Planar Heterostructure Barrier Varactor Diodes for Millimetre Wave Applications

Doctoral thesis, 1999

This thesis deals with fabrication, characterisation and modelling of the Heterostructure Barrier Varactor (HBV) diode and its use in frequency multiplier applications. Different aspects of material structures and frequency multipliers are described. The aim of the work presented is to develop design methods and processes to fabricate state-of-the-art planar HBVs and multipliers in the millimetre and submillimetre wave length region. Results from AlGaAs HBV frequency tripler measurements are presented. Simulations and cooled measurements show that excessive conduction current due to self-heating degrades the multiplier efficiency. A new design of planar GaAs-based HBVs with reduced thermal resistance and series resistance have been fabricated. A state-of-the-art performance of 4,8% efficiency and an output power of 4 mW at 246 GHz was achieved. A novel fabrication process where HBV diodes are fabricated on a copper substrate is proposed. This reduces thermal resistance and parasitic resistance without degrading the electrical characteristics. A 141 GHz quasi-optical HBV tripler is presented. A peak flange-to-flange efficiency of 8% and an output power of 11,5 mW was achieved. 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/Schroedinger approach are used to predict and optimise HBV diodes. Finally, a simple quick-design method for calculation of optimum embedding impedances, optimum conversion efficiency and pump power for HBV triplers are presented.