Device Model for Graphene Nanoribbon Phototransistor

Abstract

An analytical device model for a graphene nanoribbon phototransistor (GNR-PT) is presented. GNR-PT is based on an array of graphene nanoribbons with the side source and drain contacts, which is sandwiched between the highly conducting substrate and the top gate. Using the developed model, we derive the explicit analytical relationships for the source-drain current as a function of the intensity and frequency of the incident radiation and find the detector responsivity. It is shown that GNR-PTs can be rather effective photodetectors in infrared and terahertz ranges of spectrum.Photodetectors for far infrared (FIR) and terahertz (THz) ranges of spectrum are conventionally made of narrow-gap semiconductors and quantum-well structures. In the former case, interband transitions due to the absorption of photons are used. The operation of the detectors based on quantum-well structures is associated with the electron or hole intraband (intersubband) transitions [1, 2]. Some time ago, quantumdot and quantum-wire detectors were proposed [3,4]. The transition from quantum well structures with twodimensional electron (hole) spectrum to low-dimensional structures such as quantum-wire and quantum-dot structures might lead to a significant improvement of the FIR and THz detectors (see, for instance, ref.[5] and the references therein). The utilization of graphene, i.e., a monolayer of carbon atoms forming a dense honeycomb two-dimensional crystal structure [6,7,8,9, 10] opens up tempting prospects in creation of novel FIR and THz devices [11,12,13,14,15], in particular, novel photodetectors. One of the most promising metamaterials for FIR and THz detectors is a patterned graphene which constitutes an array of graphene nanoribbons (GNRs). The energy gap between the valence and conduction bands in GNRs as well as the intraband subbands can be engineered varying the shape of GNRs, in particular, their width, which can be defined by lithography. [16,17,18]. This opens up the prospects of creation of multicolor photodetectors.In this paper, we propose of a graphene nanoribbon phototransistor (GNR-PT) and evaluate its performance using the developed device model. The detector proposed has a structure of GNR field-effect transistor consisting of an array of GNRs with the side source and drain contacts (to each GNR) sandwiched between the highly conducting substrate and the top gate electrode. The operation of devices with similar structure were explored recently (see, for instance, [17,18,19,20,21,22,23]). Here, we study The structure of GNR-PT under consideration is schematically shown in Fig. 1. For the sake of definiteness, we consider a GNR-PT with optical input from the bottom of the structure assuming that the substrate and the layer sandwiching the GNR array are transparent.Graphene nanoribbons exhibit the energy spectrum with a gap between the valence and conduction bands depending on the nanoribbon width d:

Electrically inducedn−i−pjunctions in multiple graphene layer structures

“…2(c)) is an important characteristic of such junctions [16]. In particular, this current can substantially affect the performance of the terahertz tunneling transit-time oscillators and interband photodetectors [5,13]. This current is associated with the thermogeneration and tunneling generation of the electronhole pairs in the i-region.…”

“…Depending on the n-i-p junction applications, the quantities V and l should be chosen to provide either domination of tunneling current (as in tunneling transit-time oscillators [4]) or its suppression (as in the interband photodetectors [13]). …”

“…Such devices include, in particular, terahertz tunneling transit-time oscillators (similar to that considered in Ref. [4]), lasers with optical and electrical pumping, and high performance interband photodetectors [11][12][13]. Gated multiple-GL structures can be also used in high-frequency field-effect transistors [14] and other devices (the terahertz frequency multipliers, and plasmonic devices).…”

Terahertz and infrared photodetectors based on multiple graphene layer and nanoribbon structures

“…In particular, GLs and MGLs exhibit very specific optical properties associated with the gapless energy spectrum and linear dispersion law for electrons and holes (see, for instance, an extensive review by Castro Neto et al [1]). Owing to a rather high quantum efficiency of interband transitions in a single GL (SGL), graphene na− noribbons (GNRs), and graphene bilayers (GBLs) [1,2], they are very promising for detectors of terahertz (THz) and infrared radiation (IR) [3][4][5][6][7][8]. Indeed, the probability of absorption b, of a photon incident on a GL (at the zero tem− perature) is expressed via the fundamental constants: b = p pa e c 2 0 023 h = @ .…”

“…The emerging of the energy gap promotes a substantial weakening of the inter− band tunnelling and, consequently, lowering of the dark current and enhancement of the detector detectivity. By vir− tue of the energy gap in GNR structures, they can be used not only for photodiodes but also for phototransistors [3].…”