The passivation of nitrogen by hydrogen in dilute nitride semiconductors or dilute nitrides (such as, GaAsN, GaPN and InAsN) is a powerful tool to tailor the electronic and lattice properties of this peculiar class of semiconductors. Dilute nitrides indeed feature great potential in various applicative fields, ranging from telecommunications, to photovoltaics to gas sensing. In this project, we aim at studying a surprising effect by virtue of which the H-induced electronic passivation of N atoms in dilute nitrides depends on the N atom lattice nearest neighbours. In particular, we will investigate this phenomenon in GaAsN, InAsN, and in the intermediate case represented by the InGaAsN alloy. Photoluminescence measurements already performed and being performed will be compared with first-principle supercell calculations to address the physical mechanism responsible for the lack of N passivation by H, whenever N is surrounded by In instead of As. This finding will be finally exploited to create on purpose In-rich regions by laser annealing, thus providing a further tool to modify on demand the electronic properties of dilute nitrides.
These studies are of outmost relevance for the fabrication of nanostructures based on the effects of H in InGaAsN/GaAs QWs. These latter indeed emit photons, whose wavelength is at the first optical window of optical fibres (1.31 micron) [14]. Therefore, passivation of N in this material system will permit to create quantum emitters working at the telecom wavelengths. The number of such sources in the international panorama is very limited and it has been obtained in bottom-up quantum dots (QDs), whose formation is based on a spontaneous random mechanism, whereby QDs form in order to minimize the elastic energy accumulated in in In-rich (In concentration > 50%) InGaAs layers deposited on GaAs [23]. In fact, the large lattice mismatch between InGaAs and GaAs can be relaxed either by the formation of dislocations (namely, crystal fractures that create line defects, where unpaired bonds may capture free electrons and holes causing detrimental effects on the optical performances of the crystal) or by the formation of three-dimensional islands featuring nanometer-sized dimensions. These islands, referred to as self-assembled QDs, act as artificial atoms with a zero-dimensional density of states. One of the most interesting properties of QDs is their ability to act as sources of single and paired photons that are especially important for quantum optics and quantum computing applications [11,12,13]. Unfortunately, self-assembled QDs can be hardly controlled in size and position. This circumstance makes their full exploitation difficult. Consequently, an alternative approach to fabricate QDs that can be size- and position-controlled is extremely important. Our group pioneered a method [7,8,9] to match the position of QDs formed by spatially selective hydrogenation with the defects of photonic crystal cavities, where the electromagnetic field density is concentrated. In this manner, interesting light-matter coupling phenomena can be conveniently studied. Shifting this fabrication method to the telecom wavelengths would be an extremely important step toward the realization of quantum computing protocols working at photon energies of relevance for the information and communication technology.