  The authors demonstrate selective detection of terahertz radiation employing
beryllium delta-doped GaAs/AlAs multiple quantum wells. The sensitivity up to 1
V/W within 4.2-7.3 THz range at liquid helium temperatures is reached. The
Franz-Keldysh oscillations observed in photo- and electro-reflectance spectra
allowed one to estimate built-in electric fields in the structures studied. It
was found that the electric field strength in the cap layer region could vary
from 10 kV/cm up to 26 kV/cm, depending on the structure design and
temperature.

Materials Science;Other Condensed Matter