A III-nitride heterojunction power semiconductor device having a barrier layer that includes a region of reduced nitrogen content. Each chip has a one or more diodes. The compound AC generator includes a shaft, and a permanent magnet generator configured to be driven by the shaft to generate an AC power signal. These procedures increase the number of nucleation sites, and grain size of the copper layer, resulting in less damage to the treated copper layer, as a result of a subsequent CMP procedure, when compared to counterpart copper layers, subjected to the same CMP procedure, however without experiencing the overlying, thin compressive layer, followed by the low temperature anneal.