Gate controlled 2-DEG varactor for VCO applications in microwave circuits

A novel gate-controlled Schottky diode varactor is introduced. The three terminal varactor is a modulation doped heterostructure of AlGaAs-GaAs with two Schottky contacts, similar to a metal-semiconductor-metal (MSM) diode. Schottky metal contacts are made to a two dimensional electron gas (2-DEG). The third, gate, contact is formed from highly doped n/sup +/ GaAs material to allow an open optical window that can be used for optical gating and mixing. Structure capacitance is less than 1 pF and a change of more than 30 percent from the zero bias capacitance is observed with the applied gate voltage. The interdigital structure dimensions can be scaled to cover a wide range of operation in the microwave and millimeter wave regimes.