Investigation of Au-free AlGaN/GaN HEMT on Silicon with substrate transfer process: From Ohmic contacts to RF performance

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PhD; 2022; Centre for nano science and engineering

The technological importance of III-nitride based high electron mobility transistors (HEMTs) for power switching and RF applications is growing rapidly, owing to two advantageous electrical properties. While high sheet carrier concentration and mobility of charge carriers confined in the 2DEG translate to high current levels, high bandgap of III-N based materials leads to high breakdown voltage. However, III-N based devices have not been able to penetrate the semiconductor market as deep as Silicon based technologies. High costs associated with the epitaxial growth of the III-N based HEMT stack on hetero-substrates like Si, SiC or Sapphire as well as high costs associated with III-N based device processing are the two key reasons. While development of III-N growth on Silicon can potentially bring down the net cost associated with growth, CMOS compatible fabrication of III-N based devices can reduce the cost associated with device processing as this will permit the processing of III-N devices in existing CMOS fab lines. The most important difference between conventional and CMOS compatible processing of III-N based devices is the absence of gold (Au) in CMOS process, since Au has high diffusion rates in Si even at moderate temperatures and it also acts as a deep impurity in Silicon leading to formation of electrical trap levels in Silicon bandgap leading to degradation in device performance.