450°C thermal donors

These may include atomic and molecular hydrogen, as well as hydrogen bonded at oxygen-related clusters. Passivation of the 450°C thermal donors has also been investigated as a function of cluster size by Johnson and Hahn (1986) and Johnson et al. (1986). 

Conversion of coal to benzene or hexane soluble form has been shown to consist of a series of very fast reactions followed by slower reactions (2 3). The fast initial reactions have been proposed to involve only the thermal disruption of the coal structure to produce free radical fragments. Solvents which are present interact with these fragments to stabilize them through hydrogen donation. In fact, Wiser showed that there exists a strong similarity between coal pyrolysis and liquefaction (5). Recent studies by Petrakis have shown that suspensions of coals in various solvents when heated to 450°C produce large quantities of free radicals (. 1 molar solutions ) even when subsequently measured at room temperature. The radical concentration was significantly lower in H-donor solvents (Tetralin) then in non-donor solvents (naphthalene) (6). 

Fig. 5. Capacitance and current transient spectra from -type, CZ grown Si annealed for 18h at 450°C to form the shallow, oxygen thermal donors. (Chantre et al., 1987). Hydrogenation at 200°C passivates the electrical activity of these thermal donors (Chantre et at, 1987).

Shallow donors (or acceptors) add new electrons to the CB (or new holes to the VB), resulting in a net increase in the number of a particular type of charge carrier. The implantation of shallow donors or acceptors is performed for this purpose. But this process can also occur unintentionally. For example, the precipitation aroimd 450°C of interstitial oxygen in Si generates a series of shallow double donors called thermal donors. As-grown GaN crystal are always heavily n type, because of some intrinsic shallow-level defect. The presence and type of new charge carriers can be detected by Hall effect measm ements. 

---