Plasmon-enhanced graphene photodetector with CMOS-compatible titanium nitride

Abstract

Graphene has emerged as an ultrafast optoelectronic material for on-chip photodetector applications. The 2D nature of graphene enables its facile integration with complementary metal–oxide semiconductor (CMOS) microelectronics and silicon photonics, yet graphene absorbs only ∼ 2.3 % of light. Plasmonic metals can enhance the responsivity of graphene photodetectors, but may result in CMOS-incompatible devices, depending on the choice of metal. Here we propose a plasmon-enhanced photothermoelectric graphene detector using CMOS-compatible titanium nitride on the silicon-on-insulator platform. The device performance is quantified by its responsivity, operation speed, and noise equivalent power. Its bandwidth exceeds 100 GHz, and it exhibits a nearly flat photoresponse across the telecom C-band. The photodetector responsivity is as high as 1.4 A/W (1.1 A/W external) at an ultra-compact length of 3.5 µm, which is the most compact footprint reported for a graphene-based waveguide photodetector. Furthermore, it operates at zero-bias, consumes zero energy, and has an ultra-low intrinsic noise equivalent power ( N E P &lt;<!-- 20 p W / H z ).

Plasmonic Photovoltaic Double-Graphene Detector Integrated Into TiN Slot Waveguides

“…In practice, Φ B is experimentally extracted as described in [38] because the Schottky-Mott rule does not account for the presence of charged impurities at the metal-semiconductor interface. Even so, a similar conclusion can be reached because of the symmetric doping profile induced by the TiN-Gr-TiN configuration [20].…”

“…The refractive index data of TiN are taken from [20], [24], [45]. Optical simulations were conducted using Lumerical MODE and Lumerical FDTD, where graphene is modeled as a 2D material with a surface optical conductivity (σ) given by [46], [47]:…”

“…Hence, the net photocurrent due to the built-in electric fields is zero. The schottky barrier height (Φ B ) is approximated using the Schottky-Mott rule, as described in [20], [38], [39]. The work function values of graphene and TiN are taken as 4.6 eV [40], [41] and 4.3 eV [42], respectively.…”

“…Most photodetectors employed in SiPh are based on Germanium (Ge) [3], which have been demonstrated with a responsivity exceeding 1 A/W [18]. Moreover, the aforementioned plasmon-enhanced graphene photodetectors employ gold (Au) as the plasmonic material, which in spite of its extraordinary plasmonic properties, it is not a CMOS-compatible metal [19], [20]. Therefore, it is essential to explore alternative device structures to further improve the photoresponse and the compatibility of plasmon-enhanced graphene photodetectors with standard industrial platforms.…”

“…The use of two graphene monolayers boosts the photoresponse of the detector while maintaining an ultra-high bandwidth. TiN is a refractory metal nitride that has optical properties that are similar to Au [21], an electrical conductivity higher than Titanium (Ti) [22], but unlike Au, TiN is CMOS-compatible [20], [23]- [25]. A strong plasmonic enhancement of the optical mode has been reported for photodetectors that are based on plasmonic slot waveguides [5], [11], [13], [26], including the aforementioned graphene photodetector with a record-high responsivity of 0.67 A/W.…”