Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multiphonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.
Bibliographical noteFunding Information:
We thank Ritoban Basu Thakur, Alvaro Chavarria, Alan Robinson, and Matt Pyle for useful discussions. YH is supported by the U.S. National Science Foundation under Grant No.PHY-1002399. KZ and TL are supported by the DoE under Contract No.DE-AC02-05CH11231. TL is also supported by NSF Grant No.PHY-1316783.
© 2017 American Physical Society.