Microwave Characterization of GaN-on-Si Heterostructure Loss and 2DEG as a Conductor

Abstract

GaN devices have been dubbed ‘the future of high frequency, high power applications’ due to the material properties of GaN that promises a clear advantage over competing technologies. Heteroepitaxial growth of AlGaN/GaN on Si has gained popularity in the recent years due to cost considerations and opportunity of on-chip integration of GaN and Si based devices. This work investigates the microwave properties of the GaN-on-Si substrate and the 2DEG in order to establish their limitations and advantages to set a framework for epitaxial growth and RF design efforts.

In this study the broadband characterization of GaN-on-Si is realized for 6 – 20 GHz frequency range. Dielectric loss of epi-layers is extracted through a differential study of CPWs on different thicknesses of GaN, AlGaN and AlN grown via metalorganic chemical vapor phase deposition (MOCVD) on Si. Changes in effective loss tangent, conductivity and dielectric loss tangent are reported. Where prior reports place the majority of dielectric loss at the Si/AlN interface, it is found that the top GaN layer has a bigger impact on the polarization losses, whereas the AlN is a stronger contributor to the overall conduction losses.

2DEG transmission properties over the 6 - 20 GHz range are also investigated and reported for the first time. Loss of 2DEG as a transmission line is found to be decreasing with frequency. The possible reasons for this loss behavior are examined. 2DEG ohmic contact geometry and its parasitics are also investigated to provide important design parameters for RF device design.