Growth of AlN and TiN Structures by Plasma-Enhanced Pulsed Laser Deposition
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Growth of AlN and TiN Structures by Plasma-Enhanced Pulsed Laser Deposition Edward Poindextera, Yan Xinb and Steven M. Durbina,c a Department of Electrical and Computer Engineering, Florida A&M University and The Florida State University, Tallahassee, FL 32310 USA b National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA c Department of Electrical & Electronic Engineering, University of Canterbury, Christchurch, NEW ZEALAND ABSTRACT Nitride materials are of interest for a wide variety of applications, including wearresistant coatings, insulating layers, high-temperature semiconductor devices, and shortwavelength emitters and detectors. TiN and AlN appear to be particularly amenable to crystalline thin film deposition, with stoichiometric material easily obtained even without the use of active nitrogen species. This paper describes the growth of crystalline AlN and TiN thin films on silicon and sapphire substrates using a KrF excimer laser (λ = 248 nm) to ablate elemental metallic targets, and an inductively-coupled RF plasma source to supply active nitrogen species. Growth was monitored in-situ using reflection high-energy electron diffraction (RHEED), and films were characterised using fourier-transform infrared spectroscopy (FTIR) and electron microscopy techniques. Optimised growth conditions led to single-crystal growth of TiN on both substrates, but only polycrystalline AlN was formed directly. Use of a TiN buffer layer on (0001) sapphire led to the successful growth of a single-crystal AlN layer as confirmed by RHEED and high-resolution transmission electron microscopy (HRTEM). INTRODUCTION Recent success in the fabrication of blue-emitting devices based on GaN thin films has re-energised interest in the family of wide-bandgap nitride materials. Well-known for their tribological properties, these materials also possess a great deal of potential for use in optical and electronic applications. Particularly interesting is the binary compound AlN, which is characterised by a bandgap energy on the order of 6 eV, comparable to that of diamond. There are several different techniques currently in use for the growth of nitride materials, although there remains a need for the development of low-cost methods suitable for low-temperature growth. Pulsed laser deposition (PLD) is widely accepted as a reliable and economical technique for growth of high critical temperature superconductor (HTS) thin films. In recent years, it has also been used to deposit a variety of materials, including semiconductors, metals and polymers. Characterised by growth rates comparable to other thin film deposition techniques, PLD is also capable of monolayer thickness control. The basic technique consists of using a pulsed laser focused to an energy density on the order of 1 J/cm2 to ablate a target having the desired composition. Ultraviolet wavelengths are typically employed to minimise the ejection of particulates from the target, and the ablation plume consists of a mixture of free electrons, neutral atoms and ionised species [1
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