Electrical modulation for THz radiation from a p-i-n photodetector with a superlattice structure

Summary form only given. We made a p-i-n photodetector with a superlattice structure. The superlattice consists of 5 quantum wells of GaAs at the thickness of 0.85 nm and 4 barriers of AlAs at the thickness of 0.45 nm in the i-region. The p- and n-region are made of AlGaAs and are transparent for light from a mode-locked Ti:sapphire laser. To avoid the effect of carriers photo-excited in the substrate, we used an AlAs/AlGaAs Bragg reflector. The electric field in the superlattice changes the absorption spectrum, so we can modulate the THz radiation by changing the bias voltage. The electric field in the superlattice is determined by the built-in potential in the p-n junction and changed by the external bias voltage. The superlattice is located 500 nm below the surface, so the surface potential is negligible in the superlattice. The THz radiation from the superlattice was detected by a free-space electro-optic sampling system.