Thermal Stability of Passivation

IMPURITIES OR DEFECTS IN SI SUSCEPTIBLE TO HYDROGENATION AND THE CORRESPONDING ENERGY LEVELS. Ea DENOTES THE ACTIVATION ENERGY OF REACTIVATION. E AND H REFER TO ELECTRON OR HOLE TRAP RESPECTIVELY. 

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Even if LiPFe is replaced by more thermally stable salts, the thermal stability of passivation films on both the anode and the cathode would still keep the high-temperature limits lower than 90 °C, as do the thermal stability of the separator (<90 °C for polypropylene), the chemical stability of the insulating coatings/sealants used in the cell packaging, and the polymeric binder agents used in both cathode and anode composites. 

In MBE grown GaAs three dominant electron traps are usually observed Ml at c - 0.17 eV, M3 at c - 0.28 eV and M4 at c - 0.45 eV. Exposure of MBE grown material to a hydrogen plasma for 30 minutes at 250°C completely passivates these three deep levels as shown in Fig. 10 (Dautremont-Smith et al., 1986). After five minute anneals at 400°C or 500°C, the passivation remains complete while the shallow donors are fully reactivated. A five minute annealing at 600°C partially restores the electrical activity of M3. Therefore the thermal stability of the neutralization of deep levels in MBE material is much higher than in other materials and is compatible with most technological treatments. 

As far as the passivation of deep level defects by hydrogen is concerned, their understanding is rather poor, partly because the microscopic structure of these deep level centers is largely unknown. The thermal stability of the passivation of these deep centers has the advantage of being usually compatible with the temperature used in the process of III-V devices. This point might already create an interest in the field of applications. 

One of the interests of a spectroscopic study of hydrogenated CZ silicon was a search for electronic spectra associated with partially passivated TDD°s similar to those observed for sulphur in silicon. DLTS measurements have proved the passivation of the electrical activity of TDDs in silicon after exposure to a hydrogen plasma at relatively low temperature (100-150°C) [42,120]. The reduction of the TDDs concentration indicates that in the region closest to the surface, full passivation is achieved. The thermal stability of the (TDD,H) complexes thus created has been found to be moderate, and full electrical recovery takes place at about 200°C. The passivation efficiency depends on the TDDi considered, but this is not discussed here. It has been suggested that some of the STD(H) centers could be H-passivated TDDi [187]. However, the temperature difference between the reactivation of the H-passivated TDDi ( ---200 ( ) and the temperature of dissociation of STD(H) centres (—500°C) has led to abandon this assumption [216]. 

Influence of proton irradiation and hydrogen passivation on the photoluminescence (PL) of MBE grown Ge/Si quantum dots (QDs) has been studied. An enhanced resistance of the QDs against irradiation as compared to the quantum wells and bulk silicon has been found. The passivation improves the thermal stability of the QD luminescence whereas the irradiation reduces it. Various carrier/exciton redistribution processes among the PL centers and the influence of defects have been observed. 

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