Bulk photovoltaic effect in hexagonal ${\mathrm{LuMnO}}_{3}$ single crystals

Bulk photovoltaic effect in hexagonal ${LuMnO}_{3}$ single crystals

Yunwei Sheng, Ignasi Fina, Marin Gospodinov, Aaron M. Schankler, Andrew M. Rappe, and Josep Fontcuberta

Phys. Rev. B 104, 184116 – Published 29 November 2021

Abstract

Hexagonal manganites, such as $h − {LuMnO}_{3}$ , are ferroelectric and have a narrow electronic band gap of $\approx 1.5 eV$ . Here we report on the photoresponse of $h − {LuMnO}_{3}$ single crystals. It is found that the short circuit photocurrent density ( $J_{sc}$ ) and the open circuit voltage ( $V_{oc}$ ) are dependent on the direction of the polarization plane of a linearly polarized impinging light. Its angular dependence indicates the contribution of bulk photovoltaic effect to the short circuit photocurrent. It is also observed that a switchable drift photocurrent, originating from the depoling field of the ferroelectric and thus tunable $(< 10 %)$ by its polarization direction, also contributes to $J_{sc}$ . Although its presence precludes accurate determination of the bulk photovoltaic tensor elements and Glass coefficients, some bounds can be established. The Glass coefficients are found to be significantly larger than those obtained in ${BiFeO}_{3}$ . We argue that the smaller band gap of $h − {LuMnO}_{3}$ , its distinctive bipyramidal crystal field, and electronic configuration ( $3 d^{4}$ vs $3 d^{5}$ ), account for the difference and suggest a path towards ferroelectrics of higher photoconversion efficiency.

Received 12 August 2021
Revised 25 October 2021
Accepted 3 November 2021

DOI:https://doi.org/10.1103/PhysRevB.104.184116

Physics Subject Headings (PhySH)

Ferroelectricity Ferroelectrics Photogalvanic effect Photovoltaic absorbers Photovoltaic effect

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Yunwei Sheng ¹, Ignasi Fina ^1,*, Marin Gospodinov², Aaron M. Schankler ³, Andrew M. Rappe ³, and Josep Fontcuberta ^1,†

¹Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra 08193, Catalonia, Spain
²Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
³Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA

^*ifina@icmab.es
^†fontcuberta@icmab.cat

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Vol. 104, Iss. 18 — 1 November 2021

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Figure 1
(a) Photoresponse measurements under illumination of linearly polarized light at incidence angles $θ \approx 0^{\circ} - 60^{\circ}$ . (b) Definition of the light linearly polarized angle φ (angle between $E_{1}$ and $E_{n}$ ), where the dashed ellipse indicates the rotation plane of the polarization vector, and the coordinate system is given by $x y z$ with the $z$ axis along the polar $c$ axis of LMO. The blue arrows denote light propagation of wave vector $k$ . Red arrows denote the light polarization at $φ = 0^{\circ}$ ( $E_{1}$ , parallel with the incidence plane). Purple arrow represents the light polarization at intermediate angle ( $E_{n}$ ).
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Figure 2
Dependence of (a) short circuit current [ $J_{sc} (θ, φ)$ ] and (b) the open circuit voltage [ $V_{oc} (θ, φ)$ ], respectively, on the polarization angles (φ) of the light at different incidence angles, of Cry-1. Solid lines are fits using Eq. (1) of experimental data (symbols). Light intensity $I_{0}$ after optical plates and the top Pt is around $15 W / c m^{2}$ . The sketch illustrates the experimental arrangement. Notice that the illumination is through the top electrode.
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Figure 3
Dependence of the (a) short circuit photocurrent recorded at $φ = 0$ and (b) amplitude $A_{z} (θ)$ on ${sin}^{2} (θ)$ , of Cry-1. Solid lines are linear fits of experimental data (symbols) as indicated. Error bars in figures indicate the spread of values (standard deviation, SD) from data recorded in six pads. Light intensity $I_{0}$ after optical plates and the top Pt is around $15 W / c m^{2}$ .
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Figure 4
$J_{sc} (φ)$ at $θ \approx 45^{\circ}$ incidence (Cry-1) recorded at (a) 405 nm and (b) 638 nm, respectively. Solid lines are fits using Eq. (1) of experimental data (symbols). (c) Dependence of the amplitude $A_{z}$ of the oscillations $J_{sc} (φ)$ as a function of photon energy. Error bars in figures indicate the SD from data recorded in four junctions. Light intensity $I_{0}$ after optical plates and the top Pt is around $0.6 W / c m^{2}$ . Note that absolute values of $J_{sc}$ and $A_{z}$ in (a)–(c) are smaller than in Fig. 2, due to the different laser fluency used in both cases (0.6 and $15 W / c m^{2}$ , respectively). Inset in (c) is adapted from Ref. [29].
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Figure 5
(a) Left axis: $J_{sc} (φ)$ (solid circles) measured at $θ \approx 90^{\circ}$ incidence using a top electrodes of area $S_{1} \times S_{2} = 450 μ m \times 270 μ m = A_{1} \approx 0.12 m m^{2}$ (Cry-2) and $S_{1} \times S_{2} = 770 μ m \times 480 μ m = A_{2} \approx 0.37 m m^{2}$ (Cry-3), placed up to the edge of the crystal surface. Right axis: $I_{sc} (φ) = J_{sc} (φ) \times A$ (solid stars). Light intensity $I_{0}$ after optical plates is around $27.6 W / c m^{2}$ . (b) Sketch of the experimental arrangement. The attenuation length of the light and the contact size $(S_{1}, S_{2})$ are indicated. In the sketch, the edge-electrode distance $(D = 0)$ is not shown.
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Figure 6
Dependence of short circuit photocurrent $J_{sc} (θ, φ)$ on the polarization of light (φ), at various incidence angles (θ), of Cry-1 at prepolarized to $P$ -down and $P$ -up states using $({V_{w}}^{+} / {V_{w}}^{-} = \pm 150 V)$ . Signs “+” and “−” signify positive and negative prepolarizing voltage. Solid lines are fits using Eq. (1) to experimental data (symbols). Light intensity $I_{0}$ after optical plates and the top Pt is around $22.5 W / c m^{2}$ . Data for $J_{sc} (θ \neq 0^{\circ}, φ)$ have been vertically shifted such as $J_{sc} (θ \neq 0^{\circ}, φ = 90^{\circ})$ to coincide with $J_{sc} (θ \neq 0^{\circ}, φ = 90^{\circ}; {V_{w}}^{+} = + 150 V)$ .
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Physical Review B

covering condensed matter and materials physics

Bulk photovoltaic effect in hexagonal ${LuMnO}_{3}$ single crystals

Yunwei Sheng, Ignasi Fina, Marin Gospodinov, Aaron M. Schankler, Andrew M. Rappe, and Josep Fontcuberta

Phys. Rev. B 104, 184116 – Published 29 November 2021

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Physical Review B

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Bulk photovoltaic effect in hexagonal LuMnO3 single crystals

Yunwei Sheng, Ignasi Fina, Marin Gospodinov, Aaron M. Schankler, Andrew M. Rappe, and Josep Fontcuberta

Phys. Rev. B 104, 184116 – Published 29 November 2021

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Bulk photovoltaic effect in hexagonal ${LuMnO}_{3}$ single crystals