a iii - nitride based field effect transistor obtains improved performance characteristics through manipulation of the relationship between the in - plane lattice constant of the interface of material layers . a high mobility two dimensional electron gas generated at the interface of the iii - nitride materials permits high current conduction with low on resistance , and is controllable through the manipulation of spontaneous polarization fields obtained according to the characteristics of the iii - nitride material . the field effect transistor produced can be made to be a nominally on device where the in - plane lattice constants of the material forming the interface match . a nominally off device may be produced where one of the material layers has an in - plane lattice constant that is larger than that of the other layer material . the layer materials are preferably inalgan / gan layers that are particularly tailored to the characteristics of the present invention .