Surface-treatment effects of a sapphire substrate by He[sup +]-, Ar[sup +]-, and Xe[sup +]-ion implantations for GaN epitaxial layers

The structural, electrical, and optical properties of GaN epilayers grown on various ion-implanted sapphire(0001) substrates by MOCVD were investigated. GaN or AlN buffer layers and pre-treatment were indispensably introduced before GaN-epilayer growth. The ion-implanted substrate's surface had decreased internal free energies during the growth of the ion-implanted sapphire( 0001) substrates. The crystal and optical properties of the GaN epilayers grown in ion-implanted sapphire(0001) substrates were improved. Also, an excessively roughened and modified surface caused by ions degraded the GaN epilayers. Not only the ionic radius but also the chemical species of implanted sapphire(0001) substrates improved the properties of the GaN epilayers grown by MOCVD. It is obvious that the ion-implanted pre-treatment of sapphire(0001) substrates can be an alternative pre-treatment procedure for GaN deposition and has the potential to improve the properties of the GaN epilayers on sapphire(0001) substrates.