TERAHERTZ RADIATION FROM DELTA-DOPED GAAS

Terahertz pulse emission from four different delta-doped molecular bea m epitaxially grown GaAs samples is studied. We observe a decrease of the emitted THz pulse amplitude as the distance of the delta-doped lay er from the surface is increased, and a change in polarity of the THz pulses as compared to bulk n-type doped GaAs reference samples. The el ectric fields in the region of the doping layer are investigated by ph otoreflectance spectroscopy. A careful analysis of Franz-Keldysh oscil lations observed in the photoreflectance spectra provides information about the built-in fields on both sides of the delta-doped layer.