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

Nucleation and the very initial stages of thin film formation. and their impact on the GaN thick film properties, were studied for the hydride vapor phase epitaxy (HVPE) growth technique by affecting changes in the growth supersaturation and substrate-GaN interfacial energy. Through these studies. an optimized growth procedure for HVPE was developed based on separate conditions 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 obtain rapid initial growth and film coalescence on the sapphire substrate. Sapphire nitridation was also used to enhance the initial film growth. In the second step, low growth rate and higher NH3 partial pressures. conditions that generally favor a high surface mobility and lateral growth rates, has led to improved materials. in terms surface morphology, carrier concentration. and optical properties. This study leads to a wider process window for HVPE GaN growth on sapphire substrates relative to the single step processing approaches. (C) 2001 Elsevier Science B.V. All rights reserved.