Very fast millimeter wave mixers have been fabricated from a high mobility two-dimensional electron gas (2DEG) in a GaAs-AlGaAs heterostructure. Using a 115 GHz local oscillator, intermediate frequency (IF) bandwidths exceeding 20 GHz have been obtained for channel lengths L of a few microns. Operating at 77 K, the IF bandwidth scales as L~(-2). indicating that the response speed is determined by the diffusion transit time of hot electrons to the leads.
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