. The forward current density was also decreased by 1–2 orders of magnitude under these conditions, with associated increase in on-state resistance R ON. These changes are due to a reduction in carrier density and mobility in the drift region. The reverse leakage current increased by a factor of ∼2 for the higher fluence. Subsequent annealing up to 400 °C further increased reverse leakage due to deterioration of the contacts, but the initial carrier density of 2.2 × 1016 cm−3 was almost fully restored by this annealing in the lower fluence samples and by more than 50% in the 1014 cm−2 irradiated devices. Carrier removal rates in the Ga2O3 were in the range 190–1200 for the fluence range employed, similar to Schottky rectifiers without the NiO.

Carrier removal rates in 4H–SiC power diodes – A predictive analytical model

An analytical model for predicting the proton and neutron radiation-induced carrier removal in silicon carbide (4H–SiC) diodes, is developed. It is primarily aimed towards a fast calculation of the carrier removal rates (ηe) and critical fluence (above which the diode drift layer is fully compensated), for a wide range of particle energies and diode ratings. The model utilizes the NIEL (non-ionizing energy loss) concept along with the actual carrier removal rate values for SiC available in the literature. A comparison to Si power devices is also made. The results from the predictive model suggest that diodes with a lower voltage rating can sustain a higher particle fluence and displacement damage before their drift layers are fully compensated. This provides radiation hardening guidelines for 4H–SiC power diodes at a device engineering level, which can help improve the reliability of circuits in harsh environment applications, such as space. The model is validated through TCAD simulations incorporating the proton-induced defects, as well as experimentally by irradiating SiC diodes with 2 MeV protons. The extracted compensation levels are in good agreement with those predicted by the analytical model, validating its potential in predicting carrier removal rate of SiC diodes for radiation prone environments.

60Co γ-irradiation of AlGaN UVC light-emitting diodes

270 nm AlGaN UV Light-Emitting Diodes (LEDs) were exposed to 1–5 Mrad fluences of Co-60 γ-rays. The effect of the exposure to radiation was a ∼40% reduction in optical output after the highest fluence. No significant midgap emission was induced in the electro-luminescence spectra of the irradiated LEDs. We ascribe the decrease in optical output to creation of non-radiative states within the active regions. There were small (5–10%) increases in forward and reverse current as a result of irradiation with an effective carrier removal rate of <1 cm−1. The irradiation did not produce any increase in degradation rate of the LEDs output power under high drive current (95 mA) compared to unirradiated devices, which is consistent with the lack of midgap emission. The relatively small changes in electrical and optical properties, along with the resistance of the AlxGa1-xN/AlN to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications.

Reversible Total Ionizing Dose Effects in NiO/Ga2O3 Heterojunction Rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1Mrad fluences of Co-60 g-rays either with or without reverse biases. While there is small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma-photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000x reduction in forward current and 100x increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on-off ratio is also reduced by almost 5 orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of < 4 cm-1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current-voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

Carrier removal rates in 1.1 MeV proton irradiated α-Ga2O3 (Sn)

Films of α-Ga2O3 (Sn) grown by halide vapor phase epitaxy on sapphire with donor densities in the range 5 × 1015–8.4 × 1019 cm−3 were irradiated at 25 °C with 1.1 MeV protons to fluences from 1013 to 1016 cm−2. For the lowest doped samples, the carrier removal rate was ∼35 cm−1 at 1014 cm−2 and ∼1.3 cm−1 for 1015 cm−2 proton fluence. The observed removal rate could be accounted for by introduction of deep acceptors with optical ionization energies of 2 eV, 2.8 eV and 3.1 eV. For samples doped at 4 × 1018 cm−3, the initial electron removal rate was 5 × 103 cm−1 for 1015 cm−2 fluence and ∼300 cm−1 for 1016 cm−2 fluence. The same deep acceptors were observed in photocapacitance spectra, but their introduction rate was orders of magnitude lower than the carrier removal rate. For the heaviest doped samples, the electron removal rate was close to that for the 4 × 1018 cm−3 sample. The radiation tolerance of lightly doped α-Ga2O3 is higher than for similarly doped β-Ga2O3 layers.

Transport and trap states in proton irradiated ultra-thick κ-Ga2O3

Changes induced by irradiation with 1.1 MeV protons in the transport properties and deep trap spectra of thick (&amp;gt;80 μm) undoped κ-Ga2O3 layers grown on sapphire are reported. Prior to irradiation, the films had a donor concentration of ∼1015 cm−3, with the two dominant donors having ionization energies of 0.25 and 0.15 eV, respectively. The main electron traps were located at Ec−0.7 eV. Deep acceptor spectra measured by capacitance-voltage profiling under illumination showed optical ionization thresholds near 2, 2.8, and 3.4 eV. The diffusion length of nonequilibrium charge carriers for ɛ-Ga2O3 was 70 ± 5 nm prior to irradiation. After irradiation with 1.1 MeV protons to a fluence of 1014 cm−2, there was total depletion of mobile charge carriers in the top 4.5 μm of the film, close to the estimated proton range. The carrier removal rate was 10–20 cm−1, a factor of 5–10 lower than in β-Ga2O3, while the concentration of deep acceptors in the lower half of the bandgap and the diffusion length showed no significant change.

Electrical and Recombination Properties of Polar Orthorhombic κ-Ga2O3 Films Prepared by Halide Vapor Phase Epitaxy

In this study, the structural and electrical properties of orthorhombic κ-Ga2O3 films prepared using Halide Vapor Phase Epitaxy (HVPE) on AlN/Si and GaN/sapphire templates were studied. For κ-Ga2O3/AlN/Si structures, the formation of two-dimensional hole layers in the Ga2O3 was studied and, based on theoretical calculations, was explained by the impact of the difference in the spontaneous polarizations of κ-Ga2O3 and AlN. Structural studies indicated that in the thickest κ-Ga2O3/GaN/sapphire layer used, the formation of rotational nanodomains was suppressed. For thick (23 μm and 86 μm) κ-Ga2O3 films grown on GaN/sapphire, the good rectifying characteristics of Ni Schottky diodes were observed. In addition, deep trap spectra and electron beam-induced current measurements were performed for the first time in this polytype. These experiments show that the uppermost 2 µm layer of the grown films contains a high density of rather deep electron traps near Ec - 0.3 eV and Ec - 0.7 eV, whose presence results in the relatively high series resistance of the structures. The diffusion length of the excess charge carriers was measured for the first time in κ-Ga2O3. The film with the greatest thickness of 86 μm was irradiated with protons and the carrier removal rate was about 10 cm-1, which is considerably lower than that for β-Ga2O3.

Impact of neutron irradiation on electronic carrier transport properties in Ga2O3 and comparison with proton irradiation effects

The minority charge carrier transport in beta gallium oxide (-Ga2O3) before and after exposure to neutrons from a 241Am-Be source was studied. Cathodoluminescence (CL) spectroscopy and current–voltage (I-V) characteristics were used to study minority carrier behavior. High energy radiation affects minority carrier properties through the production of carrier traps that reduce the conductivity and mobility of the material. In this paper, we report the effects of neutron radiation in silicon-doped -Ga2O3, using rectifiers or transistors as the measurement platform. The thermal activation energy of the reference (non-irradiated) sample was 40.9 meV, which is ascribed to silicon-donors. CL measurements indicate a slightly indirect bandgap energy of 4.9 eV. Neutrons create disordered regions in -Ga2O3 rather than just point defects, resulting in the lowest carrier removal rate because of the lowest average non-ionizing energy loss. The neutron irradiation caused an increase in reverse bias leakage current in rectifiers and a carrier removal rate of 480 cm−1 but had little effect on reverse recovery switching time. Differences in CL spectra were observed between vertical and lateral device structures, emphasizing the importance of impurities and defects in the starting material. The neutron energies in the Am-Be source range up to 11 MeV, with an average energy between 4 and 5 MeV (Figure 1). We also contrasted neutron damage with the effects of irradiation with 10 MeV protons. Under 10 MeV proton irradiation, the thermal activation energies increase. This is attributable to high order defects and their influence on carrier lifetimes. The measurements show that -Ga2O3 is more resistant to radiation damage than other wide bandgap semiconductors due to its higher displacement threshold energy, which is inversely proportional to the lattice constant.

Proton radiation effects on electronic defect states in MOCVD-grown (010) β-Ga2O3

The impact of 1.8 MeV proton irradiation on metalorganic chemical vapor deposition grown (010) β-Ga2O3 Schottky diodes is presented. It is found that after a 10.8×1013cm−2 proton fluence the Schottky barrier height of (1.40±0.05 eV) and the ideality factor of (1.05±0.05) are unaffected. Capacitance–voltage extracted net ionized doping curves indicate a carrier removal rate of 268±10cm−1. The defect states responsible for the observed carrier removal are studied through a combination of deep level transient and optical spectroscopies (DLTS/DLOS) as well as lighted capacitance–voltage (LCV) measurements. The dominating effect on the defect spectrum is due to the EC-2.0 eV defect state observed in DLOS and LCV. This state accounts for ∼75% of the total trap introduction rate and is the primary source of carrier removal from proton irradiation. Of the DLTS detected states, the EC-0.72 eV state dominated but had a comparably smaller contribution to the trap introduction. These two traps have previously been correlated with acceptor-like gallium vacancy-related defects. Several other trap states at EC-0.36, EC-0.63, and EC-1.09 eV were newly detected after proton irradiation, and two pre-existing states at EC-1.2 and EC-4.4 eV showed a slight increase in concentration after irradiation, together accounting for the remainder of trap introduction. However, a pre-existing trap at EC-0.40 eV was found to be insensitive to proton irradiation and, therefore, is likely of extrinsic origin. The comprehensive defect characterization of 1.8 MeV proton irradiation damage can aid the modeling and design for a range of radiation tolerant devices.

Reversible total ionizing dose effects in NiO/Ga2O3 heterojunction rectifiers

NiO/Ga2O3 heterojunction rectifiers were exposed to 1 Mrad fluences of Co-60 γ-rays either with or without reverse biases. While there is a small component of Compton electrons (600 keV), generated via the interaction of 1.17 and 1.33 MeV gamma photons with the semiconductor, which in turn can lead to displacement damage, most of the energy is lost to ionization. The effect of the exposure to radiation is a 1000× reduction in forward current and a 100× increase in reverse current in the rectifiers, which is independent of whether the devices were biased during this step. The on–off ratio is also reduced by almost five orders of magnitude. There is a slight reduction in carrier concentration in the Ga2O3 drift region, with an effective carrier removal rate of &amp;lt;4 cm−1. The changes in electrical characteristics are reversible by application of short forward current pulses during repeated measurement of the current–voltage characteristics at room temperature. There are no permanent total ionizing dose effects present in the rectifiers to 1 Mad fluences, which along with their resistance to displacement damage effects indicate that these devices may be well-suited to harsh terrestrial and space radiation applications if appropriate bias sequences are implemented to reverse the radiation-induced changes.

Features of the Carrier Concentration Determination during Irradiation of Wide-Gap Semiconductors: The Case Study of Silicon Carbide

In this paper, the features of radiation compensation of wide-gap semiconductors are discussed, considering the case study of silicon carbide. Two classical methods of concentration determination are compared and analyzed: capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The dependence of the base resistance in high-voltage 4H-SiC Schottky diodes on the dose of irradiation by electrons and protons is experimentally traced in the range of eight orders of magnitude. It is demonstrated that the dependence of the carrier concentration on the irradiation dose can be determined unambiguously and reliably in a very wide range of compensation levels, based on the results of measuring the I-V characteristics. It is shown that the determination of the carrier removal rate using the I-V characteristics is more correct than using the C-V characteristics, especially in the case of high radiation doses.

1 GeV proton damage in β-Ga2O3

The changes of electrical properties and deep trap spectra induced in n-type β-Ga2O3 by 1 GeV protons with a fluence of 4 × 1013 cm−2 were studied. The carrier removal rates were ∼100 cm−1 at this energy. For comparison, for 20 MeV proton irradiation at comparable fluences (5–10 × 1014 cm−2), the removal rate was ∼400 cm−1 for donor concentrations of 3 × 1016 cm−3 and ∼100 cm−1 for concentrations of &amp;lt;1016 cm−3. These removal rates were in stark contrast with modeling results that predicted the introduction rates of vacancies to be two orders of magnitude higher for 20 MeV protons. Measurements of deep electron and hole traps densities by deep level transient spectroscopy with electrical or optical injection (DLTS or ODLTS), and capacitance–voltage profiling under monochromatic light illumination showed that the 1 GeV proton irradiation resulted in the introduction of deep donors E2*(Ec-0.75 eV) and E3 (Ec-1 eV) and deep acceptors with optical ionization threshold near 2.3 eV producing a feature near 250 K in ODLTS and 3.1 eV with related ODLTS feature near 450 K. The total concentration of all deep traps was much lower than that necessary to explain the observed decrease in net donor density upon irradiation. The donor densities showed a nonuniform distribution in proton irradiated films with the concentration greatly decreased toward the surface. Possible reasons for the observed performance are discussed.

Radiation Hardness of Silicon Carbide upon High-Temperature Electron and Proton Irradiation.

The radiation hardness of silicon carbide with respect to electron and proton irradiation and its dependence on the irradiation temperature are analyzed. It is shown that the main mechanism of SiC compensation is the formation of deep acceptor levels. With increasing the irradiation temperature, the probability of the formation of these centers decreases, and they are partly annealed out. As a result, the carrier removal rate in SiC becomes ~6 orders of magnitude lower in the case of irradiation at 500 °C. Once again, this proves that silicon carbide is promising as a material for high-temperature electronics devices.

Degradation of β-Ga2O3 Schottky barrier diode under swift heavy ion irradiation* *Project supported by the National Natural Science Foundation of China (Grant Nos. 12035019, 11690041, and 12075290), China National Postdoctoral Program for Innovative Talents (Grant No. BX20200340), China Postdoctoral Science Foundation (Grant No. 2020M673539), CAS “Light of West China” Program, and the Youth Innovation Promotion Association of Chinese Academy of

The electrical characteristics and microstructures of β-Ga2O3 Schottky barrier diode (SBD) devices irradiated with swift heavy ions (2096 MeV Ta ions) have been studied. It was found that β-Ga2O3 SBD devices showed the reliability degradation after irradiation, including turn-on voltage V on, on-resistance R on, ideality factor n, and the reverse leakage current density J r. In addition, the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5 × 106–1.3 × 107 cm−1. Latent tracks induced by swift heavy ions were observed visually in the whole β-Ga2O3 matrix. Furthermore, crystal structure of tracks was amorphized completely. The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration. Eventually, these defects caused the degradation of electrical characteristics of the devices. In terms of the carrier removal rates, the β-Ga2O3 SBD devices were more sensitive to swift heavy ions irradiation than SiC and GaN devices.

Pulsed fast reactor neutron irradiation effects in Si doped n-type β-Ga2O3

The effects of pulsed neutron irradiation on Si doped n-type β-Ga2O3 films grown by halide vapor phase epitaxy (HVPE) on bulk Sn doped n+ β-Ga2O3 substrates are reported. This irradiation leads to an almost linear increase with neutron fluence of the density of deep electron traps E2* (Ec − 0.74 eV), E3 (Ec − 1.05 eV), and E4 (Ec − 1.2 eV), with an introduction rate close to 0.4–0.6 cm−1 while the density of the E2 traps (Ec − 0.8 eV) related to Fe was virtually unchanged. In addition, the increase in the density of deep traps with optical ionization threshold of 1.3 eV, 2.3 eV, and 3.1 eV with an introduction rate close to 0.8–2 cm−1 was observed. The carrier removal rate under our conditions was 28 cm−1. Neutron irradiation also led to a measurable decrease of the diffusion length of nonequilibrium charge carriers. The results are qualitatively similar to previous reports for proton and α-particle irradiation of HVPE β-Ga2O3. When comparing the findings with those described earlier for bulk neutron irradiated Ga2O3, we observe lower starting densities of electron and hole traps and lower introduction rates for these traps in the epitaxial structures. The carrier removal rates were comparable to those in bulk crystals.

Alpha Particle Irradiation of High Aluminum Content AlGan Polarization Doped Field Effect Transistors

Alpha particle irradiation at 18 MeV was performed on high aluminum content AlGaN Polarization Doped Field Effect Transistors (POLFTs) and characterized by DC and switching measurements. The POLFETs underwent a reduction in DC saturation current of 23% and 33% at fluences of 1 × 1013 cm−2 and 3 × 1013 cm−2, respectively. Carrier removal rates in the range of 2520 cm−1 and 7100 cm−1 were observed, which are similar to previously reported values for GaN HEMTs. The POLFETs under 100 kHz gate lag measurement demonstrated zero degradation while compared to a traditional GaN HEMT device which suffered serious current collapse as a result of formation of a virtual gate from radiation-induced defects.