Heterostructure Barrier Varactor Diodes for Frequency Multiplier Applications

Abstract: This thesis deals with fabrication, characterisation and modelling of the Heterostructure Barrier Varactor (HBV) diode and its use in frequency multiplier circuits. Different aspects of material structures and frequency multipliers are described. The aim of the work presented is to develop processes to fabricate state of the art HBVs and multipliers in the millimetre and submillimetre wave region. Different III-V material systems for HBVs have been tested. The results of lattice matched and pseudomorphic GaAs/AlGaAs, InGaAs/InAlAs, InAs/AlSb and phosphide containing materials for HBVs are presented. The state of the art material for millimetre and submillimetre wave HBVs is the In0,53GaAs/In0,52AlAs system with a thin AlAs layer (30 Å) in the middle of the barrier. Both simple analytical models and a self-consistent Poisson/Schrödinger approach are used to predict and optimise HBV diodes. The HBVs were evaluated using on-wafer high frequency S-parameter measurements. Finally, an HBV design procedure based on analytical models is proposed.