On the origin and suppression of parasitic channel in AlN/GaN/AlGaN back barrier RF devices

This work investigates the origin and physical location of a parasitic conduction path in GaN devices incorporating an AlGaN back barrier (BB) through a combined approach of calibrated Technology Computer-Aided Design (TCAD) simulations and experimental C–V and I–V measurements on Schottky diodes and high electron mobility transistors (HEMTs). The phenomenon was observed to directly depend on the carbon doping in the AlGaN BB, which significantly affects its resistivity. Insufficient doping leads to an uncompensated n-type BB, enabling electron accumulation at the GaN channel/BB interface and the formation of a parasitic charge sheet. Conversely, high carbon concentrations result in a semi-insulating behavior, preventing vertical leakage current and thus effectively suppressing the conduction path. This mechanism, which is not intrinsic to the heterostructure but emerges from inadequate doping compensation, contrasts with previous hypotheses invoking defect-mediated hopping. This study highlights the critical role of BB resistivity, not just polarization design, in determining vertical confinement. These findings offer valuable insights into the optimization of BB doping strategies for leakage control and enhanced electron confinement in next-generation GaN HEMTs.