International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Impact Factor (2012): 3.358 Volume 3 Issue 12, December 2014 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Photoconductive Properties of Pulse Plated In 2 Se 3 Films M. Balasubramanian 1 , K. R. Mural 2 1 Vivekananda Institute of Professional Studies, Au Block, Pitampura, Delhi, India 2 ECMS Division, CSIR-CECRI, Karaikudi -6, India Abstract: In 2 Se 3 films were pulse electrodeposited on tin oxide coated glass substrates at different duty cycles for the first time. The films were single phase with crystallite size in the range of 15 – 40 nm. The strain and dislocation density decreased with increase of duty cycle. Post annealing increased the crystallite size from 40 nm to 115 nm. The films exhibited photoconductivity. Keywords: thin films, electronic material, pulse plating 1. Introduction In 2 Se 3 (Indium Selenide, IS) has a direct band gap, with enormous potential utilization in photovoltaic cells and other optoelectronic devices [1]. The In 2 Se 3 consists of some well- known phases, including the layered structure (α-phase), rhombohedral structure (β-phase), defect wurtzite structure (γ-phase) and anisotropic structure (κ-phase). Among these, the γ-phase presents a band gap of 1.8 eV [1], which is suitable for buffer layer in CIS solar cells [2]. The films obtained by a large number of techniques, such as chemical bath deposition [3], electrodeposition [4] and sol gel [5], are composed of at least two low temperature phases. Three preparation methods for growing high performance single phase In 2 Se 3 thin films have been reported until now, including solid state reaction (SSR) [6], molecule beam epitaxy (MBE) [7] and metal organic chemical vapor deposition (MOCVD) [8]. In this work, single phase γ- In 2 Se 3 thin films were deposited by the pulse electrodeposition technique for the first time. In this paper, results obtained on photoconductive properties of In 2 Se 3 films deposited at different duty cycles are presented and discussed. In pulse electrodeposition [10,11] the potential or current is alternated swiftly between two different values. This results in a series of pulses of equal amplitude, duration and polarity, separated by zero current. Each pulse consists of an ON-time (T ON ) during which potential and/current is applied, and an OFF-time (T OFF ) during which zero current is applied. It is possible to control the deposited film composition and thickness in an atomic order by regulating the pulse amplitude and width. They favor the initiation of grain nuclei and greatly increase the number of grains per unit area resulting in finer grained deposit with better properties than conventionally plated coatings. The sum of the ON and OFF times constitute one pulse cycle. The duty cycle is defined as follows: Duty Cycle (%) = (ON time) / (ON time + OFF time) x 100 ----------- (1) A duty cycle of 100% corresponds to conventional plating because OFF time is zero. In practice, pulse plating usually involves a duty cycle of 5% or greater. During the ON time, the concentration of the metal ions to be deposited is reduced within a certain distance from the cathode surface. This so-called diffusion layer pulsates with the same frequency as the applied pulse current. Its thickness is also related to i p , but reaches a limiting value governed primarily by the diffusion coefficient of the metal ions. During the OFF time the concentration of the metal ions build up again by diffusion from the bulk electrolyte and will reach the equilibrium concentration of the bulk electrolyte if enough time is allowed. These variables result in two important characteristic features of pulse plating which make it useful for alloy plating as well as property changes as mentioned earlier. Pulse plating technique has distinct advantages compared to conventional electrodeposition namely, crack free, hard deposits and fine grained films with more uniformity, lower porosity and better adhesion. it is well known that by using pulse current for electrodeposition of metals and alloys it is possible to exercise greater control over the properties of electrodeposits and to improve them by modifying their microstructures [12]. It has been reported that a significant reduction in internal stress could be obtained when pulse current was used, compared to the use of conventional direct current [13]. 2. Experimental Methods In 2 Se 3 films were deposited on titanium and Indium tin oxide substrates at 80°C. The films were deposited at different duty cycles and at a deposition potential of – 0.8 V(SCE). The precursors used were 0.1 M InCl 3 , 0.001M SeO 2 in diethylene glycol. Thickness of the films measured by Surface profilometer was in the range of 400 nm to 800 nm. The films were characterized by x-ray diffraction technique using Philips x-ray unit and CuK α radiation. Optical properties were studied using U3500 Hitachi spectrophotometer. Surface topography was measured by Atomic force microscope 3. Results and Discussion Fig. 1 shows the X-ray diffraction peaks of In 2 Se 3 thin films deposited at different duty cycles. Four peaks corresponding to (110),(006),(116) and (300) of γ-In 2 Se 3 (JCPDS 40-1407). The peaks increase in intensity with duty cycle. The Paper ID: OCT141063 272