The impact of initial growth and substrate nitridation on thick GaN growthon sapphire by hydride vapor phase epitaxy

Nucleation and the very initial stages of thin film formation. and their im pact on the GaN thick film properties, were studied for the hydride vapor p hase epitaxy (HVPE) growth technique by affecting changes in the growth sup ersaturation and substrate-GaN interfacial energy. Through these studies. a n optimized growth procedure for HVPE was developed based on separate condi tions for the initiation of growth and the subsequent thick film formation. A two-step growth process was applied to grow GaN on bare sapphire without buffer layers. In the first step, a high growth rate has been used to obta in rapid initial growth and film coalescence on the sapphire substrate. Sap phire nitridation was also used to enhance the initial film growth. In the second step, low growth rate and higher NH3 partial pressures. conditions t hat generally favor a high surface mobility and lateral growth rates, has l ed to improved materials. in terms surface morphology, carrier concentratio n. and optical properties. This study leads to a wider process window for H VPE GaN growth on sapphire substrates relative to the single step processin g approaches. (C) 2001 Elsevier Science B.V. All rights reserved.