The output conductance in GaAs air-gap MESFETs

Theoretical studies have led to the conclusion that substrate injection into the epilayer underneath the channel plays a major role in the output conductance of the GaAs MESFET. The authors believe that vacuum (or an air gap) itself would be the best layer to have underneath the channel. They propose the technology to achieve such devices. This technology would also eliminate the undesirable sidegating and backgating effects in GaAs MESFET. One starts with an MBE (molecular beam epitaxy)-grown MESFET structure which has an AlAs layer under the GaAs channel layer. Fabrication of the MESFET involves mesa etching, source-drain metallization for nonalloyed contacts, and gate definition. Once the device is completed, one removes the AlAs layer by free etching the device in diluted HF, which selectively etches the AlAs layer. Other epilayers and metals are unaffected by the etchant. The channel is supported by the source and drain metals.