Thermal and photochemical vapor deposition of aluminum nitride and gallium nitride

Abstract

Currently, the optical spectrum of the III-V compound semiconductors has been largely confined, with a few notable exceptions, to the visible red-orange to infrared portion of the electromagnetic spectrum ($\sim$650 nm to $\sim$1550 nm). The AlGaN material system may be able to extend this range to the visible green, blue and even ultraviolet regions. The current status of work on the column III-nitride system of compound semiconductors is reviewed with special attention given to the material challenges presently limiting sophisticated device development. Furthermore, the organometallic vapor phase epitaxy (OMVPE) method of growing these materials is discussed in detail in terms of process physics and reactor design and operation.

Fundamental characteristics of the OMVPE growth of AlN and GaN on sapphire substrates at low temperatures and pressures are presented. The precursor adsorption and nucleation behavior was investigated. A model of dissociative adsorption is developed to explain the observed trends. The use of thin AlN buffer layers to improve nucleation and crystallinity of GaN layers is presented and discussed.

The OMVPE growth of these materials was further investigated via the introduction of UV radiation to the chamber during growth. The results of growth under such conditions are presented and discussed. A model of ammonia photolysis is developed and presented, which describes the photochemical growth effects observed and suggests a mechanism of nitrogen incorporation in thermal OMVPE growth of AlN and GaN.