Studies of AlN grown by MOVPE for electronic and optoelectronic applications

Abstract

In recent years, AlN has attracted considerable attention as a potential candidate for short wavelength optoelectronic and high temperature/high voltage electronic devices because of its widest bandgap (almost equal 6.01eV) among the group-III nitrides and extremely outstanding chemical and thermal stability under hostile environment. However, the epitaxial growth of AlN having excellent crystalline quality, smooth surface morphology, and good spectroscopic properties - as required for device fabrication - is still a big challenge. One major problem during the epitaxial growth of AlN and high Al content AlGaN is the parasitic gas-phase pre-reactions between ammonia and the metalorganic Al precursors. Another problem is the emergence of high density of threading dislocations due to a large lattice mismatch between the foreign substrate (sapphire) and the subsequently grown AlN epilayer. In this thesis, an epitaxial growth methodology is developed to obtain a very high quality AlN epilayer on c-plane sapphire substrate using MOVPE. The structural and spectroscopic properties of AlN epilayers have been investigated using X-ray, AFM, TEM, and cathodoluminescence measurements. In group-III nitrides, Si is used as an n-type dopant. In this work, we have investigated the effects of Si doping on the structural, spectroscopic and electrical properties of AlN and studied the doping limitations. Finally, high Al content AlGaN epilayers and AlN/AlxGa1-xN heterostructures have been grown and investigated for potential AlN based electronic and optoelectronic devices.