International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | March -2017
p-ISSN: 2395-0072
www.irjet.net
Significance of substrate temperatures on the deposition of ZnGa 2Se4 thin films by flash evaporation technique V. D. Dhamecha*1, B. H. Patel1, P. B. Patel1 and V. A. Patel2 1 Department 2
of Electronics, Sardar Patel University, Vallabh Vidyanagar 388120, Gujarat, India SICART-CVM, DST Sponsored Research Centre, Vallabh Vidyanagar 388120, Gujarat, India
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Abstract - Bulk ZnGa2Se4 was grown by melt-growth
In the present investigation, we report in details the study of the deposition of ZnGa2Se4 thin films by flash evaporation technique and the significance of substrate temperatures on the structural, morphological and optical characteristics like orientation of the films, elemental composition and optical band gap.
technique, using the stoichiometric mixture of constitute elements. The ternary compound semiconductor ZnGa2Se4 thin films deposited by flash evaporation technique. The grown material was characterized by x-ray diffraction technique. The influence of the substrate temperature on the structural, morphological and optical properties of the films has been studied. The films deposited at substrate temperature range 573 K ≤ Tsub ≤ 673 K have been identified to be single phase, stoichiometric and polycrystalline with having (112) and (204, 220) preferred orientations. The topography and the surface roughness of films were studied by Atomic Force Microscopy. Optical analysis of the films revealed that band gap energy increases with increase in the substrate temperatures.
2. Experimental 2.1 Growth of Material A single phase, polycrystalline ingot of ZnGa2Se4 was grown by direct fusion of stoichiometric amounts of their constituent elements (Zn, Ga, and Se of purity 99.999%) in a sealed evacuated quartz ampoule at high vacuum. Then the ampoule was kept in a programmable rotating furnace. The temperature of the furnace was programmed with increasing rate of 100 K/h until it reach upto the 1423 K melting point of ZnGa2Se4 [12] and was kept constant for 3 hours. During this constant period of time, the ampoule was rotated at the rate of 10 rpm. The rotation for three hours duration by mechanical shaking of the mixture ensures the high homogeneity and quality of the compound. Then, the furnace was cooled down in steps until it reached the subsequent temperatures 873 K, 773 K and 643 K and kept constant for 1 h at every stage [8]. The ampoule was finally cooled down to the room temperature. The ingot of reddish color obtained by breaking the ampoule which was finely powdered with a mortar for X - ray study.
Key Words: Flash evaporation, Transmission Electron Microscopy, Stoichiometry, Atomic Force Microscopy, Optical Band gap
1. INTRODUCTION The Zinc tetraselenodigallate (ZnGa2Se4) is member of the IIIII2-IV4 group semiconducting compounds. This ternary group have increasing interest because of their wide applications such as memory devices, narrow band optical filters, nonlinear optical devices, schottky diode, ultra – violet photodetectors, etc. [1][2][3][4]. Most of these compounds form in tetragonal type structure [5][6][7]. Polycrystalline ZnGa2Se4 was first synthesized by Hahn et al. [8]. Structural and optical properties of the ZnGa 2Se4 thin films by thermal evaporation technique was reported by Fadel et al. [9]. ZnGa2Se4 can be used for phase change memories [10]. The current-voltage characteristics of ZnGa2Se4 heterojunction diode was studied by Yahia et al. [11]. Although, to our knowledge the influence of substrate temperatures on the structural and optical properties of ZnGa2Se4 thin films has not yet been reported.
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2.2 Growth of Thin film ZnGa2Se4 thin films were grown by flash evaporation technique. The source material was single phase ZnGa2Se4 with average grain size of ~ 100 µm. The evaporant charge was reduced to the average grain size for complete evaporation of the material effectively to produce stoichiometric compound thin film. A flash evaporation system consists of controllable vibratory feeder system attached with a relay. An electrical pulse applied to the relay will drop the material from the feeder into the quartz crucible placed into a tungsten helical wire. The evaporant charge (~ 5 mg) was dropped step by step in to the preheated quartz crucible in order to deposit stoichiometric thin films. The substrates were placed in the middle of the cylindrical heater
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