Enhanced photodetection in graphene-integrated photonic crystal cavity

Abstract

We demonstrate the controlled enhancement of photoresponsivity in a graphene photodetector by coupling to slow light modes in a long photonic crystal linear defect cavity. Near the Brillouin zone (BZ) boundary, spectral coupling of multiple cavity modes results in broad-band photocurrent enhancement from 1530 nm to 1540 nm.Away from the BZ boundary, individual cavity resonances enhance the photocurrent eight-fold in narrow resonant peaks. Optimization of the photocurrent via critical coupling of the incident field with the graphene-cavity system is discussed. The enhanced photocurrent demonstrates the feasibility of a wavelength-scale graphene photodetector for efficient photodetection with high spectral selectivity and broadband response. a) These authors contribute equally to this work 1 arXiv:1311.2080v1 [cond-mat.mes-hall] 8 Nov 2013The unique properties of graphene have generated strong interest in developing optoelectronics devices based on the material 1,2 . Examples include graphene-based high speed electro-optical modulators 3,4 , photodetectors 5,6 , saturable absorbers 7,8 , and nonlinear media for four-wave mixing 9-11 . Intrinsic graphene exhibits absorption of 2.3% 12 in the infrared to visible spectra range. While this absorption coefficient is remarkably high for a single atomic layer, for practical applications, a larger absorption coefficient is needed. To increase the light-matter interactions in graphene, approaches to date have included the integration of graphene with optical micro-cavities 13-17 , plasmonic nanostructures 18-22 and silicon photonic waveguides 3,4,23,24 .In this paper, we demonstrate a graphene photodetector integrated in a linear defect cavity defined in a planar photonic crystal (PPC). A single graphene layer strongly couples to the cavity evanescent field, increasing the light-matter interaction in graphene 25 for photocurrent generation. Coupled mode theory predicts maximal absorption into the graphene absorber when the intrinsic cavity loss rate, κ c , equals the loss rate into the graphene sheet, κ cg 25 .Upon optimization of the cavity design, we obtain nearly critical coupling with κ cg /κ c ≈ 1.3 and observe an eight-fold enhancement of photocurrent in the graphene photo-detector. The observed reflectivity and photocurrent spectra in the graphene detector agree well with the coupled graphene-cavity model. Spatial mapping of the photocurrent allows us to compare the response of the graphene detector with and without optical enhancement via the PPC cavity.The PPC cavity-integrated graphene photodetector is illustrated in Fig. 1(a). An airsuspended PPC cavity was fabricated on a silicon-on-insulator wafer with a 260 nm thick silicon (Si) membrane, using a combination of electron beam lithography (EBL) and dry/wet etching steps. The PPC has a lattice spacing of a = 450 nm and hole radius of 0.29a. A linear defect in the center of the PPC lattice forms a long cavity ( Fig. 1(b)), producing bounded cavity modes. A layer of 20 nm hafnium oxide (HfO 2 ), deposited by atomic...

Nanocavity absorption enhancement for two-dimensional material monolayer systems

“…However, the obtained peak optical absorption is still relatively low, which is 8%~9%. In recent years, different methods were proposed to enhance the optical absorption with impressively high optical absorption records reported theoretically [12][13][14] and experimentally [15,16]. However, for many enhancement mechanisms, 2D material monolayers were usually embedded inside microcavities, resulting in that the enhanced optical absorption cannot be conveniently used in applications like biosensing [17,18] and surface-enhanced photocatalysis [19] where the interaction between the 2D materials and the surrounding environment is needed.…”

Integration of 2D materials on a silicon photonics platform for optoelectronics applications

“…The inability to turn off the conductance of graphene devices leads to continuous energy consumption and high shot noise associated with the dark current, which significantly limit their use in real-world applications. One solution is to operate graphene photodetectors in the photovoltaic mode at zero bias and rely on a built-in asymmetric field profile to sweep photo-excited carriers to the metal contacts [22][23][24][25][26][27][28][29][30][31][32]. However, this approach is limited by the relatively weak responsivity at zero bias.…”

“…To measure the optical absorption in the bottom layer with high precision, the device was placed onto one arm of an unbalanced Mach-Zehnder interferometer. Other designs have used photonic crystal waveguides to guide light [28] and enhance optical absorption through cavity resonance [29]. While this can improve optical absorption and allow for devices with smaller footprints, incorporating resonant enhancement will of course limit the usable optical bandwidth of the device.…”

On-chip graphene optoelectronic devices for high-speed modulation and photodetection

“…To understand the measured spectra, we use the parameters of cavity intrinsic loss κ c , graphene-induced excess loss κ cg and the resonant frequency ω of the cavity modes extracted from the cavity reflection in Fig. 5(b) using the coupled mode theory, 19 and calculate the absorption in graphene as a function of input wavelengths. The purple dashed curve in Fig.…”