AND CONTROL OF ELECTRIC-FIELD CONFIGURATIONS ALONG MULTIQUANTUM-WELL STRUCTURES

The phenomenon of high-field domain formation and expansion along a su perlattice/multi-quantum well system has been known since the first pi oneering works on these structures. Experimentally it has usually been observed by monitoring negative differential resistance oscillations in the electric characteristics (I-V curves) of the samples. It is due to the fact that a uniform field distribution becomes unstable with r espect to the formation of high and low electric field domains. When i ncreasing the applied field, one can observe the progressive inducemen t of additional quantum well periods into the high-held domain, at vol tages correlated with the alignment energies and with the periods of t he oscillations in the I-V characteristics. Recently, optical tools we re used to probe, in a more direct way, the field distributions along such systems. These experiments can be performed using interband or in tersubband spectroscopies. The behaviour of electric field configurati ons along superlattices/multi-quantum well structures is strongly link ed to the availability of free-space charge. Heavy doping or strong il lumination providing this charge will induce stable field configuratio ns. A supply of charge which is less than needed may result in a spati al oscillation of space charge among different sites. The regime of lo west charge supply can produce transient field domains resulting in sp ontaneous current oscillations reminiscent of transferred electron dev ices and Gunn diodes; however, the negative differential resistance dr iving the effect originates from low-dimensional transport properties rather than from bulk inter-valley transfer. In addition to its import ance for transport studies, the presence of space-charge accumulation at definite sites along a superlattice/multi-quantum well system, toge ther with the presence of different field domains, raise the possibili ty of spatial control, localization and/or modulation of optical nonli near effects along such structures. We review previous studies, which used intersubband spectroscopy to study field domain Switching, and pr esent new results on how to use photoluminescence quenching of interba nd transitions, under the application of an applied field, to further investigate domain formation and expansion in multi-stack samples.