Deposition of nanocrystalline CuS thin film from a single precursor: Structural, optical and electrical properties

Abstract

Nanocrystalline CuS thin films were fabricated using a metal organic deposition technique taking Cu(SOCCH₃)₂Lut₂ as the precursor. X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), UV–vis absorption spectroscopy, photoluminescence spectroscopy (PL) and Raman spectroscopic techniques were applied for characterization and found that the deposited CuS films were of ‘covellite’ phase with an average particle size of 18 nm. Optical measurements showed significant amount of “blue shift” in the band gap energy. Hall measurements of the films showed p-type conduction nature with a carrier concentration in the range 10¹²–10¹³ cm⁻³.

Introduction

In the past few decades, there has been an increasing interest in semiconducting chalcogenide thin films, due to their various applications in cutting edge science and technology. Copper sulfide is an important p-type semiconductor which has several applications in the fields of solid state solar cells [1], [2], [3], electro conductive coatings [4], [5], electrodes [6] and also in catalysis [7]. Coating of CuS on glass windows (architectural) is also used as a selective radiation filter [8] in warm climates. The covellite form of copper sulfides shows metallic conductivity and presently, it was found to show superconductivity at 1.6 K [9]. Generally, copper sulfide can easily form a series of nonstoichiometric compounds, Cu_xS (x = 1–2) like chalcocite (Cu₂S), djurleite (Cu_1.96S), digenite (Cu_1.85S), anilite (Cu_1.75S) and covellite (CuS) [10], [11] with a crystal structure varying from orthogonal to hexagonal. The abundant component and crystal phase of copper sulfide results in unique properties [12], [13], [14], [15], [16], [17], [18]. On the basis of the versatile applications of the Cu_xS material, a large effort has been focused on the synthesis of Cu_xS crystallites with different morphologies, including plate-like [19], [20], tubular [21], [22], [23], [24], [25], [26], [27], spherical [28], flower-like [29], rod-like structures [30], flake-like [31], [32], [33], [34], and so on. The widely used methods for the deposition of Cu_xS films are chemical bath deposition (CBD) technique [1], [2], [3], [4], [35], spray pyrolysis [36], [37], atomic layer deposition (ALD) [38], chemical vapor deposition (CVD) [39] and vacuum evaporation [38]. Except these, Cu_xS films can also be deposited using metal organic deposition (MOD), high temperature solution growth route, microwave and solid state reaction technique, etc. We have used the MOD technique, science it is a powerful, inexpensive and comparatively less studied technique.

The purpose of the present work is to prepare efficient CuS thin films by a simple MOD technique using Cu(SOCCH₃)₂Lut₂ as a single source precursor (SSP), and to study their structural, optical and electrical properties.