Spectral responsivity and photoconductive gain in thin film black phosphorus photodetectors

Adrien Rousseau; Anne-Laurence Phaneuf-L'Heureux; Elad Eizner; Junjia Wang; L\'eonard Schue; S\'ebastien Francoeur; St\'ephane K\'ena-Cohen

arxiv: 1906.10676 · v1 · pith:B4OZLXPRnew · submitted 2019-06-25 · ⚛️ physics.app-ph

Spectral responsivity and photoconductive gain in thin film black phosphorus photodetectors

Junjia Wang , Adrien Rousseau , Elad Eizner , Anne-Laurence Phaneuf-L'Heureux , L\'eonard Schue , S\'ebastien Francoeur , St\'ephane K\'ena-Cohen This is my paper

Pith reviewed 2026-05-25 15:40 UTC · model grok-4.3

classification ⚛️ physics.app-ph

keywords black phosphorusphotodetectorsspectral responsivityphotoconductive gainpolarization anisotropysurface oxidethin film

0 comments

The pith

Thin film black phosphorus photodetectors reach intrinsic responsivity above 7 A/W in the visible with polarization anisotropy up to 103.

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

The paper measures full spectral responsivity of black phosphorus photodetectors fabricated in the bulk thin film limit and encapsulated for stability. It shows that visible wavelengths produce responsivity exceeding 7 A/W through internal photoconductive gain that varies with gate voltage, while infrared responsivity stays nearly constant with voltage and intensity. Polarization anisotropy between armchair and zigzag directions reaches 103 and holds from the band edge to 500 nm. The authors attribute the visible-infrared contrast to surface oxide contribution. A reader would care because the findings identify concrete wavelength-dependent mechanisms that could guide selective detector design in a single material.

Core claim

Black phosphorus photodetectors in the bulk thin film limit exhibit broadband responsivity from below 400 nm to the 3.8 μm bandgap. In the visible an intrinsic responsivity exceeding 7 A/W arises from internal gain mechanisms. The polarization anisotropy along armchair and zigzag directions reaches 103 and extends from the band edge to 500 nm. Visible responsivity exhibits large photoconductive gain and gate-voltage dependence while infrared responsivity remains nearly independent of gate voltage and incident light intensity under most conditions, attributed to a contribution from the surface oxide. Devices fabricated in inert atmosphere and encapsulated by Al2O3 provide stable operation for

What carries the argument

The contrast between visible photoconductive gain with gate dependence and infrared response independence attributed to surface oxide, together with the crystal-axis polarization anisotropy in responsivity.

If this is right

Visible responsivity above 7 A/W with gate tunability supports high-sensitivity detection in that range.
Polarization anisotropy of 103 enables polarization-selective detection from the band edge to 500 nm.
Infrared response stability against voltage and intensity variations follows from the surface oxide contribution.
Inert fabrication plus Al2O3 encapsulation yields devices stable beyond six months.
Broadband coverage from ultraviolet to 3.8 μm is achieved within one material system.

Where Pith is reading between the lines

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

Varying oxide thickness during fabrication could be used to adjust the balance between visible gain and infrared stability.
The anisotropy range suggests possible use in polarization imaging or sensing applications that require contrast down to 500 nm.
If surface oxide dominates the infrared behavior, removing or passivating it might make infrared response also show photoconductive gain.
Similar layered materials could be screened for comparable visible-infrared response splits driven by surface layers.

Load-bearing premise

The infrared responsivity independence stems from surface oxide contribution rather than trap states, contact effects, or other mechanisms.

What would settle it

Measurements on otherwise identical devices fabricated without surface oxide that show infrared responsivity becoming dependent on gate voltage or light intensity would challenge the attribution.

read the original abstract

We have fabricated black phosphorus photodetectors and characterized their full spectral responsivity. These devices, which are effectively in the bulk thin film limit, show broadband responsivity ranging from <400 nm to the ~3.8 $\mu$m bandgap. In the visible, an intrinsic responsivity >7 A/W can be obtained due to internal gain mechanisms. By examining the full spectral response, we identify a sharp contrast between the visible and infrared behavior. In particular, the visible responsivity shows a large photoconductive gain and gate-voltge dependence, while the infrared responsivity is nearly independent of gate voltage and incident light intensity under most conditions. This is attributed to a contribution from the surface oxide. In addition, we find that the polarization anisotropy in responsivity along armchair and zigzag directions can be as large as 103 and extends from the band edge to 500 nm. The devices were fabricated in an inert atmosphere and encapsulated by Al$_2$O$_3$ providing stable operation for more than 6 months.

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 measured responsivity numbers and anisotropy data for encapsulated black phosphorus photodetectors, but the surface oxide attribution for the IR behavior lacks explicit controls.

read the letter

The main things to know are that this work reports concrete experimental values for spectral responsivity in thin-film black phosphorus devices, including intrinsic responsivity above 7 A/W in the visible from gain, broadband coverage to 3.8 μm, and polarization anisotropy reaching 103 along the armchair and zigzag axes that holds from the band edge to 500 nm. Those are the usable outputs for device work in this subfield. The devices are encapsulated with Al2O3 after inert-atmosphere fabrication and show stability over six months, which is a practical detail worth noting. The paper also draws a clear contrast between the gate- and intensity-dependent visible response and the more stable infrared response, attributing the latter to surface oxide contribution. The measurements themselves look internally consistent with no circular derivations or free parameters. The full spectral scan and quantified anisotropy add specific numbers that extend prior reports on the material. The soft spot is the oxide attribution. The description states the link directly from the observed visible/IR difference but does not describe oxide thickness or composition checks, control samples without oxide, or other tests that would separate it from bulk traps or contact effects. That part of the interpretation therefore rests on the contrast alone. This is a characterization paper aimed at readers who need reference performance metrics for 2D photodetectors. A device engineer comparing gain or anisotropy values would get something concrete from it. I would send it for peer review. The experimental claims are worth a referee's time to check the data quality and whether the controls back the oxide claim.

Referee Report

2 major / 3 minor

Summary. The manuscript reports fabrication of black phosphorus photodetectors in the bulk thin-film limit with Al2O3 encapsulation, demonstrating broadband spectral responsivity from <400 nm to the ~3.8 μm bandgap. Key findings include intrinsic responsivity >7 A/W in the visible due to photoconductive gain, polarization anisotropy in responsivity reaching 10^3 along armchair/zigzag directions extending from the band edge to 500 nm, and a sharp visible/IR contrast: visible responsivity exhibits large gain and gate-voltage dependence while IR responsivity is nearly independent of gate voltage and intensity, attributed to surface oxide contribution. Devices show stable operation for >6 months.

Significance. If the surface-oxide attribution for the IR behavior is substantiated, the work provides useful experimental data on spectral selectivity and anisotropy in BP photodetectors, potentially informing device engineering for broadband or polarization-sensitive applications. The reported anisotropy value and visible gain are notable experimental observations.

major comments (2)

[Abstract / spectral responsivity results] Abstract and results section on spectral contrast: the central claim of a sharp visible/IR behavioral difference (visible showing photoconductive gain and gate dependence; IR independent of voltage and intensity) is attributed to surface oxide, but no explicit controls (e.g., oxide thickness/composition measurements, oxide-free reference devices, or trap-state characterization) are described to distinguish this from bulk traps or contact effects; this attribution is load-bearing for interpreting the contrast as oxide-specific rather than generic.
[Device fabrication and characterization] Device characterization section: the statement that devices are 'effectively in the bulk thin film limit' is used to support the oxide attribution, yet no supporting data (e.g., thickness-dependent measurements or comparison to thinner flakes) are referenced to confirm this limit and rule out thickness-related trap contributions to the IR independence.

minor comments (3)

[Abstract] Abstract: typo 'gate-voltge' should be 'gate-voltage'.
[Abstract] Abstract: '103' should be written as '10^3' or '1000' for clarity on the anisotropy magnitude.
[Figures and methods] Figure captions and methods: ensure error bars, number of devices measured, and statistics are explicitly stated for all responsivity and anisotropy values to allow assessment of reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for highlighting these points regarding the interpretation of our results. We address each major comment below.

read point-by-point responses

Referee: [Abstract / spectral responsivity results] Abstract and results section on spectral contrast: the central claim of a sharp visible/IR behavioral difference (visible showing photoconductive gain and gate dependence; IR independent of voltage and intensity) is attributed to surface oxide, but no explicit controls (e.g., oxide thickness/composition measurements, oxide-free reference devices, or trap-state characterization) are described to distinguish this from bulk traps or contact effects; this attribution is load-bearing for interpreting the contrast as oxide-specific rather than generic.

Authors: The attribution to surface oxide is presented as an interpretation supported by the stark contrast in gate-voltage and intensity dependence between the visible and IR regimes, which is consistent with prior reports on BP surface oxidation. We agree that direct controls (oxide thickness measurements, oxide-free references, or trap spectroscopy) are not included and would strengthen the claim. We will revise the relevant sections to explicitly frame the oxide contribution as an interpretation based on the observed behavioral contrast rather than a conclusively demonstrated mechanism, and we will note the absence of such controls as a limitation. revision: yes
Referee: [Device fabrication and characterization] Device characterization section: the statement that devices are 'effectively in the bulk thin film limit' is used to support the oxide attribution, yet no supporting data (e.g., thickness-dependent measurements or comparison to thinner flakes) are referenced to confirm this limit and rule out thickness-related trap contributions to the IR independence.

Authors: The devices studied have thicknesses (typically 50–200 nm) for which BP exhibits bulk-like electronic properties, but the manuscript does not include explicit thickness-dependent measurements or direct comparisons to thinner flakes. We will revise the device characterization section to specify the thickness range used, provide the rationale for the bulk-limit description, and acknowledge that thickness-dependent data would help rule out thickness-related contributions to the observed IR behavior. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental device characterization

full rationale

The paper reports fabrication of black phosphorus photodetectors in inert atmosphere, Al2O3 encapsulation, and direct spectral responsivity measurements from <400 nm to ~3.8 μm. Claims of intrinsic responsivity >7 A/W, polarization anisotropy up to 103, visible photoconductive gain with gate dependence, and IR independence attributed to surface oxide are all grounded in empirical observations and device behavior, with no equations, fitted parameters, derivations, or self-citations that reduce to self-referential inputs. The attribution of IR behavior is presented as an interpretation of measured contrasts rather than a derived result. No load-bearing steps match any enumerated circularity pattern.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental fabrication and optical characterization paper; no mathematical model, free parameters, or postulated entities are introduced.

pith-pipeline@v0.9.0 · 5749 in / 1138 out tokens · 17753 ms · 2026-05-25T15:40:57.287399+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

[1]

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Qiao, J.; Kong, X.; Hu, Z.-X.; Yang, F.; Ji, W., High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus. Nature Communications 2014, 5, 4475. 14. Du, Y.; Liu, H.; Deng, Y.; Ye, P. D., Device Perspective for Black Phosphorus Field-Effect Transistors: Contact Resistance, Ambipolar Behavior, and Scaling. ACS Nano 2014, 8 (10), ...

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Huang, M.; Wang, M.; Chen, C.; Ma, Z.; Li, X.; Han, J.; Wu, Y., Broadband Black-Phosphorus Photodetectors with High Responsivity. Advanced Materials 2016, 28 (18), 3481-3485. 31. Ye, L.; Li, H.; Chen, Z.; Xu, J., Near-Infrared Photodetector Based on MoS2/Black Phosphorus Heterojunction. ACS Photonics 2016, 3 (4), 692-699. 32. Bullock, J.; Amani, M.; Cho, ...

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[1] [1]

Nature Communications 2014, 5, 4475

Qiao, J.; Kong, X.; Hu, Z.-X.; Yang, F.; Ji, W., High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus. Nature Communications 2014, 5, 4475. 14. Du, Y.; Liu, H.; Deng, Y.; Ye, P. D., Device Perspective for Black Phosphorus Field-Effect Transistors: Contact Resistance, Ambipolar Behavior, and Scaling. ACS Nano 2014, 8 (10), ...

work page 2014

[2] [2]

Advanced Materials 2016, 28 (18), 3481-3485

Huang, M.; Wang, M.; Chen, C.; Ma, Z.; Li, X.; Han, J.; Wu, Y., Broadband Black-Phosphorus Photodetectors with High Responsivity. Advanced Materials 2016, 28 (18), 3481-3485. 31. Ye, L.; Li, H.; Chen, Z.; Xu, J., Near-Infrared Photodetector Based on MoS2/Black Phosphorus Heterojunction. ACS Photonics 2016, 3 (4), 692-699. 32. Bullock, J.; Amani, M.; Cho, ...

work page 2016