12% efficiency and 9.5 dBm output power from InP-based heterostructure barrier varactor triplers at 250 GHz

9.5 dBm and 12.3% maximum efficiency demonstrated for a 250 GHz Heterostructure Barrier Varactor (HBV) tripler. These state-of-the-art performances can be explained by the highly nonlinear capacitance-voltage characteristics of InGaAs-InAlAs-AlAs diodes having a zero-bias capacitance of 1fF//spl mu/m/sup 2/, a capacitance ratio of 6:1 and a breakdown voltage of 12 V for two barriers. Also the potential of nonlinear transmission lines for harmonic multiplication were investigated for vertically and laterally stacked devices.