n-i-p-i Doping Superlattices Under High Magnetic Fields

It is well known, that the spatial separation between electrons and holes in doping superlattices results in quite remarkable pecularities of the electronic structure and the electrical and optical properties of semiconductors belonging to this class of materials /1,2/. Due to a strongly reduced overlap between electron and hole wave functions the recombination lifetimes may be enhanced by orders of magnitude compared with the uniform bulk material. Large deviations of the electron and hole concentrations in the n- and p-layers are metastable. The effective bandgap and also the energetic separation between the electric subbands become dynamically tunable. This tuning can be achieved by changing the carrier densities either by optical excitation or by carrier injection or extraction by means of selective n- and p-contacts /3,4/. Another important aspect when dealing with n-i-p-i doping super-lattices is the role of impurities causing bound electronic states and, because of their random distribution, spatial potential fluctuations /1/. Although, in many cases, the impurities lead to undesired broadening of the energy levels, they can also lead to interesting properties, including metal-insulator transitions, in systems of appropriate design as pointed out in a recent paper /4/.