IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 49, NO. 7, JULY 2013 589 Graphene-Si Schottky IR Detector Mina Amirmazlaghani, Farshid Raissi, Omid Habibpour, Josip Vukusic, and Jan Stake, Senior Member, IEEE Abstract—This paper reports on photodetection properties of the graphene-Si schottky junction by measuring current–voltage characteristics under 1.55-μm excitation laser. The measure- ments have been done on a junction fabricated by depositing mechanically exfoliated natural graphite on top of the pre- patterned silicon substrate. The electrical Schottky barrier height is estimated to be (0.44–0.47) eV with a minimum responsivity of 2.8 mA/W corresponding to an internal quantum efficiency of 10%, which is almost an order of magnitude larger than regular Schottky junctions. A possible explanation for the large quantum efficiency related to the 2-D nature of graphene is discussed. Large quantum efficiency, room temperature IR detection, ease of fabrication along with compatibility with Si devices can open a doorway for novel graphene-based photodetectors. Index Terms—Graphene, Si, Schottky diode, Detector. I. I NTRODUCTION G RAPHENE is a two-dimensional material which has attracted much attention due to its remarkable optical, thermal and electronic properties since its discovery in 2004 [1]–[3]. This single atom layer can absorb the incident light in a broadband range of frequencies through interband and intraband transitions [4], [5]. Based on these two transi- tions, in addition to the photo-thermoelectric effect in graphene [6]–[9], different kinds of detectors have been fabricated working at different wavelength ranges [5], [10]–[19]. Among these different frequency ranges of detectors, photo detection properties in the wavelength range from C band (1528–1561 nm) to L band (1561–1620 nm) are of great interest and importance from optical communication point of view [20]. Graphene-FET detectors have been reported to operate at 1.55μm laser illumination with a photo responsivity of 0.5mA/W at a gate bias of 80 V and internal quantum efficiency of (6 to 16)% [11]. This responsivity has been improved to (1.5 to 6.1) mA/W at 15 V gate bias in [12], by creating a wider photo-detection region and providing higher E-field using finger-shaped gates and an asymmetric metallization scheme. However, the responsivities of these photo detectors are restricted by the limited optical absorption Manuscript received December 5, 2012; revised February 26, 2013 and April 10, 2013; accepted April 18, 2013. Date of publication May 3, 2013; date of current version May 31, 2013. M. Amirmazlaghani and F. Raissi are with the Department of Electrical Engineering, K. N. Toosi University of Technology, Tehran 16314, Iran (email: mazlaghani@ee.kntu.ac.ir; raissi@kntu.ac.ir). O. Habibpour, J. Vukusic, and J. Stake are with the Depart- ment of Microtechnology and Nanoscience, Terahertz and Millimetre Wave Laboratory, Chalmers University of Technology, Göteborg 412 96, Sweden (e-mail: omid.habibpour@chalmers.se; josip.vukusic@chalmers.se; jan.stake@chalmers.se). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JQE.2013.2261472 in graphene, short carrier lifetime and small effective photode- tection area [11]–[13]. Different methods have been applied to compensate the limited optical absorption in graphene and recently complete optical absorption in graphene is reported in [21]. Nevertheless, the effects of short carrier life time and small effective photodetection area in graphene detectors have not been solved yet. In order to detect radiation intended for optical communi- cation in Si-based chips, other IR detectors like Germanuim- based photo detectors, all-Si photodetectors and Schottky detectors are usually used [20], [22]–[31]. Germanuim-based photo detector in these wavelength range; which is one of the best choices, is not compatible with Si chips due to the thermal mismatch and their aggressive substrate cleaning processes [23], [24]. All-Si photodetectors, in the best case, have a responsivity peak of 0.08mA/W at 1.55μm [20] while Schottky IR detectors have a limited efficiency (<1%) in most of the cases due to the Fowler theory [26]–[31]. So, exploiting the advantages of a new Si-compatible material like graphene as a more efficient detector alternative is important. The object of this paper is to introduce the graphene-Si Schottky junction as a more sensitive Si compatible IR detector. In this way we can also alleviate the limitations of other graphene-based detectors, such as small effective photodetection area and short carrier life time [11]–[13]. Fabricating a Schottky diode based on graphene has been reported in [32]–[34] previously, although it has not been used as detector. In [32]–[34], graphene is used as a transpar- ent electrode through which visible electromagnetic radiation passes and is absorbed by Si. This photocurrent is generated by electron-hole pairs created inside the substrate near to graphene, where space charge region exists. So, it should be mentioned that graphene is used as a transparent electrode and does not contribute to photocurrent generation in these experiments [32]–[34]. Here, we present a graphene-Si schottky diode as the IR detector under 1.55μm illumination. In particular, we demonstrate the photocurrent generation in graphene taking advantage of especial properties of graphene-Si Schottky diode junctions. Experimental results and theoretical justi- fication are described. The responsivity is in the range of (2.8 to 9.9) mA/W. Considering 2.3% optical absorption in graphene, internal quantum efficiency of (10 to 30)% is achieved. These detectors do not suffer from a short lifetime of graphene carriers due to their fast collecting behavior. Graphene-Si Schottky detectors also provide a larger effective photo detection area, in which the effective photo detection area is limited only by the graphene size. Fast collecting behavior combined with a large photo detection area can improve the previous limitations of Graphene-FETs (GFET) 0018-9197/$31.00 © 2013 IEEE