A semiconductor device with a substrate, a low defect layer formed in a fixed position relative to the substrate, and a barrier layer comprising III-N semiconductor material formed on the low-defect layer and forming an electron gas in the low-defect layer. The device also has a source contact, a drain contact, and a gate contact for receiving a potential, the potential for adjusting a conductive path in the electron gas and between the source contact and the drain contact. Lastly, the device has a one-sided PN junction between the barrier layer and the substrate.