Effect of GaN Channel Layer Thickness on DC and RF Performance of GaN HEMTs With Composite AlGaN/GaN Buffer

The effects of GaN channel layer thickness on dc and RF performance of AlGaN/GaN high-electron mobility transistors (HEMTs) with a state-of-the-art composite AlGaN/GaN (1/1 mu m) buffer were systematically investigated. Although HEMTs with a thick GaN channel layer exhibit slight degraded dc and RF small-signal performance associated with short-channel effects, they demonstrate significantly enhanced OFF-state breakdown voltage and RF large-signal performance. The 1-mm HEMTs with a 150-nm-thick GaN channel layer feature a 1.4 dB higher saturated POUT and about 10% higher PAE than that with a 50-nm-thick GaN channel layer, in both Classes AB and B operation conditions. Pulse I-V characterization reveals that the buffer-related current collapse is also suppressed in the thick GaN channel sample as compared with the thin one, suggesting that a thick GaN channel layer will not only reduces the deep traps in the channel, but also reduces the electron capture probability by deep traps in the composite AlGaN/GaN buffer. The selection of a proper GaN channel layer thickness is thus of great importance to the designation of GaN-based power amplifiers for various applications.