Deposition of CVD diamond onto GaN

A series of experiments have been performed to deposit continuous layers of CVD diamond onto epitaxial GaN films. Such diamond coatings would be useful to enhance the light extraction and heat dissipation in GaN LEDs. A hot filament CVD reactor utilising a CH4/H2 gas mixture was used to deposit the diamond. The substrates consisted of an epitaxial layer of GaN grown onto a sapphire base. It was found that at deposition temperatures > 600 °C the GaN decomposed, evolving gaseous N2 which created pinholes in the growing diamond layer or caused it to delaminate. Lowering the substrate temperature below 600 °C resulted in a prohibitively low growth rate and poor quality diamond. Results will also be presented from a further series of experiments performed using N2 addition to the CH4/H2 gas mixture, with the idea that a high background partial pressure of N2 would slow or prevent the decomposition of GaN.