Silicon surface passivation by silicon nitride deposition

Silicon nitride deposition was studied as a method of passivation for silicon solar cell surfaces. The following three objectives were the thrust of the research: (1) the use of pecvd silicon nitride for passivation of silicon surfaces; (2) measurement techniques for surface recombination velocity; and (3) the importance of surface passivation to high efficiency solar cells

Sub-2 cm/s passivation of silicon surfaces by aprotic solutions

Minimizing recombination at semiconductor surfaces is required for the accurate determination of the bulk carrier lifetime. Proton donors, such as hydrofluoric acid and superacids, are well known to provide highly effective short-term surface passivation. We demonstrate here that aprotic solutions based on bis(trifluoromethanesulfonyl)methane (TFSM) in hexane or pentane can also result in excellent passivation of (100)-orientation silicon surfaces. We show that the optimized TFSM-pentane passivation scheme can measure effective lifetimes up to 20 ms, with a surface recombination velocity of 1.7 cm s1 at an excess carrier density of 1015 cm3 . Fitting injection-dependent lifetime curves requires chemical passivation and field effect passivation from a negatively charged layer with a charge density of 1010–1011 q cm2 . The slightly higher recombination velocity of 2.3 cm s1 measured with TFSM-hexane can be explained by a lower charge density in the passivating layer, suggesting that the steric hindrance associated with the solvent size could play a role in the passivation mechanism. Finally, phosphorus nuclear magnetic resonance experiments confirm that TFSM-based solutions have Lewis acidity without being superacids, which opens up opportunities for them to be used in materials systems sensitive to superacidic environments

Corrosion behaviour of brazing material AA4343

This paper is part of a work devoted to corrosion of brazed AA4343/AA3003/AA4343 materials on water side of automotive heater cores. The microstructure of the superficial resolidified AA4343 brazing material has been previously characterised [1] and [2]. It is composed of large (Al) grains separated by valleys containing multiphase deposits of (Al), Si and α-Al(Mn,Fe)Si. The present study focuses on its electrochemical behaviours in neutral water–ethylene glycol mixtures at different temperatures with and without chloride ions. Three types of behaviour are revealed: (i) passivation, (ii) defective passivation and (iii) pitting corrosion at the corrosion potential. The defective passivation is investigated in greater depth. The results show that Si needles do not participate in the corrosion progress whereas the α-Al(Mn,Fe)Si particles are preferential sites for corrosion attacks. α-Al(Mn,Fe)Si particle/matrix interactions are responsible of the defective passivation at valleys level where the α-Al(Mn,Fe)Si phase particles are mainly concentrated. Increasing the temperature enhances this reactivity whereas addition of ethylene glycol decreases it and favours a transition from defective passivation to passivation for ethylene glycol content higher than 55%

Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs

The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy measurements, coupled with Monte Carlo simulations of THz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump THz-probe spectroscopy, and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, we have demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch THz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast THz photonic devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter

Tuning the thermal conductivity of graphene nanoribbons by edge passivation and isotope engineering: a molecular dynamics study

Using classical molecular dynamics simulation, we have studied the effect of edge-passivation by hydrogen (H-passivation) and isotope mixture (with random or supperlattice distributions) on the thermal conductivity of rectangular graphene nanoribbons (GNRs) (of several nanometers in size). We found that the thermal conductivity is considerably reduced by the edge H-passivation. We also find that the isotope mixing can reduce the thermal conductivities, with the supperlattice distribution giving rise to more reduction than the random distribution. These results can be useful in nanoscale engineering of thermal transport and heat management using GNRs.Comment: 4 pages, 4 figure