Breakdown Mechanism of AlGaN/GaN HEMT on 200-mm Silicon Substrate With Silicon Implant-Assisted Contacts

We present an access technology suitable for scaled gallium nitride (GaN) high electron mobility transistor (HEMT) in Ka-band. The comparison between oFF-state characteristics of a silicon implant-assisted contact and a conventional recessed Ti/Al-based Ohmic contact is presented. The transistor with source/drain extension by Si implantation has a low contact resistance with R-C down to 0.4 Omega. mm and a sheet resistance of the implanted layer of 67 Omega/sq. In addition to promising contact performance, transistors with source and drain extension sustain high breakdown voltage (BV) with short dimensions for high-frequency applications. The systematic study of gate-source, gate-drain, and gate length variations shows a new breakdown mechanism for implanted access technology with current flowing beneath the channel leading to an unusual correlation between source-drain spacing and By. With a conventional titanium-alloyed contact, a punchthrough effect is responsible for the By. Cross-sectional transmission electron microscopy and secondary ion mass spectroscopy (SIMS) characterizations on both wafers highlight a degradation of the AlGaN-based back-barrier and a high silicon concentration deep into the epitaxial stack on the implanted wafers indicating a way to improve BV with an adapted process flow.

Automated summary

This study introduces a new contact technology for high-frequency transistors in the Ka-band, showing advantages such as low contact resistance and high breakdown voltage, and explores a new breakdown mechanism. Experimental results demonstrate that silicon implantation has a certain influence on improving breakdown voltage.