High Responsivity, Broadband, and Fast Graphene/Silicon Photodetector in Photoconductor Mode

Abstract

COMMUNICATIONIn this paper, we present a highly broadband (from visible to infrared) photodetector based on chemical vapor deposition (CVD) graphene-silicon heterostructure, together to be operated in photoconductor mode. This device shows very high responsivity (>10 4 A W −1 ) at wavelength of 632 nm, where light absorption relies on silicon. More importantly, even in the infrared region (1550 nm), where light absorption only depends on the graphene, the responsivity of our detector can be as high as 0.23 A W −1 , which is much higher those by pure monolayer graphene-based devices without optically assisted structure in this spectral region. [ 13,15,24 ] The signifi cant response is mainly due to the fact that the built-in fi eld in heterostructure can effectively prolong the ultrashort lifetime of photon-induced carriers. Besides, we also fi nd three dynamic processes in the transient response: photo-induced carriers sweeping into graphene by the built-in fi eld, electrons in the depletion region diffusion back to graphene, and photo-induced carriers in the bulk silicon diffusion to graphene. Due to the fi rst mechanism, the response time of our detector is less than 3 µs, which has not been reported among graphene photoconductor/ phototransistors. [ 1 ] The structure of graphene-silicon heterostructural photodetector is schematically shown in Figure 1 a. The start wafer we employed is a lightly doped p-type silicon wafer (>100 Ω). A thin layer of SiO 2 is grown on silicon and patterned a window on top. Then, the CVD graphene (the Raman spectra is shown in Figure S1, Supporting Information) is transferred, and both electrodes are deposited on graphene. The SiO 2 layer can avoid the overlap between the electrode and silicon. A Schottky junction is thus formed at the interface between graphene and silicon. The Fermi level differences are measured by Kelvin probe force microscopy (KPFM) in the dark. As shown in Figure 1 b, the surface potential differences (approximately similar to the work function misalignment for clean samples) between graphene and silicon, and between graphene and gold are about 0.08 and 0.16 eV, respectively. Under ambient conditions, the work function of gold is around 4.8 to 4.9 eV. [ 25,26 ] By taking the intrinsic work function of graphene (≈4.56 eV) [30][31][32] into consideration, an energy band diagram is depicted in Figure 1 c. The Fermi energy of graphene should be around 0.16 to 0.26 eV. A built-in fi eld forms at the surface, which directs from silicon to graphene. The graphene not only functions as the charge transport channel, but also works as the light absorber for the light with photon energy lower than the Fermi energy.In the visible light experiment, the photodetector is characterized by the laser at wavelength of 625 nm. Optical attenuators are introduced to change the input power. DOI: 10.1002/adom.201500127Graphene is thought to be an ideal material for novel photodetectors due to its unique properties. [1][2][3] For example, its zero bandgap affords the benefi t of ultr...

Silicon-graphene conductive photodetector with ultra-high responsivity

“…As shown in Fig. 2(a), when the input optical power increases, the total current I total decreases, which is different from the results of graphene/P-doped silicon photodetector reported previously17. For graphene/P-doped silicon photodetector demonstrated in ref.…”

“…For graphene/P-doped silicon photodetector demonstrated in ref. 17, the total current I total rises with increasing input optical power and is larger than the dark current I dark . This can be explained from the carrier transport in the Schottky junction formed between the graphene sheet and the silicon substrate.…”

“…Similarly, Chen et al . demonstrated a silicon-graphene conductive photodetector with further improved response time around 3 μs by using a lightly-doped P-type silicon substrate while the responsivity further decreases to ~10 4  A/W under an input optical power of 0.112 μW17.…”

Anomalous temperature coefficient of resistance in graphene nanowalls/polymer films and applications in infrared photodetectors

“…Considering this, researchers focused on exploring effective methods to improve the absorption, for example, plasmon enhancement [10,11], waveguide [12,13], and quantum dots [14,15]. However, the desired absorptivity is limited by the narrowband absorption due to the optical characteristics of those structures [16]. Except for low light absorption, the intrinsic TCR of graphene also shows poor superiority, which is −0.05% K −1 only.…”

“…Except for low light absorption, the intrinsic TCR of graphene also shows poor superiority, which is −0.05% K −1 only. Researchers [15][16][17][18] have done a lot of works for the purpose of enhancing the TCR of graphene in which the maximum value is −4% K −1 accompanied with a complicated fabrication process. Apparently, it is challenging to simultaneously possess both broadband strong absorption and high TCR value for the bolometric sensing materials.…”