Universal reconstructive polarimetry with graphene-metal infrared photodetectors

Abstract

Measurement of light polarization has long been based on complex, bulk, and slow optical instruments. The advent of materials with in-situ variable polarization photoresponse has led to the concept of reconstructive polarimetry, where the detector itself plays the role of tunable polarizer. Materials enabling such functionality have been limited to complex van der Waals heterostructures. Here, we demonstrate the reconstructive polarimetry with infrared (IR) detectors based on simple gated graphene-metal junctions. The reconstruction exploits the gate tuning of polarization contrast, which enables the evaluation of both infrared power and polarization angle from photovoltage measurements at two sequential gate voltages. The physics enabling the polarimetry lies in polarization-dependent shift of the electron hot spot near the contact, and the gate tuning of the of light-sensitive barrier width. We further show the universality of polarization reconstruction, i.e. its feasibility with different geometries of the junction, and with graphene of different quality, from hBN-encapsulated to the scalable vapor-deposited wet-transferred samples.

Figures (4)

• Figure 1: Principle and demonstration of reconstructive polarimetry with gate-controlled graphene detector. The principle of reconstructive polarimetry is based on calibration of device responsivity $R$ vs polarization angle $\theta$ and control gate voltage $V_{\rm g}$. The procedure is shown in panel (a). The reconstruction, shown in (b), is based on readout of photovoltage $V_{\rm ph}$ at two subsequent control voltages $V_{\rm g}^{(1),(2)}$. This is generally sufficient to determine two radiation characteristics: power $P_x$ and polarization angle $\theta_x$. (c) Gate-and polarization-dependent photovoltage for graphene detector with geometrically patterned contacts shown in the inset. Scale bar is 20 $\mu$m. (d) Computed quality of polarization resolution $Q$ as a function of control voltage pair used for reconstruction. Optimal working points are marked by color circles. (e) Polarization-dependent photovoltage of metal-graphene detector showing large variations of polarization contrast with gate voltage. (f,g) Demonstration of polarization reconstruction for operation at selected combinations of gate voltage $V_{\rm g} = \{-5,\,-29\}$ V (f) and $V_{\rm g} = \{8.5,\,29\}$ V (g). Gray circles represent the angles used at the calibration stage (marked as 'Lrn'), orange circles represent the angles subject to computational reconstruction (marked as 'Rcnstr').
• Figure 2: Universality of the reconstructive polarimetry with dissimilar graphene photodetectors. Panels (a-c) show the experimentally measured polarization-dependent photovoltages at different gate voltages for three different detector structures. All devices feature gate-tunable polarization contrast. Micro-photographs of the detectors are shown in panels (g-i): (g) hBN-encapsulated graphene photodetector with different source and drain widths (h) photodetector with non-parallel source and drain contacts and a top gate (i) photodetector with inversion-asymmetric metallic metasurface deposited directly atop graphene. Panels (d-f) show the computed quality of polarization reconstruction for the three respective detectors. Scale bars are 2 $\mu$m (g), 20 $\mu$m (h) and 50 $\mu$m (i).
• Figure 3: Theoretical modeling of polarization-resolving detection at a metal-graphene interface.(a-d) Microscopic distributions of various physical quantities at metal-graphene junctions upon mid-IR illumination. (a) - local absorbance (b) - light-induced change in electron temperature (c) - profile of electron potential energy, the band diagram (d) - profile of local Seebeck coefficient. (e) gate-dependent photovoltage computed with microscopic quantities (a-d) for various angles of linear polarization marked with colors. Inset in (e) shows the polarization ratio defined as ${\rm PR}(\theta) = V_{\rm ph}(\theta)/V_{\rm ph}(\theta=0)$. Dashed lines show the portion of photovoltage generated in the bulk of graphene (f) polarization reconstruction quality $Q$ computed from the photovoltage in (e), $\log_{10}$ scale
• Figure 4: Polarization reconstruction for disconnected metasurface device (Fig. 2 i) with 30 working gate voltages.