In this paper we discuss the room-temperature modulation properties of terahertz modulators, which depend on the depletion of a two-dimensional electron gas. By changing the electron density of the two-dimensional electron gas in a AlGaAs/GaAs heterostructure by applying an external gate voltage, the transmission and reflection properties of the device change. We studied the modulation properties of different modulator designs using terahertz time-domain spectroscopy and reported a detailed analysis of the electronic properties. We found that the nonideal depletion properties of terahertz modulators can be attributed to an incomplete depletion at low voltages underneath the center of large gates.

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