The off-state gate current in AlGaN/GaN high electron mobility transistors is shown to arise from two parallel gate to substrate tunneling paths: a direct path, and a path via deep traps, which are distributed throughout the AlGaN layer and spread over an energy band. A model to calculate this current is given, which shows that trap-assisted tunneling dominates below T∼500 K, and direct tunneling (thermionic field emission) dominates at higher temperatures. A model fit to experimental results yields the following fabrication process sensitive parameters: trap concentration of ∼1013–1015 cm−3, and trap bandwidth of ∼50%–70% of the barrier height located 0.4–0.55 V below the conduction band edge.

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Articles you may be interested inAnalysis of leakage current mechanisms in Schottky contacts to GaN and Al 0.25 Ga 0.75 N Ga N grown by molecular-beam epitaxy

We provide following important clues for resolving the reverse gate leakage mechanism in AlGaN/GaN high-electron mobility transistors (HEMTs), based on two-dimensional (2-D) simulation and analysis. First, measurement of the gate current-voltage, -, characteristics on devices having different gate structures, passivation layers and interface charges, can reveal the field sensitivity of this mechanism. Second, of the different mechanisms proposed so far, namely-direct tunneling (DT), direct tunneling through a thin surface barrier (DTTSB) and trap-assisted tunneling (TT), DT/DTTSB is sensitive to the 2-D field, while the TT is not. Finally, the DT/DTTSB mechanism appears unlikely, since its 2-D calculations fit the measuredshape, only if we assume a physically unrealistic voltage-variable charge at the interface and/or the TSB layer.