Schematic illustration of "modified modulation" doping. (a) QDs dispersed in a stoichiometric SiO2 matrix - dopant atoms cannot be ionised as they create very deep levels. (b) QDs surrounded by an amorphous sub-oxide region between regions of full stoichiometric barrier material - dopant atom levels are shallow enough to be ionised at room temperature and 'modulation' dope the QDs.
Conibeer et al. Nanoscale Research Letters 2012 7:193 doi:10.1186/1556-276X-7-193