Hydrogen-plasma-induced defects

It is known that hydrogen incorporated into Si subsequently exposed to ionizing radiation inhibits the formation of induced secondary point defect (Pearton and Tavendale, 1982a). For example, in both Si and Ge a number of electron or y irradiation induced defect states appear to be vacancy-related, and exposure of the Si or Ge to a hydrogen plasma (or implantation of hydrogen into the sample) prior to irradiation induces a degree of... 

Essential to the identification of H-induced defects in silicon was the use of a remote hydrogen plasma system as described in Section 1.2. The alternative of direct immersion in a plasma introduces charged-particle bombardment and possible photochemical effects that can obscure the purely chemical consequences of hydrogen migrating into silicon. While the evidence presented below strongly argues for the existence of H-induced defects, many issues remain to be resolved. 

In addition to the generation of platelets, hydrogenation of silicon also induces electronic deep levels in the band gap. As in the case of platelet formation, these defects are considered to be unrelated to either plasma or radiation damage because they can be introduced with a remote hydrogen plasma. Comparison of depth distributions and annealing kinetics of the platelets and gap states has been used to a limited extent to probe the relationship among these manifestations of H-induced defects. 

The passivation of two deep-level electron traps induced in n-type Ge by a Q-switched ruby laser anneal was found [141]. As with the corresponding case in Si, plasma exposures of 10 minutes at 100 C were sufficient to neutralize the electrical activity of such centers. In Ge most radiation damage or quenched-in centers that have been found are vacancy-related, and again the propensity of hydrogen to neutralize this type of defect is seen by the effectiveness of hydrogen plasma exposures in passivating Co-60 Y-induced hole traps [142], quenched-in acceptors [143], and ion-implanted oxygen-related deep levels [144]. 

Fig. 11. (a) Capacitance transient spectra from Co-60 - irradiated, n-type Si samples, one of which had been pretreated in an H plasma. Note the reduced defect state density in this sample, (b) Concentration profile of the O-V centers induced in these samples. There is a reduced defect concentration only in the region in which atomic hydrogen was incorporated. 

A number of the well-known radiation-induced centers in silicon, which are known to involve broken bonds, are also neutralized by atomic hydrogen. For exanple, the A-center (oxygen+vacancy coitplex, -0.18 eV), and divacancy level (E -0.23 eV) may be passivated [65]. Point defects produced by the Q-switched ruby-laser-annealing of both n-type [66] and p-type [67] Si surfaces are neutralized to the melt depth of - 1 /mi by plasma exposures of just 10 minutes at 100°C. And there has been a lot of work on the passivation of the electrical activity associated with dislocations (and their attendant point defects) and grain boundaries [66-76], which is so helpful in making photovoltaic solar cells from polycrystalline materials. While these defects may involve broken bonds, it should be remembered that these... 

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