Electric field profiling in 2D semiconductors exhibiting electrical instabilities

Two novel techniques-field contrast with a scanning electron microscope and electro-optic probing-have been employed to image the formation, and the resulting transients, of high-field domains in GaAs/AlxGa 1-xAs quantum wells. The field contrast mode of a scanning electron microscope involves the analysis of the energy of secondary electrons emitted from the surface of the specimen, the energies of which depend on the local electrostatic fields present at or near the surface, whilst the electro-optic probing technique makes use of the electric-field-induced birefringence that occurs in non-centrosymmetric crystals, such as GaAs. Both techniques are therefore sensitive to changes in the local electric fields within the samples. In this work both techniques were used to profile the electric field distribution along the GaAs quantum well samples where negative differential resistance, and the associated current instabilities, have been induced at room temperature. Unlike the case of bulk material, where high-field domains propagate along the samples (Gunn domains), in 2D GaAs the high-field domains are found to be either static or annihilate before reaching the anode. A model based on a lateral dissipative mechanism is proposed and the merits of the two experimental techniques are discussed in terms of time and spatial resolution.