In-Situ Transmission Elecron Microscopy (TEM) Study of the Nitridation of Basal Plane Sapphire by Reactive Molecular Beam Epitaxy (RMBE)

Abstract

Group III-nitride thin films are currently of great interest for use in wide-bandgap semiconductor applications including UV lasers and light emitting diodes (LEDs). Sapphire (a-Al2O3) is currently the substrate of choice for the growth of GaN despite a large lattice mismatch. Growth of high quality GaN epilayers typically involves the deposition of a buffer layer of either AIN or GaN at a temperature well below that used for the growth of the active GaN layer. It has been found empirically that nitridation of the sapphire surface with nascent nitrogen prior to growth of the buffer layer results in a substantial improvement in film quality. Using a novel ultra-high vacuum (UHV) in-situ TEM with in-situ RMBE, we have studied the nitridation of the (0001) sapphire surface using transmission and reflection electron microscopy (REM), reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES).An electron-transparent sapphire TEM sample was annealed at 1400°C for 12 hours in flowing oxygen, to form atomically flat surfaces for our investigation.