Toward Integration of Dense, Contiguous, and Low-Stress Capping Diamond on GaN/AlGaN Layer Using Two-Step Growth Process

The integration process of capping diamond layer on GaN has been systematically studied for the thermal management of GaN HEMTs. The whole deposition process includes with electrostatic absorption seeding and two-step growth. The electrostatic adsorption seeding method, utilizing a zeta potential of -50 mV, promotes the formation of dense and uniform diamond nucleation sites without voids. After seeding process, a two-step deposition process is further designed to grow high-quality capping diamond layer. At the nucleation progress, higher methane content and lower temperature condition are introduced to avoid plasma-induced GaN decomposition and etching. At the growth stage, lower methane content and higher temperature condition are designed to improve crystalline quality and stress characteristics of the capping diamond layer. Continuous, uniform and adherent diamond passivation layers are successfully deposited. The components and stress distribution characteristics of cross-sectional interface have been analyzed after deposited diamond layer in detail. Ultralow stress value of diamond and GaN layer has been obtained with directly deposited diamond passivation layers on AlGaN/GaN layer. The compressive stress of diamond film is reduced to 0.09 GPa. And a low tensile stress value of similar to 0.3 GPa is obtained for the GaN layer after deposited capping diamond. All the results show that high-quality AlGaN/GaN layers with passivated diamond layers have been fabricated.