Lateral charge spreading and device-to-device coupling in C-doped AlGaN/GaN-on-Si wafers

We demonstrate experimental evidence of lateral charge transport spreading up to 2 mm beyond the active area of a biased GaN HEMT device and resulting in changes in R _ON in adjacent devices. Guarded surface leakage test structures have been used to show that the lateral leakage path lies within the bulk of the buffer and is not a surface effect. This behaviour is consistent with the previously reported accumulation of positive charge at the interface between the carbon doped GaN layer and the (Al)GaN strain relief layers. The resulting time-dependent charge storage impacts unprobed device performance and can be a significant concern for on-wafer reliability measurements, or more seriously, system integration where devices share the same epitaxy.