International Journal of Scientific & Engineering Research, Volume 6, Issue 7, July-2015 1664 ISSN 2229-5518 IJSER © 2015 http://www.ijser.org Etching Effect on Sensing Behavior of CuO:NiO/PS Hydrogen Gas Sensor Isam M. Ibrahim 1 , Yahya R. Hathal 1,2 , Fuad T. Ibrahim 1 and Mudhafar H. ALI* 2 Abstract— In this paper, thin films of copper oxide nanoparticles mixed with 2% wt of nickel oxide are deposited on glass and porous silicon (PS) substrates with orientation (111) etched at 30 minutes. The current density was varied from (10 to 50) mA/cm2 with a step of 10 utilizing pulsed laser deposition technique for the manufacture of hydrogen gas sensor. The films are annealed in air at 400 °C for two hours. The PL result of PS shows that the peak position is shifted to the higher wavelength region due to increase etching current. On the other hand, the atomic force microscopy shows an increase in average diameter with increasing etching current (10-30) mA then decrease. Moreover, the FTIR spectra of porous silicon exhibit that the pore surface includes a high density of dangling bonds of Si for original impurities such as hydrogen and fluorine, which are residuals from the electrolyte. Finally the sensitivity of the hydrogen gas sensor are increased with increasing operating temperature. Index Terms— Gas Sensors, Pulsed Laser Deposition, Metal Oxide, Atomic Force Microscope ——————————  —————————— 1 INTRODUCTION Hydrogen gas is tasteless, colorless and odorless so it cannot be detected by human beings. The low ignition energy and wide flammable range makes it easy inflammable and explosive. Therefore rapid and accurate hydrogen detection is necessary during the production, storage and use of hydrogen and it is also essential for monitoring/controlling the hydrogen concentration of nuclear reactors, coal mines and semiconductor manufacturing [1]. Porous silicon (PS) a nanostructured material, has attracted considerable attention as a measure to enhance the optical properties of silicon (Si). The formation of PS layers on crystalline Si (c-Si) wafers using electrochemical etching (ECE) exhibits photo luminescent and electroluminescent properties similar to those of semiconductors with direct energy gap . PS has emerged as an attractive material in the field of electronics and optoelectronics due to its broad band gap, wide optical transmission range (700–1000 nm), wide absorption spectrum, surface roughening and good anti-reflection coating (ARC). The surface roughness and lower effective refractive index, which can reduce the reflection losses of sunlight radiation are the primary factors that enhance PS compared with c-Si[2]. The physical properties of porous silicon are fundamentally determined by the shape, diameter of pores, porosity, and the thickness of the formed porous layer. ———————————————— 1 Department of physics, College of Science, University of Baghdad, Baghdad, Iraq. 2 Rewnable Energy Center, Ministry of Science and Technology, Baghdad, Iraq. * Corresponding Author: muthafarh@yahoo.com Depending on the etching parameters, for example current density, HF concentration, or substrate doping type and level, the physical properties of PS can be varied. In addition, when the feature size of the pores of PS is less than a few nanometers, various quantum-size effects occur, which make PS even more fascinating [3]. Oxide semiconductors been used to detect oxidizing and reducing gases in simple and cost-effective have manner[4]. Their chemiresistive variation emanates from the oxidative or reductive interaction of the analytic gas with the oxide semiconductor surface and the consequent change in the charge carrier concentration. In p-type oxide semiconductor gas sensors such as those comprising CuO, NiO, Co3O4, and Cr2O3, the adsorption of negatively charged oxygen forms a hole accumulation layer near the surface. Thus, conduction occurs along the conductive hole accumulation layer[5]. Copper oxides are semiconductors and have been studied for several reasons such as: the natural abundance of starting material (Cu), the easiness of production by Cu oxidation, their non-toxic nature and the reasonably good electrical and optical properties exhibited by Cu2O. Cupric oxide (CuO) is a p-type semiconductor having a band gap of 1.21–1.51 eV and monoclinic crystal structure [6]. Copper oxides are used for gas sensors for hydrogen, volatile organic compounds catalysis and specially cuprous oxide films were intensively researched in device applications such as photovoltaic solar cell, photo electrochemical cell and electrochromic coatings [7] Nickel oxide (NiO) is p-type semiconductor material and is widely used in different applications such as transparent conductive films and electrochromic devices, as a potential candidate in the chemical sensors. NiO exhibits a wide band gap of 3.6–4.0 eV at room temperature; thus, NiO is considered transparent in the visible light region. Moreover, NiO is largely used as a catalyst with different n-type semiconductors due its high p-type concentration, high hole mobility and low cost. The existence of NiO enhances the separation of electron and hole pairs via IJSER