Interface control and photovoltaic properties of n-type silicon/metal junction by organic dye F. Yakuphanoglu a,⇑ , Y.S. Ocak b , T. Kılıçog ˘lu c,d , W.A. Farooq e a Metallurgical and Materials Engineering Department, Firat University, Elazig, Turkey b Department of Science, Faculty of Education, Dicle University, Diyarbakır, Turkey c Department of Physics, Faculty of Science, Dicle University, Diyarbakır, Turkey d Department of Physics, Faculty of Arts and Sciences, Batman University, Batman, Turkey e Department of Physics and Astronomy, College of Science, King Saud University, Riyadh, Saudi Arabia article info Article history: Received 2 December 2010 Received in revised form 4 March 2011 Accepted 7 April 2011 Available online 13 April 2011 Keywords: Inorganic–organic diode Organic semiconductors Interface state properties abstract The electronic parameters and photovoltaic properties of the Au/methylene blue/n-Si diodes were inves- tigated by current–voltage and capacitance–conductance–frequency techniques. The diode exhibits a non-ideal behavior due the series resistance, organic layer and oxide layer. The barrier height (1.04 eV) of the Au/methylene blue/n-Si is higher than that of Au/n-Si Schottky diode (0.83 eV) due to an excess barrier formed by organic layer. The interface state density of the diode was determined using a conduc- tance technique and was found to be 3.25  10 12 eV 1 cm 2 . The diode shows a photovoltaic behavior with a maximum open circuit voltage V oc of 0.23 V and short-circuit current I sc of 20.8 lA under 100 mW/cm 2 . It is evaluated that Au/methylene blue/n-Si is an organic-on-inorganic photodiode with the obtained electronic parameters and methylene blue organic dye controls the interface and electrical properties of conventional metal/n-type silicon junction. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction The interest on studies related to organic based electronic and photoelectrical devices has been increased in last several decades, because they may offer some key advantages such as low cost and easy preparation techniques, possibility of synthesis for different purposes and large area coverage. Organic dyes, especially, have been extensively used in electronic and photoelectrical devices including light emitting diodes and solar cells [1] and they have been used in solar cells because of their high thermal and chemical stabilities and high photoconductive properties [1]. Organic–inor- ganic (OI) heterojunctions are one of the classes of electronic and photoelectrical devices. They are widely studied to use the advan- tages of both organic and inorganic materials in a single structure [2–20]. Recently, electrical and photoelectrical characterization of quercetin/p-InP [2], FSS/n-Si [3], p-Si/C 60 :MEH-PPV [5] and BODI- PY/n-Si [9] have been investigated. All the studies have showed that OI heterojunctions can be used as solar cells, photodiodes and optical sensors. Methylene blue (C 16 H 18 N 3 ClS) is a good candidate to obtain OI devices such as solar cells, photodiodes and Schottky diodes. Owing to its conjugated structure, 14p electrons and 4.7 eV work function [21], it has been chosen as an organic material in the formation of the OI structure. It is one of the very common organic dyes used in chemistry, biology and medicine. It is a bright green- ish blue organic dye belonging to the phenothiazine family. It is employed as a chemical oxidation–reduction indicator [22] and a biological stain [23,24]. The aim of the study is obtain the Au/organic dye/n-Si structure and determine the possibility of obtain solar cells with methylene blue interface. For this aim, Au/methylene blue/n-Si structure was fabricated by forming a thin methylene blue layer on n-Si wafer by dip coating technique. The electrical properties of the structure have been determined by current–voltage (I–V) and capacitance– voltage (C–V) and capacitance–frequency (C–f) properties of the device in dark. In addition, the photovoltaic properties of the de- vice have been determined by its I–V measurements under light. 2. Experimental details The organic-on-inorganic (OI) structure was fabricated using one side polished n-Si wafer with (1 0 0) orientation and 1– 10 X cm resistivity. Firstly, the wafer was degreased for 5 min in boiling tricholoroethylene, and then rinsed by ultrasonic vibration in acetone and isopropanol to get rid of organic contaminations. The wafer was etched in HF/H 2 O (1:10) solution to remove native oxide layer on its surface. Preceding each step, n-Si wafer was rinsed in deionized water. After all these cleaning procedures, it was dried under N 2 atmosphere and inserted into a vacuum system 0167-9317/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2011.04.029 ⇑ Corresponding author. Tel.: +90 424 237 00 00x6378; fax: +90 424 238 83 87. E-mail address: fyhanoglu@firat.edu.tr (F. Yakuphanoglu). Microelectronic Engineering 88 (2011) 2951–2954 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee