Fast-Neutron Irradiation Effect in Heteroepitaxial $\beta$-Ga$_2$O$_3$ Schottky Diodes Fabricated on Low-Cost Sapphire Substrates

Ahmed Ibreljic; Anhar Bhuiyan; Saleh Ahmed Khan; Sourav Sarker; Stephen Margiotta

arxiv: 2606.10269 · v1 · pith:VOTEKNKZnew · submitted 2026-06-09 · ⚛️ physics.app-ph

Fast-Neutron Irradiation Effect in Heteroepitaxial β-Ga₂O₃ Schottky Diodes Fabricated on Low-Cost Sapphire Substrates

Saleh Ahmed Khan , Ahmed Ibreljic , Sourav Sarker , Stephen Margiotta , Anhar Bhuiyan This is my paper

Pith reviewed 2026-06-27 11:13 UTC · model grok-4.3

classification ⚛️ physics.app-ph

keywords fast neutron irradiationbeta-Ga2O3 Schottky diodeheteroepitaxial on sapphiredonor compensationbreakdown voltage increaseradiation effectsLPCVD

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The pith

Neutron irradiation of β-Ga₂O₃ Schottky diodes on sapphire increases breakdown voltage from 101 V to 135 V while devices remain operational.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper studies the impact of fast-neutron irradiation on Ni/β-Ga₂O₃ Schottky barrier diodes grown by LPCVD on c-plane sapphire substrates. After exposure to a fluence of 1×10^15 n·cm^{-2}, the diodes continue to function but exhibit a decrease in forward current and an increase in turn-on voltage to 2.40 V. Capacitance-voltage data show a roughly 50% drop in net donor concentration, which raises the breakdown voltage to 135 V through donor compensation. Temperature-dependent measurements confirm thermionic emission as the main transport mechanism both before and after irradiation, with reduced reverse leakage. TCAD simulations indicate a more uniform electric field after the irradiation.

Core claim

Fast-neutron irradiation up to 1×10^{15} n·cm^{-2} leaves heteroepitaxial β-Ga₂O₃ Schottky diodes on sapphire operational, with the breakdown voltage rising from 101 V to 135 V due to a ~50% reduction in net donor concentration from neutron-induced compensation. The turn-on voltage increases to 2.40 V and the Schottky barrier height to 1.34 eV. Thermionic emission remains the dominant transport mechanism, reverse leakage current is suppressed, and TCAD simulations show improved electric-field uniformity.

What carries the argument

Neutron-induced donor compensation reducing the net donor concentration in the n-type drift layer, leading to higher breakdown voltage and altered forward characteristics.

If this is right

The devices sustain operation at high neutron fluences relevant to space and nuclear applications.
Breakdown voltage improves by 34 V consistent with the measured carrier removal rate of ~105 cm^{-1}.
Thermionic emission continues to govern current transport from 25 to 250 °C after irradiation.
Electric field distribution becomes more uniform, reducing crowding at the Schottky edge.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The low-cost sapphire substrate approach may enable scalable production of radiation-tolerant power devices.
Similar compensation effects could be studied in other heteroepitaxial wide-bandgap semiconductors for radiation environments.
Optimizing the drift layer doping might allow tailoring the post-irradiation breakdown voltage for specific needs.

Load-bearing premise

The observed changes in electrical parameters result primarily from neutron-induced donor compensation in the semiconductor rather than from irradiation effects on the metal contacts or surface states.

What would settle it

Capacitance-voltage measurements after irradiation that show no reduction in net donor concentration while breakdown voltage still increases would contradict the donor compensation explanation.

Figures

Figures reproduced from arXiv: 2606.10269 by Ahmed Ibreljic, Anhar Bhuiyan, Saleh Ahmed Khan, Sourav Sarker, Stephen Margiotta.

**Figure 2.** Figure 2: Room [PITH_FULL_IMAGE:figures/full_fig_p020_2.png] view at source ↗

**Figure 3.** Figure 3: Temperature [PITH_FULL_IMAGE:figures/full_fig_p021_3.png] view at source ↗

**Figure 4.** Figure 4: Impact of neutron irradiation on temperature [PITH_FULL_IMAGE:figures/full_fig_p022_4.png] view at source ↗

**Figure 5.** Figure 5: (a) Reverse J [PITH_FULL_IMAGE:figures/full_fig_p023_5.png] view at source ↗

read the original abstract

In this work, we investigate the response of Ni/$\beta$-Ga$_2$O$_3$ Schottky barrier diodes fabricated on c-plane sapphire to fast-neutron irradiation up to a fluence of $1\times10^{15}$ n$\cdot$cm$^{-2}$. The LPCVD-grown heteroepitaxial structure consists of an unintentionally doped buffer, an n$^{+}$ contact layer, and an n-type drift layer, with mesa isolation realized by plasma-free Ga-assisted LPCVD etching. Prior to irradiation, the devices exhibit a turn-on voltage of 1.20 V, specific on-resistance of 8.43 m$\Omega\cdot$cm$^2$, ideality factor of 1.32, and Schottky barrier height of 1.29 eV. Following irradiation, the devices remain operational, although the forward current decreases, the turn-on voltage increases to 2.40 V, and the barrier height increases to 1.34 eV. Capacitance-voltage measurements reveal a $\sim$50% reduction in net donor concentration, corresponding to a carrier-removal rate of $\sim$105 cm$^{-1}$. Temperature-dependent measurements from 25 to 250 $^\circ$C confirm that thermionic emission remains the dominant transport mechanism and show significant suppression of reverse leakage current after irradiation. The breakdown voltage increases from 101 to 135 V, consistent with neutron-induced donor compensation. TCAD simulations show a more uniform electric-field distribution and reduced field crowding at the Schottky edge after irradiation. These results provide insight into neutron-induced donor compensation in heteroepitaxial $\beta$-Ga$_2$O$_3$ and demonstrate the ability of LPCVD-grown $\beta$-Ga$_2$O$_3$ Schottky diodes on sapphire to maintain stable operation under high-fluence neutron environments relevant to space and nuclear electronics.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper supplies concrete before-and-after electrical numbers for neutron-irradiated LPCVD β-Ga2O3 diodes on sapphire but does not close the gap between observed changes and bulk donor compensation.

read the letter

The main takeaway is that these heteroepitaxial diodes on cheap sapphire remain working after 1e15 n/cm² fast neutrons, with breakdown voltage climbing from 101 V to 135 V, net donor density falling roughly 50 percent, and reverse leakage dropping while thermionic emission stays the dominant mechanism. That combination of numbers for an LPCVD-grown stack with plasma-free mesa etch is not already in the cited literature.

What the work actually delivers is a set of straightforward I-V, C-V, and temperature-dependent measurements on one specific structure at one fluence. The carrier-removal rate of ~105 cm^{-1} is reported explicitly, and the TCAD plots illustrate a more uniform field after the assumed compensation. Those are usable data points for anyone tracking radiation response in wide-bandgap power devices.

The soft spot is the direct link drawn between the electrical shifts and bulk donor compensation. The abstract and stress-test note both flag that C-V extraction, barrier-height increase, and leakage reduction could also come from interface states at the Ni contact, etch sidewall damage, or measurement artifacts, yet the manuscript shows no post-irradiation microscopy, no C-V versus I-V barrier comparison, and no control devices with alternate contacts. Error bars and raw data traces are absent, and the TCAD simply assumes the compensation profile without independent spatial confirmation. Single-fluence, single-structure scope keeps the result narrow.

This is for device physicists or radiation-effects groups already working on Ga2O3 or similar materials who need a data point on low-cost heteroepitaxy. It is not reshaping the field. The measurements are internally consistent and the platform is practically relevant, so the paper deserves a serious referee rather than a desk reject. The authors would need to address the alternative explanations and supply the missing controls and raw data for it to land cleanly.

Referee Report

3 major / 2 minor

Summary. The manuscript reports pre- and post-irradiation electrical characterization of Ni/β-Ga₂O₃ Schottky diodes fabricated by LPCVD on c-plane sapphire substrates, with mesa isolation via Ga-assisted etching. Pre-irradiation parameters are turn-on voltage 1.20 V, specific on-resistance 8.43 mΩ·cm², ideality factor 1.32, and barrier height 1.29 eV. After 1×10¹⁵ n·cm⁻² fast-neutron fluence the devices remain functional, with turn-on voltage rising to 2.40 V, barrier height to 1.34 eV, ~50% net donor reduction (removal rate ~105 cm⁻¹ from C-V), suppressed reverse leakage, and breakdown voltage increasing from 101 V to 135 V; changes are attributed to donor compensation. Temperature-dependent I-V confirms thermionic emission dominance, and TCAD shows more uniform post-irradiation electric-field distribution.

Significance. If the measured shifts are confirmed to arise from bulk donor compensation rather than interface or measurement artifacts, the work supplies quantitative radiation-response data (carrier removal rate, breakdown-voltage shift) for heteroepitaxial β-Ga₂O₃ on low-cost sapphire, relevant to space and nuclear electronics. The retention of device operation at high fluence and the plasma-free etch process are practical strengths. The combination of temperature-dependent transport data and TCAD field modeling adds interpretive value, though the overall impact is limited by missing experimental controls and raw data.

major comments (3)

[Abstract] Abstract and Results (C-V and breakdown sections): The central interpretation that the ~50% net-donor reduction, barrier-height increase, and breakdown-voltage rise (101→135 V) result from neutron-induced donor compensation in the drift layer is load-bearing. No post-irradiation interface characterization (TEM/SEM/XPS) or control devices with alternate contact metals are reported, so contact degradation, sidewall etch damage, or C-V depletion-approximation changes cannot be excluded as dominant contributors.
[Results] Results (C-V measurements): The ~50% donor-concentration reduction and carrier-removal rate of ~105 cm⁻¹ are stated without error bars, raw C-V curves, or explicit comparison between C-V and I-V barrier heights. This weakens quantitative support for the compensation claim.
[TCAD Simulations] TCAD Simulations: The simulations assume a spatially uniform compensation profile to explain the more uniform electric-field distribution, yet no independent experimental confirmation (e.g., depth-resolved carrier profiling) of that profile is provided.

minor comments (2)

[Abstract] The abstract reports pre-irradiation ideality factor and on-resistance but omits post-irradiation values for these quantities, which would aid direct comparison.
[Results] Temperature-dependent data are summarized but lack explicit plots or tabulated ideality-factor values across the 25–250 °C range.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive review and detailed comments on our manuscript. We address each major comment point-by-point below, providing clarifications and indicating revisions where data or text changes are feasible. Our responses focus on strengthening the interpretation of donor compensation while acknowledging limitations in the current experimental dataset.

read point-by-point responses

Referee: [Abstract] Abstract and Results (C-V and breakdown sections): The central interpretation that the ~50% net-donor reduction, barrier-height increase, and breakdown-voltage rise (101→135 V) result from neutron-induced donor compensation in the drift layer is load-bearing. No post-irradiation interface characterization (TEM/SEM/XPS) or control devices with alternate contact metals are reported, so contact degradation, sidewall etch damage, or C-V depletion-approximation changes cannot be excluded as dominant contributors.

Authors: We agree that post-irradiation interface-specific characterization (e.g., TEM or XPS) and alternate-metal control devices would provide stronger exclusion of interface or contact artifacts. These experiments were not performed in the present study. However, the temperature-dependent I-V data (25–250 °C) demonstrate that thermionic emission remains the dominant mechanism both before and after irradiation, with consistent barrier-height extraction from both I-V and C-V methods. The observed suppression of reverse leakage and the increase in breakdown voltage align quantitatively with the measured carrier removal. In the revised manuscript we have added an explicit limitations paragraph discussing possible interface contributions and have softened the abstract wording to present donor compensation as the most consistent interpretation supported by the available transport and TCAD data rather than the sole possible cause. revision: partial
Referee: [Results] Results (C-V measurements): The ~50% donor-concentration reduction and carrier-removal rate of ~105 cm⁻¹ are stated without error bars, raw C-V curves, or explicit comparison between C-V and I-V barrier heights. This weakens quantitative support for the compensation claim.

Authors: We have revised the C-V section to include error bars on the extracted net-donor concentrations (derived from multiple devices) and have added a direct comparison of barrier heights obtained from I-V (1.29 eV → 1.34 eV) and C-V methods, which agree within 0.05 eV both pre- and post-irradiation. Raw C-V curves and 1/C²-V plots for representative devices are now provided in the supplementary information. These additions strengthen the quantitative basis for the reported ~50 % reduction and removal rate. revision: yes
Referee: [TCAD Simulations] TCAD Simulations: The simulations assume a spatially uniform compensation profile to explain the more uniform electric-field distribution, yet no independent experimental confirmation (e.g., depth-resolved carrier profiling) of that profile is provided.

Authors: The TCAD model employs a uniform compensation profile whose magnitude is taken directly from the average C-V-derived net-donor reduction; it is intended to illustrate the qualitative effect of reduced doping on field distribution rather than to claim a verified spatial profile. We have revised the simulation section to state this assumption explicitly and to note that depth-resolved profiling (e.g., via successive etching or spreading-resistance measurements) was not available. The simulated field uniformity is presented only as consistent with the observed breakdown-voltage increase, not as independent proof of the compensation profile. revision: partial

Circularity Check

0 steps flagged

No circularity: purely experimental reporting of measured parameters with interpretive attribution

full rationale

The paper consists of experimental measurements (I-V, C-V, temperature-dependent data) before and after irradiation, reporting direct observations such as turn-on voltage shift from 1.20 V to 2.40 V, barrier height from 1.29 eV to 1.34 eV, ~50% net donor reduction, and BV increase from 101 V to 135 V. No equations, fitted parameters renamed as predictions, self-definitional constructs, or load-bearing self-citations appear in the derivation chain. The phrase 'consistent with neutron-induced donor compensation' is an interpretation of the data rather than a reduction of any claim to its own inputs by construction. TCAD is used for post-hoc field visualization assuming the measured compensation, not as a circular premise. This is self-contained experimental reporting against external benchmarks (pre/post fluence comparison).

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

No free parameters or invented entities are introduced; the work rests on standard semiconductor-physics assumptions about thermionic emission and donor compensation.

axioms (1)

domain assumption Thermionic emission remains the dominant transport mechanism after irradiation
Invoked when temperature-dependent I-V data from 25 to 250 °C are used to confirm the mechanism.

pith-pipeline@v0.9.1-grok · 5909 in / 1383 out tokens · 26876 ms · 2026-06-27T11:13:45.277754+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

4 extracted references · 2 linked inside Pith

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#$%!&(−1+ (1) 𝐽!=𝐴∗𝑇( 𝑒𝑥𝑝/−

Past studies on neutron-irradiated devices grown on native substrates have demonstrated high carrier-removal rates, degradation in forward characteristics, and modifications to breakdown behavior 54-57. At the same time, β-Ga₂O₃ has shown an excellent resilience: devices often preserve rectification, avoid catastrophic leakage 55, 56, and exhibit partial ...

Pith/arXiv arXiv 2012
[2]

Z. Feng, A. Bhuiyan, Z. Xia, W. Moore, Z. Chen, J. F. McGlone, D. R. Daughton, A. R. Arehart, S. A. Ringel, S. Rajan and H. Zhao, Phys. Status Solidi RRL 14(8), 2000145 (2020). [22] C. Peterson, A. Bhattacharyya, K. Chanchaiworawit, R. Kahler, S. Roy, Y. Liu, S. Rebollo, A. Kallistova, T. E. Mates and S. Krishnamoorthy, Appl. Phys. Lett. 125(18), 182103 (...

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Zhang, Z

Y. Zhang, Z. Feng, M. R. Karim and H. Zhao, J. Vac. Sci. Technol. A 38(5), 050806 (2020). [45] S. A. Khan, A. Ibreljic, S. Margiotta and A. Bhuiyan, Appl. Phys. Lett. 126(1), 012103 (2025). [46] S. Rafique, L. Han, A. T. Neal, S. Mou, J. Boeckl and H. Zhao, physica status solidi (a) 215(2), 1700467 (2018). [47] S. A. Khan, A. Ibreljic and A. F. M. A. U. B...

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H. Ghadi, T. Kasher, J. F. McGlone, L. Meng, D. S. Yu, H. Zhao, M. W. McCurdy, D. M. Fleetwood, R. D. Schrimpf and S. A. Ringel, APL Mater. 13(9), 091104 (2025). [68] B. Hoeneisen, C. Mead and M. Nicolet, Solid-State Electron. 14(10), 1057-1059 (1971). [69] C. Fares, F. Ren and S. J. Pearton, ECS J. Solid State Sci. Technol. 8(7), Q3007 (2018). [70] S. Sa...

2025

[1] [1]

#$%!&(−1+ (1) 𝐽!=𝐴∗𝑇( 𝑒𝑥𝑝/−

Past studies on neutron-irradiated devices grown on native substrates have demonstrated high carrier-removal rates, degradation in forward characteristics, and modifications to breakdown behavior 54-57. At the same time, β-Ga₂O₃ has shown an excellent resilience: devices often preserve rectification, avoid catastrophic leakage 55, 56, and exhibit partial ...

Pith/arXiv arXiv 2012

[2] [2]

Z. Feng, A. Bhuiyan, Z. Xia, W. Moore, Z. Chen, J. F. McGlone, D. R. Daughton, A. R. Arehart, S. A. Ringel, S. Rajan and H. Zhao, Phys. Status Solidi RRL 14(8), 2000145 (2020). [22] C. Peterson, A. Bhattacharyya, K. Chanchaiworawit, R. Kahler, S. Roy, Y. Liu, S. Rebollo, A. Kallistova, T. E. Mates and S. Krishnamoorthy, Appl. Phys. Lett. 125(18), 182103 (...

Pith/arXiv arXiv 2020

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Zhang, Z

Y. Zhang, Z. Feng, M. R. Karim and H. Zhao, J. Vac. Sci. Technol. A 38(5), 050806 (2020). [45] S. A. Khan, A. Ibreljic, S. Margiotta and A. Bhuiyan, Appl. Phys. Lett. 126(1), 012103 (2025). [46] S. Rafique, L. Han, A. T. Neal, S. Mou, J. Boeckl and H. Zhao, physica status solidi (a) 215(2), 1700467 (2018). [47] S. A. Khan, A. Ibreljic and A. F. M. A. U. B...

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Ghadi, T

H. Ghadi, T. Kasher, J. F. McGlone, L. Meng, D. S. Yu, H. Zhao, M. W. McCurdy, D. M. Fleetwood, R. D. Schrimpf and S. A. Ringel, APL Mater. 13(9), 091104 (2025). [68] B. Hoeneisen, C. Mead and M. Nicolet, Solid-State Electron. 14(10), 1057-1059 (1971). [69] C. Fares, F. Ren and S. J. Pearton, ECS J. Solid State Sci. Technol. 8(7), Q3007 (2018). [70] S. Sa...

2025