Hydrogen Passivation Kinetics of Si Nanocrystals in SiO 2
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Hydrogen Passivation Kinetics of Si Nanocrystals in SiO2 Andrew R. Wilkinson and Robert G. Elliman Electronic Materials Engineering, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, ACT, 0200
ABSTRACT Hydrogen passivation of non-radiative defects increases the luminescence intensity from silicon nanocrystals. In this study, photoluminescence (PL) and time-resolved PL were used to investigate the chemical kinetics of the hydrogen passivation process. Isochronal and isothermal annealing sequences were used to determine the reaction kinetics for the absorption and desorption of hydrogen, using the generalised consistent simple thermal (GST) model proposed by Stesmans for Pb defects at planar Si/SiO2 interfaces. This included determination of the activation energies and rate constants for the forward and reverse reactions as well as the associated spread in activation energies. The reaction kinetics determined from such measurements were found to be in excellent agreement with those for the passivation of Pb defects at planar Si/SiO2 interfaces, suggesting the nanocrystal emission process is also limited by such defects. These results provide useful model data as well as insight into the processing conditions needed to achieve optimum passivation in H2. As an extension to the work, a preliminary study into passivation by atomic hydrogen was pursued via a post-metallization Al anneal (alneal). A considerable gain in luminescence efficiency was achieved over the previously optimised passivation in H2. INTRODUCTION Si/SiO2 interfacial defects can act as charge traps and consequently degrade the performance of metal-oxide-semiconductor (MOS) devices. The minimization of such defects is therefore a critical step in MOS device fabrication. Hydrogen participates in the passivation of electrically active defects, such as Pb-type defects (.Si ≡ Si3), which are known to be a major source of charge trapping at the Si/SiO2 interface. These particular defects have been studied in detail by electron-spin resonance (ESR) and electrical methods [1], though ESR is typically used to detect these paramagnetic defects. Work by Brower [2, 3] and recent studies by Stesmans [47] have brought insight to the underlying kinetics of this process for planar interfaces. At the (111) Si/SiO2 interface, only one type of defect is observed by ESR, known as the Pb center, whereas the technologically dominant (100) Si/SiO2 contains Pb0 and Pb1 variants. The Pb0 defect is always encountered, whereas the appearance of the Pb1 defect appears to require a minimum level of thermal interfacial relaxation. Studies suggest that the Pb and Pb0 variants are chemically identical and both have been identified as electrical interface traps [7]. Si nanocrystals embedded in SiO2 exhibit strong room-temperature luminescence as a direct consequence of their small size. They are generally fabricated by the precipitation of excess Si in silicon-rich oxides (SRO), where the latter are produced either during deposi
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