ELECTRIC-FIELD PROFILING IN 2D SEMICONDUCTORS EXHIBITING ELECTRICAL INSTABILITIES

Two novel techniques-field contrast with a scanning electron microscop e and electro-optic probing-have been employed to image the formation, and the resulting transients, of high-field domains in GaAs/AlxGa1-xA s quantum wells. The field contrast mode of a scanning electron micros cope involves the analysis of the energy of secondary electrons emitte d from the surface of the specimen, the energies of which depend on th e local electrostatic fields present at or near the surface, whilst th e electro-optic probing technique makes use of the electric-field-indu ced 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 quantu m well samples where negative differential resistance, and the associa ted current instabilities, have been induced at room temperature. Unli ke the case of bulk material, where high-field domains propagate along the samples (Gunn domains), in 2D GaAs the high-field domains are fou nd to be either static or annihilate before reaching the anode. A mode l 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.