Effect of deposition conditions on properties of nitrogen rich-InN nanostructures grown on anisotropic Si (110)

Abstract

Nanocrystalline InN were fabricated on anisotropic silicon [Si(110)] substrates by reactive radio frequency sputtering. The effects of deposition conditions on the InN film characteristics were comprehensively studied. The films were prepared using different argon and nitrogen plasma ratios under 8×10⁻³ mbar at different temperatures and RF powers. X-ray diffraction measurements confirmed that all deposited films are wurtzite nanocrystalline InN films with (101) preferred growth orientation. All of the samples obtained under different deposition conditions were slightly N rich. For optimized deposition conditions, InN film on Si(110) substrate shows smooth surface with root-mean-square roughness around 2 nm. The optical properties of InN layers were examined by micro-Raman and FTIR spectroscopy at room temperature. The A₁(TO) and E₁(TO) modes observed were a consequence of the wurtzite nanocrystalline nature of RF-sputtered films.

Introduction

Indium nitride (InN) has a wurtzite crystal structure with a small band gap of 0.7 eV [1]. InN is an interesting semiconductor material because of its potential applications in optoelectronic devices, such as high efficiency solar cells, high electron mobility sensors, and transistors [2], [3], [4], [5]. However, InN has received less attention compared with gallium nitride (GaN) and aluminum nitride primarily because of difficulties inherent in the preparation of its stoichiometric form. In addition, high-grade single crystal InN is difficult to grow due to its low dissociation temperature and less suitable substrates. Due to its low dissociation temperature, InN film should deposit at low temperatures to avoid N atom re-evaporation [6], [7]. Reactive sputtering is one of the most promising techniques of producing InN from the viewpoint of low-temperature film growth. InN layer synthesis on sapphire and glass substrates using reactive sputtering has been previously reported [8], [9], and InN deposition on different Si substrate orientations has been recently investigated [10], [11], [12], [13]. The anisotropic Si(110) surface offers a unique orientation for GaN films compared to Si(001) where it can decrease the defect density and tensile stress for film cracking [14].

Nevertheless, few organized studies of nanocrystalline InN grown on anisotropic Si (110) substrate by radio frequency (RF) sputtering have been reported thus far [15], [16]. In the current study, InN nanostructures were successfully deposited by reactive RF magnetron sputtering on anisotropic Si(110) substrates. The structure and optical properties of the resulting films were investigated under various deposition gas concentrations, RF powers, and substrate temperatures.