A preferred method of optimizing a Ga-nitride device material structure for a frequency multiplication device comprises: determining the amplitude and frequency of the input signal being multiplied in frequency; providing a Ga-nitride region on a substrate; determining the Al percentage composition and impurity doping in an AlGaN region positioned on the Ga-nitride region based upon the power level and waveform of the input signal and the desired frequency range in order to optimize power input/output efficiency; and selecting an orientation of N-face polar GaN or Ga-face polar GaN material relative to the AlGaN/GaN interface so as to orient the face of the GaN so as to optimize charge at the AlGaN/GaN interface. A preferred embodiment comprises an anti-serial Schottky varactor comprising: two Schottky diodes in anti-serial connection; each comprising at least one GaN layer designed based upon doping and thickness to improve the conversion efficiency.