THE FABRICATION AND PERFORMANCE OF PLANAR-DOPED BARRIER DIODES AS 200GHZ SUBHARMONICALLY PUMPED MIXERS

The PDB (planar doped barrier) diode consists of a p+ doping spike bet ween two intrinsic layers and n+ ohmic contacts. Such devices can have an anti-symmetric current vs. voltage characteristic. The capacitance is approximately constant with the applied voltage, and the barrier h eight and device capacitance are easily adjustable. These characterist ics make the PDB a candidate for millimeter- and submillimeter-wave su bharmonic mixers. We have fabricated 2 and 4 mum diameter diodes with different barrier designs using GaAs epi-layers. The devices are plana rized using an air-bridge and a surface channel etch. After completely removing the substrate, the devices are mounted on a quartz substrate to reduce parasitic effects. Diced diodes were tested as subharmonic mixers around 200 GHz in both a quasi-optical planar wideband subharmo nic receiver and a planar-diode waveguide-mixer. The quasi-optical mea surements show that a 0.23 V (and 0.4 V) barrier height GaAs diode wit h 2.0 muA (and 5 nA) of saturation current gives a DSB conversion loss of 10.8 dB (and 9.5 dB) and a DSB noise temperature of 3795-degrees-K (and 2450-degrees-K). The waveguide mixer measurements were made with a similar 0.23 V barrierheight PDB. Such a mixer has a minimum conver sion loss of 10.2 dB and noise temperature of 3570-degrees-K, and requ ires only 1.2 milliwatts of available LO power.