American Journal of Condensed Matter Physics 2015, 5(2): 51-55 DOI: 10.5923/j.ajcmp.20150502.02 Effect of Thickness on the Structural and Electrical Properties of Spray Pyrolysed Lead Sulfide Thin Films Mohammad Ghaffar Faraj Department of Physics, School of Science, Faculty of Science and Health, University of Koya, Koya, Iraq Abstract Lead sulfide (PbS) thin films of different thicknesses ranging from 100 to 300 nm were prepared on glass substrates at 325℃ by chemical spray pyrolysis(CSP) technique. PbS thin films were prepared using a solution of Lead nitrate and thiourea. The structural properties were carried out by X-ray diffraction (XRD). X-ray diffraction patterns reveal that the films exhibit the cubic rock salt (NaCl) type structure. The crystalline grain sizes of the films increase with increasing film thickness. The root mean square (RMS) roughness of the films was measured using scanning tunneling microscope (STM). The root mean square roughness of the films increases as the film thickness increases. At room temperature, electrical resistivity and charge-carrier concentration of the PbS film varies from 53.72x10 3 to 1.1 x10 3 Ω.cm and 2.98 × 10 10 to 1.2× 10 12 cm − 3 , respectively. Keywords Lead Sulfide, Chemical Spray Pyrolysis, Thin Film, Semiconductor 1. Introduction Among the IV-VI semiconductors, PbS thin films have been used in a lot of applications, including electronic and optoelectronic devices [1-3]. PbS is an important direct narrow gap semiconductor material with band gap energy of 0.4 eV and has a cubic lattice with unit cell face center cube [4-6]. Many techniques have been reported for the deposition of PbS thin films such as chemical bath deposition (CBD) [7], electrodeposition (ED) [8], Chemical spray deposition (CSP) [9] and thermal evaporation technique [10]. Of the various techniques, spray technique is an attractive method because large-area films with good uniformity can be grown at a low cost [10, 11]. In this present work, an attempt has been made to study the structural and electrical properties of the PbS thin films with different thicknesses ranging from 100 to 300 nm grown by Chemical Spray Pyrolysis technique on glass substrate. An effort has also been made to see the effect of thickness on structural and electrical properties of prepared films. 2. Experimental Detail 2.1. Glass Substrate Cleaning * Corresponding author: mohammad.ghaffar@koyauniversity.org (Mohammad Ghaffar Faraj) Published online at http://journal.sapub.org/ajcmp Copyright © 2015 Scientific & Academic Publishing. All Rights Reserved Glass slides with the dimensions of 75 × 25 ×2 mm were used as substrates. In the (CSP) technique, cleaning the substrate surface is very important due to its effect on adherent thin film properties. Firstly, the substrates were cleaned by alcohol for 10 min to remove contamination. After the cleaning process, all of the substrates were rinsed with distilled water. The samples were dried with nitrogen (N 2 ) gas. 2.2. Materials Lead (II) acetate trihydrate (Pb(CH 3 CO 2 ) 2 3H 2 O; 99.999%), Thiourea (CS (NH 2 ) 2 ), 99.0%) were acquired from Acros Organics. 2.3. Preparation of PbS Solutions A typical PbS solution procedure involves: 1. Thiourea solution [CS (NH 2 ) 2 ]: This solution was prepared with molarities (0.1M), from solving (0.761gm) of thiourea in (100ml) of distilled water and was marked solution 1.This solution was vigorously stirred using a magnetic stirrer about 10 minutes. 2. Lead Nitrate solution [Pb(CH 3 CO 2 ) 2 · 3H 2 O]: This solution was prepared with molarities (0.1M), from solving (2.78gm) of lead acetate in (100ml) of distilled water and was marked Solution 2. This solution was vigorously stirred using a magnetic stirrer about 10 minutes. A solution 1 was added to solution 2 and vigorously stirred using a magnetic stirrer and was marked solution 3. PbS thin films were deposited from a solution 3 by chemical spray pyrolysis technique on glass substrate. In