Growth of GaN high-electron mobility transistors on 150 mm silicon demonstrated

Growing low sheet resistivity transistors on 150 mm silicon wafers has been achieved by a European research group and presented at the 13th International Conference on Metal Organic Vapor Phase Epitaxy in Japan.

IMEC, a nanoelectronics and nanotechnology research institute grew AlGaN /GaN high-electron mobility transistors (HEMPTs) on the wafers.

The AlGaN and GaN layers were grown in IMEC's 150 mm metal-organic chemical vapour-phase epitaxy system that allows the institute to offer access to its AlGaN/GaN epiwafers in a service mode to laboratories and partner companies.

Good uniformity has been obtained for the growth of HEMTs on 150 mm Si wafers. HEMT structures with a sheet resistivity down to 272 +/- 5 square and a standard deviation down to 1.9% (edge excluded) have been demonstrated.

The process overcomes current problems associated with the growth of high-quality epitaxial GaN layers on Si. These problems result from the high lattice mismatch and the large difference in thermal expansion coefficient between Si and GaN. An AlGaN buffer layer has been successfully introduced to provide compressive stress in the top GaN layer. This, in combination with an IMEC propriety in-situ Si3N4 passivation layer, results in HEMT devices on Si.

Due to the lack of commercially available GaN substrates, GaN heterostructures are grown mainly on sapphire and silicon carbide. Si is a suitable alternative due to its very low cost compared to sapphire and SiC. Other benefits include the acceptable thermal conductivity of Si (half of that of SiC) and its availability in large quantities and large wafer sizes.

The high-quality epitaxial AlGaN and GaN layers were grown in the institute's 150 mm metal-organic chemical vapour-phase epitaxy Thomas Swan close-coupled showerhead reactor system, in the framework of a European Space Agency project called Epi-GaN.

"This reactor is a very valuable extension of our existing 3x2" system, as it increases both growth capacity and wafer size (up to 150 mm). The results prove the capability of IMEC to grow HEMT epiwafers with excellent quality, good uniformity and high reproducibility." said Marianne Germain, director of IMEC's Efficient Power Project.

GaN has capabilities for power, low-noise, high-frequency, high-temperature operations, even in harsh environment (radiation).