Influence of Diamond CVD Growth Conditions and Interlayer Material on Diamond/GaN Interface

Abstract

In this study we present the diamond deposition on AlGaN/GaN substrates focusing on the quality of the diamond/GaN interface. The growth of diamond films was performed using microwave chemical vapour deposition system in different gas mixtures: standard CH4/H2 (at low and high ratio of CH4 to H2) and addition of CO2 to CH4/H2 gas chemistry. The diamond films were grown directly on GaN films either without or with thin interlayer. As interlayer, 100 nm thick Si3N4 was used. Surprisingly, in the case of standard CH4/H2 gas mixture, no diamond film was observed on the GaN with SiN interlayer, while adding of CO2 resulted in diamond film formation of both samples with and without SiN interlayer. Moreover, adding of CO2 led to higher growth rate. The morphology of diamond films and the quality of the diamond/GaN interface was investigated from the cross-section images by scanning electron microscopy and the chemical character (i.e. sp3 versus sp2 carbon bonds) was measured by Raman spectroscopy.