We have fabricated GaAs-based microelectromechanical systems' (MEMSs) terahertz bolometers on high-resistivity Si substrates by using a wafer-bonding technique. In contrast to polar GaAs, nonpolar Si has very small absorption in the terahertz (THz) frequency range. The wafer-bonded MEMS bolometers show a large responsivity even in the Reststrahlen band of GaAs, where the responsivity vanishes in the conventional MEMS bolometers fabricated on GaAs substrates. Furthermore, we have observed two peaks in the responsivity spectrum near the TO and LO phonon frequencies of GaAs, which originate from an interplay between strong reflection in the Reststrahlen band and strong absorption at the TO phonon frequency in the GaAs MEMS beam. The present result demonstrates that the wafer-bonded MEMS bolometers are a very good candidate for the room-temperature, fast, and sensitive broadband THz detection.

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