Impurity bound-to-unbound terahertz sensors based on beryllium and silicon δ-doped GaAs∕AlAs multiple quantum wells

Beryllium and silicon δ-doped GaAs∕AlAs multiple quantum wells (MQWs) were designed and fabricated for selective sensing of terahertz radiation. Optical characterization of the structures by photoreflectance spectroscopy has indicated a presence of built-in electric fields–from 18 up to 49kV∕cm depending on the structure design–located mainly in the cap and buffer layers, but do not penetrating into the MQWs region. Terahertz sensing under normal incidence via impurity bound-to-unbound transitions is demonstrated in photocurrent experiments within 0.6–4.2THz in silicon-doped MQWs and 3.5–7.3THz range in beryllium-doped MQWs at low temperatures.