We study the microwave photo-response of a quantum point contact (QPC) formed on a GaAs/AlGaAs heterostructure with a high-electron-mobility two-dimensional electron gas. The QPCs are fabricated by two types of gates: a traditional split gate and a specially designed bridged gate. We observe a three orders of magnitude enhancement of the dark QPC conductance in the tunneling regime at the incident microwave power density of 10 mW/cm2. The response of the bridged-gate structure is more than ten times larger than that of the split-gate QPC. This giant effect and the difference between the two types of gates are explained by the influence of microwaves on the steady-state electron distribution function in the vicinity of the tunnel contact. Experimental results are in good quantitative agreement with theoretical calculations. The bridged-gate QPC can be used for the creation of highly sensitive detectors of electromagnetic radiation.

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