A process for recovering unreacted olefin in a polyolefin manufacturing process comprising the treatment of a purge bin vent gas. In the growth step, at least one element selected from the group consisting of C, Mg, Fe, Be, Zn, V, and Sb is added as an impurity element by at least 1\xd71017 cm\u22123 to the first group III nitride semiconductor layer. Each of the two regions has a corresponding fixed transistor threshold voltage, a corresponding fixed transistor body bias, and a corresponding fixed supply voltage.