  A fast, voltage-tunable terahertz mixer based on the intersubband transition
of a high-mobility 2-dimensional electron gas (2DEG) has been fabricated from a
single 40 nm GaAs-AlGaAs square quantum well heterostructure. The device is
called a Tunable Antenna-Coupled Intersubband Terahertz (TACIT) mixer, and
shows tunability of the detection frequency from 2.52 THz to 3.11 THz with
small (< 1 V) top gate and back gate voltage biases. Mixing at 2.52 THz has
been observed at 60 K with a -3dB intermediate frequency (IF) bandwidth
exceeding 6 GHz.
