  This paper is the first report of n-type GaAs as a cryogenic scintillation
radiation detector for the detection of electron recoils from interacting dark
matter (DM) particles in the poorly explored MeV/c2 mass range. Seven GaAs
samples from two commercial suppliers and with different silicon and boron
concentrations were studied for their low temperature optical and scintillation
properties. All samples are n-type even at low temperatures and exhibit
emission between silicon donors and boron acceptors that peaks at 1.33 eV (930
nm). The lowest excitation band peaks at 1.44 eV (860 nm) and the overlap
between the emission and excitation bands is small. The X-ray excited
luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence
measurements show that n-type GaAs does not accumulate metastable radiative
states that could cause afterglow. Further development and use with cryogenic
photodetectors promises a remarkable combination of large target size,
ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that
would be produced by DM particles as light as a few MeV/c2.
