(604a) Engineering AlN Thin Films by Atomic Layer Deposition On Wide Bandgap Semiconductors As Gate Dielectric

Wide bandgap semiconductors, such as SiC and GaN, are known as base materials in electronic devices operating under high temperatures and high electric field. Aluminum nitride (AlN) is a promising interfacial layer or dielectric material for SiC and GaN due to its material properties, such as wide bandgaps, similar atomic arrangement and small lattice mismatch (1.3% and 2.6%). In order to grow high quality AlN thin films for the applications, atomic scale controllability during the growth dictate the electrical performance of the synthesized materials.  To achieve atomic controllability, atomic layer deposition (ALD) is used to synthesize AlN thin layer on SiC, GaN and Si to assess the possibility to extend this deposition method to nitride growth and how the substrate properties affect the interface quality and corresponding electrical properties of the synthesized film

The AlN thin films were synthesized by using trimethylaluminum (TMA) and blue grade ammonia (NH₃) at 400~600^oC, with the surface structure during the deposition monitored via in-situ RHEED. The growth rate was 0.5~2Å/cycle as a function of the growth temperature.  The surface composition, including the impurities, was related to the deposition temperature, verified by in-situ x-ray photoelectron spectroscopy (XPS). The surface of the films was studied by transmission electron microscopy (TEM) and atomic force microscope (AFM) and found to be conformal because the rms value was found to be about the same as that of the substrate surface roughness. The capacitance/conductance-voltage characteristics were measured to determine the dielectric constant of the ALD film and interpret the interface states density, which were 8 and on the order of 10¹² cm^-2eV^-1, respectively, comparable to that reported for AlN grown by MBE.