Significant enhancement of breakdown voltage for GaN DHFETs by Si substrate removal

In this paper, we present a study on the substrate removal of AlGaN/GaN/AlGaN double‐heterostructure FETs (DHFETs) on Si (111) substrates by 2 different approaches: a global versus local removal route. We report on the significant enhancement of breakdown voltage (VBD) of DHFETs with only 2 µm thick AlGaN buffer in both cases. In the case of global Si removal, the Si substrate is completely removed and transferred to the sapphire carrier. However, for the local Si removal, the Si substrate is selectively etched only under the source‐to‐drain regions. Before Si removal, VBD saturates at ∼ 700 V at a gate‐drain distance (LGD) ≥ 8 µm: confirming electrical breakdown into the Si substrate. The breakdown voltage is remarkably enhanced after etching away the substrate by either of the techniques. We measure a VBD > 1100 V for devices with LGD ≥ 15 µm with a buffer thickness of only a 2 µm (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)