Epitaxial Growth of A1N by Plasma Source Molecular Beam Epitaxy

Abstract

A1N films were grown on Si (111), Si (100), and Al₂O₃ (0001), and Al₂O₃ $\left( {1\bar 102} \right)$ substrates by plasma source molecular beam epitaxy (PSMBE). This deposition technique uses a magnetically enhanced hollow cathode, lined with an aluminum target material. A nitrogen plasma is formed within the hollow cathode. A low energy flux of sputtered aluminum and nitrogen (partially dissociated) stream out of the cathode to the substrate. The energy of the source ions can be controlled by a bias ring. AlN film quality is correlated with substrate temperature and bias effects. The substrates were continuously rotated during growth and the temperature was varied from 400°C to 800°C. The acceleration bias was varied between 0V to -20 V dc. Epitaxial growth of AlN on Si(l 11) occurred with growth temperatures above 500°C. A buffer layer of AlN grown at 400°C on Al₂O₃ followed by growth at temperatures higher than 500°C resulted in high quality AlN films with preferred orientation. The crystalline quality and composition of the deposited films were characterized by x-ray diffraction, atomic resolution TEM, and atomic force microscope. The thermal conductivity of the films were characterized by mirage thermal characterization technique. Optical properties were analyzed by spectroscopic ellipsometry.