Photo-Induced Carrier Density, Optical Conductance and Transmittance in Graphene in the Presence of Optic-Phonon Scattering

Abstract

Since the experimental discovery of graphene in 2004 (Novoselov et al., 2004), the investigation of graphene-based electronics and optoelectronics has quickly become one of the most important research topics in condensed matter physics, nano-material science and nano-electronics (Zhang et al., 2005; Berger et al., 2006). Due to its excellent electronic transport, optical, and optoelectronic properties, such as high carrier density (up to 1013 cm−2) and high carrier mobility at room temperature (up to 20 m2/Vs) along with the high optical transmittance in the air-graphene-wafer systems, graphene has been proposed as an advanced material for new generation of electronic and optoelectronic devices. Graphene-based electronic devices exhibit high carrier mobility and quasi ballistic transport over sub-micron scales even at room temperature (Novoselov et al., 2005). It has already been used to realize high-speed and high-frequency electronic devices such as field-effect transistors (Castro et al., 2007), p-n junctions (Gonzalez & Perfetto, 2008), high-frequency devices (Lin et al., 2009), to mention but a few. Very recently, graphene has also been proposed as an advanced transparent conducting material by utilizing its combined excellent transport and optical properties (Eda et al., 2008). It has been shown that graphene can be used to replace conventional indium tin oxide (ITO) transparent electrodes for making better and cheaper optical displays such the LCDs and LEDs (Hogan, 2008). Presently, graphene-based transparent electronics is a hot field of research for both fundamental studies and device applications (Eda et al., 2008). For the usage of graphene as optoelectronic and transparent electronic devices, the investigation of its optical and optoelectronic properties is critical and essential. Recent experimental and theoretical work has demonstrated and predicted some particular and interesting optoelectronic properties in the infrared-to-visible spectral range for air-graphene-wafer systems. In particular, the results obtained from optical transmission (Kuzmenko et al., 2008) and infrared absorption (Li et al., 2008) measurements show the following features. (i) The optical conductance per graphene layer is a universal value σ0 = e2/(4h) in the visible frequency range (Kuzmenko et al., 2008; Li et al., 2008), which can be viewed as an intrinsic property of two-dimensional massless fermions. (ii) The corresponding light transmittance of monolayer and bilayer graphene on SiO2 or Si wafers are, respectively, Photo-Induced Carrier Density, Optical Conductance and Transmittance in Graphene in the Presence of Optic-Phonon Scattering 24