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arxiv: 2604.06359 · v1 · submitted 2026-04-07 · ❄️ cond-mat.mtrl-sci

Grafted Low-Leakage Si/AlN p-n Diodes Enabled by Fluorinated AlN Interface

Yi Lu , Tsung-Han Tsai , Qingxiao Wang , Haicheng Cao , Jie Zhou , You Jin Koo , Chenyu Wang , Yang Liu
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Yueyue Hao Michael Eller Connor Bailey Stephanie Liu Nicholas J. Tanen Zhiyuan Liu Mingtao Nong Robert M. Jacobberger Tien Khee Ng Katherine Fountaine Vincent Gambin Boon S. Ooi Xiaohang Li Zhenqiang Ma
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Pith reviewed 2026-05-10 18:40 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords AlNp-n diodeinterface engineeringfluorinationleakage currentheterojunctionsurface passivationgrafting
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The pith

AlFx/SiNx interface on cleaned AlN reduces reverse leakage in grafted Si/AlN diodes by several orders of magnitude.

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

The paper establishes an interface engineering method for AlN that starts with low-damage etching to strip away defective oxides formed during high-temperature contact annealing, followed by XeF2 exposure to create an ultrathin AlFx layer and then ALD SiNx capping. This stack is used before grafting a p-type silicon nanomembrane to form the heterojunction. Electrical data show the treated diodes have far lower reverse currents than controls while forward characteristics remain intact, with temperature studies indicating that Poole-Frenkel emission is suppressed so leakage is now set by bulk crystal quality instead of the surface.

Core claim

The central claim is that forming an ultrathin AlFx layer via XeF2 on a restored near-stoichiometric AlN surface and stabilizing it with a thin SiNx cap suppresses defect-assisted reverse leakage in p-Si/n-AlN grafted diodes by several orders of magnitude relative to untreated or simply oxide-removed surfaces, while forward conduction is preserved; XPS and TEM confirm Al-F bond formation, lowered Al-O content, and an interfacial SiOx/SiON layer, with the leakage mechanism shifting from interface emission to bulk AlN limits.

What carries the argument

The AlFx/SiNx passivation bilayer created by XeF2 fluorination and ALD SiNx after pseudo-atomic-layer oxide removal, which blocks defect paths and suppresses Poole-Frenkel emission at the grafted heterojunction.

If this is right

  • Low-leakage ultrawide-bandgap AlN heterojunction diodes become feasible for power electronics once surface oxides are managed.
  • The grafting technique can now be applied to AlN without the previous penalty from RTA-induced surface damage.
  • Further gains in diode performance will depend on improving AlN crystal quality rather than interface fixes.
  • High-temperature contact formation on n-AlN can be used without destroying heterojunction rectifying behavior.

Where Pith is reading between the lines

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

  • The same fluorination-plus-nitride-cap sequence could stabilize surfaces in other reactive wide-bandgap materials that suffer from oxide formation during processing.
  • If bulk AlN quality improves independently, these interface-treated diodes could reach even lower leakage floors set by intrinsic material limits.
  • The approach may allow reliable integration of AlN with additional semiconductor layers via grafting for more complex power or RF devices.

Load-bearing premise

Leakage reduction is caused by the AlFx/SiNx layer suppressing Poole-Frenkel emission, assuming the grafting process and bulk AlN quality stay the same across samples and that XeF2 or ALD steps do not create new defects.

What would settle it

Fabricating control diodes with identical grafting and annealing but without the XeF2 fluorination step and finding no difference in reverse leakage current, or observing higher leakage after the full process in some batches, would show the interface engineering is not responsible for the improvement.

Figures

Figures reproduced from arXiv: 2604.06359 by Boon S. Ooi, Chenyu Wang, Connor Bailey, Haicheng Cao, Jie Zhou, Katherine Fountaine, Michael Eller, Mingtao Nong, Nicholas J. Tanen, Qingxiao Wang, Robert M. Jacobberger, Stephanie Liu, Tien Khee Ng, Tsung-Han Tsai, Vincent Gambin, Xiaohang Li, Yang Liu, Yi Lu, You Jin Koo, Yueyue Hao, Zhenqiang Ma, Zhiyuan Liu.

Figure 2
Figure 2. Figure 2: (a) Illustration of fluorination process on AlN surface; Al 2p spectra of AlN surface after XeF2 treatment of (b-1) 10 cycles, (b-2) 30 cycles, and (b-3) 60 cycles; (c) extracted atomic ratio of Al 2p-N, N 1s, F 1s under different XeF2 treatment conditions. After removal of the thermal oxide, XeF₂ treatment was applied to modify the chemical state of the AlN surface. As illustrated in Figure 2a, this proce… view at source ↗
Figure 3
Figure 3. Figure 3: (a) Fabrication flow of Sample A, B, C; (b) Microscope images during the fabrication process for Sample C; typical IV curves of (c) Sample A (d) Sample B and (e) Sample C (five devices for each). Using the three types of AlN surfaces described above: Sample A: thermal-oxide interface; Sample B: pseudo-ALE-treated interface with minimized surface oxide; Sample C: AlFx/SiNx interface; p-Si/n￾AlN heterojuncti… view at source ↗
Figure 4
Figure 4. Figure 4: (a) Extracted reverse-bias current at -20 V, (b) on/off current ratio (at ±20 V), and (c) specific on￾resistance (RON) of Samples A–C. (d) Temperature-dependent I–V characteristics of Sample C measured from room temperature (RT) to 100 °C. (e) Arrhenius plot of reverse current density (Jr) as a function of 1/kT. (f) ln(Jr) plotted as a function of 1/E, illustrating the field-dependent transport behavior at… view at source ↗
Figure 5
Figure 5. Figure 5: (a) XPS Al 2p and (b) Si 2p core-level spectra acquired at the Si/AlN interface of Sample C. (c) Reconstructed band alignment of the Si/AlN heterojunction based on the XPS analysis. (d) Cross-sectional transmission electron microscopy (TEM) image of the Si/AlN interface. (e) Corresponding energy￾dispersive X-ray spectroscopy (EDS) elemental maps of the Si/AlN interface. (f) Schematic illustration of the Si… view at source ↗
read the original abstract

Ultrawide-bandgap AlN is a promising material for next-generation power electronics; however, its practical implementation is hindered by unstable surface chemistry and the high activation energy of p-type dopants. In particular, high-temperature rapid thermal annealing (RTA), required for forming low-resistance contacts on n-type AlN, leads to the formation of thick and defective surface oxides that degrade heterojunction performance. In this work, we present an interface engineering approach based on fluorination-induced AlFx formation combined with SiNx passivation to suppress defect-assisted leakage in p-Si/n-AlN heterojunction diodes fabricated via semiconductor grafting. A low-damage pseudo-atomic layer etching process is employed to remove RTA-induced oxides and restore a near-stoichiometric AlN surface. Subsequent XeF2 treatment forms an ultrathin AlFx layer, which is stabilized by an atomic-layer-deposited SiNx capping layer prior to p-Si nanomembrane integration. Electrical measurements show that the engineered AlFx/SiNx interface reduces reverse leakage current by several orders of magnitude compared to untreated or oxide-removed AlN surfaces, while preserving forward conduction characteristics. Temperature-dependent analysis indicates strong suppression of Poole-Frenkel emission and a shift of leakage onset to higher reverse bias, ultimately limited by bulk AlN crystal quality. X-ray photoelectron spectroscopy and transmission electron microscopy confirm the formation of Al-F bonds, reduced Al-O content, and the presence of a thin interfacial SiOx/SiON layer. These results establish AlFx/SiNx passivation as an effective strategy for stabilizing AlN interfaces and enabling low-leakage ultrawide-bandgap heterojunction devices.

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.

Referee Report

1 major / 1 minor

Summary. The paper claims that a fluorinated AlFx/SiNx interface, formed via low-damage pseudo-ALE oxide removal, XeF2 treatment, and ALD SiNx capping on RTA-processed AlN, enables low-leakage p-Si/n-AlN heterojunction diodes by semiconductor grafting. Electrical I-V data show reverse leakage reduced by several orders of magnitude relative to untreated or oxide-removed controls while forward characteristics are preserved; temperature-dependent measurements indicate Poole-Frenkel suppression with leakage ultimately bulk-limited. XPS confirms Al-F bonding and reduced Al-O, and TEM shows the thin interfacial layer.

Significance. If the central result holds, the work is significant for ultrawide-bandgap AlN power electronics: it directly addresses post-RTA surface oxide instability that has limited heterojunction performance and provides a practical passivation route compatible with grafting. The multi-modal characterization (electrical, XPS, TEM) and explicit link to Poole-Frenkel suppression add concrete value beyond prior surface treatments.

major comments (1)
  1. [Results section on electrical measurements] Results section on electrical measurements (abstract and I-V data): The claim that the AlFx/SiNx interface reduces reverse leakage by orders of magnitude and suppresses Poole-Frenkel emission rests on the assumption that grafting quality, effective area, and bulk AlN crystal quality are statistically equivalent across the compared surface treatments. No device-to-device statistics, number of measured devices, error bars, variability metrics, or same-wafer controls are reported, leaving open the possibility that observed differences partly reflect grafting variability or processing-induced defects rather than interface passivation alone. This is load-bearing for the central attribution.
minor comments (1)
  1. [Abstract] Abstract: The phrase 'several orders of magnitude' is used without quoting the actual current densities or the precise factor (e.g., 10^3 vs. 10^5) at a given bias; adding quantitative values would strengthen the claim.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their positive assessment of the significance of our work and for the constructive feedback on the electrical data presentation. We address the major comment below.

read point-by-point responses

  1. Referee: [Results section on electrical measurements] Results section on electrical measurements (abstract and I-V data): The claim that the AlFx/SiNx interface reduces reverse leakage by orders of magnitude and suppresses Poole-Frenkel emission rests on the assumption that grafting quality, effective area, and bulk AlN crystal quality are statistically equivalent across the compared surface treatments. No device-to-device statistics, number of measured devices, error bars, variability metrics, or same-wafer controls are reported, leaving open the possibility that observed differences partly reflect grafting variability or processing-induced defects rather than interface passivation alone. This is load-bearing for the central attribution.

    Authors: We agree that the absence of explicit statistical reporting in the current manuscript leaves the central attribution open to the interpretation raised by the referee. In the revised manuscript we will add device-to-device statistics for all surface-treatment conditions, including the number of devices measured, error bars on the I-V curves (standard deviation), and variability metrics such as the standard deviation of reverse leakage at a fixed bias. We will also clarify that the untreated, oxide-removed, and fluorinated samples were prepared on the same AlN wafer, with only the surface treatment differing, thereby controlling for grafting quality and bulk crystal quality. These additions will be incorporated into both the room-temperature and temperature-dependent data sets to reinforce that the leakage reduction and Poole-Frenkel suppression arise from the AlFx/SiNx interface. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental results with no derivations

full rationale

The paper reports fabrication of Si/AlN diodes via grafting, surface treatments (pseudo-ALE, XeF2 fluorination, ALD SiNx), and characterization by I-V measurements, temperature-dependent analysis, XPS, and TEM. No equations, models, predictions, or first-principles derivations appear in the abstract or described content. Claims of leakage reduction rest on direct comparisons of measured currents across surface conditions, not on any self-referential fitting, self-citation chains, or renamings. The work is self-contained against external benchmarks of experimental reproducibility.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental paper with no mathematical model, free parameters, or postulated entities. Relies on standard assumptions of semiconductor surface chemistry and measurement interpretation.

pith-pipeline@v0.9.0 · 5690 in / 1081 out tokens · 40037 ms · 2026-05-10T18:40:39.011674+00:00 · methodology

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Reference graph

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