Influence of Ohmic Contact Resistance on Transconductance in AlGaN/GaN HEMT(GaN-Based Devices,<Special Section>Heterostructure Microelectronics with TWHM2005)

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The correlation between ohmic contact resistivity (ρ_c) and transconductance (g_m) in AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated. To characterize ρ-c precisely, we fabricated a circular transmission line model (c-TLM) pattern adjoined to a field-effect transistor (FET) pattern on an HEMT. By measuring ohmic contact resistance and sheet resistance using the adjoined c-TLM, intrinsic transcon-ductance (g_<m0>), which is not influenced by the source resistance, can be estimated. The g_<m0> thus obtained is between 179 and 206mS/mm. Then, it became possible to calculate the correlation between g_m and ρ_c. We found that ρ_c should be below 10^<-5>Ωcm^2 for the improvement of g_m in AlGaN/GaN HEMT when R_<sh>≒400Ω/□.
2006-07-01