Fabrication and Characterisation of Heterostructure Barrier Varactor Diodes

Report, 1996

This report deals with fabrication and characterisation of Heterostructure Barrier Varactor (HBV) diodes for frequency multiplier applications. The process steps involved are clean-ing, device isolation, passivation, ohmic contacts, thick metal, air-bridge formation, transfer of EPI-layers to copper substrate, and formation of mechanical support for the whisker. These fabrication steps are described in detail. The characterisation techniques of HBVs are described in detail. An equivalent circuit is extracted from on-wafer S-parameter measurements (0,045-50 GHz). In combination with DC-measurements (ohmic contact resistance, I-V characteristic) a large-signal model for frequencies up to the submillimetre wavelength can be extracted. Furthermore, the relative error in extracted varactor parameters from high frequency S-parameter measurements is presented. The results of lattice matched and pseudomorphic GaAs/AlGaAs, InGaAs/InAlAs, InAs/AlSb and phosphide containing materials for HBVs are presented. The best material for millimetre and submillimetre wave HBVs, among those tested, is the In0,53Ga0,47As/In0,52Al0,48As system with a thin AlAs layer (30 Å) in the middle of the barrier.