Stimulated N-doping of reduced graphene oxide on GaN under excimer laser reduction process Beo Deul Ryu a , Nam Han a , Min Han a , S. Chandramohan a , Young Jae Park a , Kang Bok Ko a , Jong Bae Park b , Tran Viet Cuong a,c , Chang-Hee Hong a,n a School of Semiconductor and Chemical Engineering, Chonbuk National University, Jeon-ju 561-756, Korea b Korea Basic Science Institute (KBSI), Jeonju Center, 664-14 Dukjin dong 1-ga, Dukjin-gu, Jeonju 561-756, South Korea c Department of Solid State Physics, Ho Chi Minh National University, College of Natural Sciences, 227 Nguyen Van Cu Street, District 5, Ho Chi Minh City, Viet nam article info Article history: Received 11 October 2013 Accepted 17 November 2013 Available online 23 November 2013 Keywords: Graphene oxide GaN Laser reduction N-doping abstract Graphene oxide coated on GaN was simultaneously reduced and doped with nitrogen via excimer laser irradiation. Nitrogen dopant was originated from the GaN during the laser-induced dissociation at high energies. This phenomenon was confirmed by the absence of C–N bond formation in laser irradiated graphene oxide on SiO 2 . A top-gated field-effect transistor based on laser reduction of graphene oxide channel on GaN showed n-type behavior via the gate voltage modulation. The present findings indicate a paradigm for the formation of graphene-nitride semiconductor interfaces. & 2013 Elsevier B.V. All rights reserved. 1. Introduction Reduced graphene oxide (rGO) which is derivative of graphene materials has many advantages over graphene produced by high temperature processes, such as a low-cost, scalable, transfer-free process. In particular, its properties can be tailored by modification of C/O ratio, aromatic sizes, and functionalized with nitrogen, fluorine, metal, metal oxide and polymer [1–3]. In fact, graphene oxide (GO) can be reduced by removing of the oxygen-functional groups using chemical, thermal, or photo-reduction methods. Among them, photo-reduction method using KrF laser, ɤ-ray and UV is referred to be fast and low temperature processes as compared to others [4]. An attempt to dope rGO with nitrogen, various nitrogen precursors have been used during high tempera- ture reduction processes such as NH 3 , melamine, and cyanamine to produce rGO with n-type doping. In this context, we introduce a facile method to simultaneously reduce and dope GO with nitrogen using KrF excimer laser. The GO sheets were coated on GaN epitaxial layer and subsequently irra- diated with laser pulses of different energies. Produced nitrogen atom by the laser decomposition of GaN were incorporated into GO. Herein, our main focus is to lowering reduction temperature and nitrogen-free precursor, which may tailor the final material properties. In addition, the role of GaN epitaxial layer and laser power behavior in forming n-doping rGO are also within focus of this work. 2. Experimental GaN epitaxial layer was grown on a c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition (MOCVD). A synthesized GO aqueous solution by a modified Hummers method was sprayed on GaN epilayer. Then, GO was reduced by the KrF excimer laser with different laser energies. The surface morphology and microstructure of rGO were investigated by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD) and Atomic force microscopy (AFM), respectively. For electrical study, transfer length measurement (TLM) contact structures and field effect transistor (FET) devices based on rGO active layer were fabricated and characterized using an Agilent parameter analyzer with four probes station. 3. Results and discussion The high-resolution C1s spectra of as-deposited and pulsed laser irradiated GO films are considered for the evaluation of bonding characteristics in GO films. Fig. 1(a) shows the XPS C1s spectra of the GO films subjected to reduction at different laser energies. The deconvoluted peaks located at the binding energy of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.11.072 n Corresponding author. Tel.: þ82 10 2384 0397; fax: þ82 63 270 3585. E-mail address: chhong@chonbuk.ac.kr (C.-H. Hong). Materials Letters 116 (2014) 412–415