Radiative Lifetimes of Single Excitons in Semiconductor Quantum Dots- Manifestation of the Spatial Coherence Effect

Using time correlated single photon counting combined with temperature dependent diffraction limited confocal photoluminescence spectroscopy we accurately determine, for the first time, the intrinsic radiative lifetime of single excitons confined within semiconductor quantum dots. Their lifetime is one (two) orders of magnitude longer than the intrinsic radiative lifetime of single excitons confined in semiconductor quantum wires (wells) of comparable confining dimensions. We quantitatively explain this long radiative time in terms of the reduced spatial coherence between the confined exciton dipole moment and the radiation electromagnetic field.Comment: 4 pages, 3 figure

Transmission electron microscopy based interface analysis of the origin of the variation in surface recombination of silicon for different surface preparation methods and passivation materials

In this work, the root cause of variation in surface recombination for Si wafers after different cleaning processes and for different passivation layers is investigated using a combination of calibrated photoluminescence (PL) imaging and transmission electron microscopy (TEM). The use of a HF-last or oxide-last cleaning and/or conditioning process is shown to have a strong impact on surface recombination for SiNx passivated surfaces, but little impact for Al2O3/SiNx stacks. For a SiNx passivation layer, cross-sectional TEM imaging revealed the formation of a â1-2nm SiOx interlayer resulting from a controlled oxidation during the last cleaning/conditioning step. The presence of the SiOx layer reduces the interface defect density (Dit,midgap) by an order of magnitude and dramatically increases the effective carrier lifetime. However, for Al2O3/SiNx passivated surfaces, TEM studies revealed that a SiOx layer is formed at the interface between the c-Si and AlOx even for c leaning processes ending with HF-last treatment due to which the cleaning sequence has minimal impact on the effective carrier lifetime

Pareto Analysis Of Critical Challenges For Emerging Manufacturing Technologies In Silicon Photovoltaics

This work presents the results of a Pareto analysis of critical challenges for emerging manufacturing technologies in c-Si photovoltaics. By soliciting input from members of the PV R&D community, these challenges have been prioritized for six different sub-categories, the first three associated with Processing Challenges and the following three in the area of Metrology Challenges: (1) Feedstock, Crystallization and Wafering; (2) Cell Materials and Processing; (3) Module Integration; (4) Materials and Device Characterization; (5) Reliability and Durability (Measurements); and (6) Modeling and Simulation. Some sub-categories feature a large differential in scoring from the top challenge(s) to lower scored challenges (e.g. Module Integration, Modeling and Simulation), indicating topics of high interest. Other sub-categories feature a more evenly distributed level of prioritization (e.g. Cell Materials and Processing), indicating many high priority challenges within the same area. In total, 14 top critical challenges were identified for the six sub-categories, and a brief review for each of these is provided. As industry and academia seek R&D topics to help push for higher efficiencies and lower cost c-Si modules, this Pareto analysis can hopefully provide some objective insight into areas of high interest for the general PV community. © 2014 Elsevier Ltd