Deep levels definition

The next step is the definition of deep. The choice of quantitative values will again involve some arbitrariness. However, a further complication is that there is at present no universally accepted qualitative criterion. For instance, from the point of view of energy level calculations it is often convenient to define deep states as noneffective-mass-like or as those with a localized potential (see, for example, Bassani and Pastori Parravicini, 1975 Jaros, 1980). However, the disadvantage of this definition of deep is that it includes many isoelectronic states that are very shallow on an energy scale. On the other hand, if one uses an energy criterion, should the states be deep with respect to some fraction of the band gap, with respect to kT, or with respect to some shallow levels In this chapter we shall adopt an energy criterion for deep, and we shall require that our states be deep enough to be important in recombination. The importance of deep levels in recombination under many conditions of practical interest was already realized in the early work of Hall... 

The parameter (v) is the average thermal velocity of an electron, Nc the density of states in the conduction band, g the degeneracy of the deep level, and A x = EQ — ET the electron transition energy. Equation (9) also relates the capture constant to the emission rate because of the definition... 

Deep state experiments measure carrier capture or emission rates, processes that are not sensitive to the microscopic structure (such as chemical composition, symmetry, or spin) of the defect. Therefore, the various techniques for analysis of deep states can at best only show a correlation with a particular impurity when used in conjunction with doping experiments. A definitive, unambiguous assignment is impossible without the aid of other experiments, such as high-resolution absorption or luminescence spectroscopy, or electron paramagnetic resonance (EPR). Unfortunately, these techniques are usually inapplicable to most deep levels. However, when absorption or luminescence lines are detectable and sharp, the symmetry of a defect can be deduced from Zeeman or stress experiments (see, for example, Ozeki et al. 1979b). In certain cases the energy of a transition is sensitive to the isotopic mass of an impurity, and use of isotopically enriched dopants can yield a positive chemical identification of a level. 

From Eqs. (25a) and (25b) we may conclude that the deep levels due to Cr and doping are very close at T = 0, with the Cr perhaps lying a little below, but that the Cr level is definitely below the (EL2) level at room temperature. These conclusions differ from those of Martin et al. (1980b), who quote... 

Water with a salinity of less than 10,000 mg/L is considered to be a potential underground source of drinking water. By regulatory definition, deep-well injection of hazardous waste can occur only in very saline waters or brines. Actual salinities of waters in currently used deep-well injection zones vary greatly.70 Normally, the term brine is used to refer to the natural waters in deep-well injection zones. As noted above, however, this term is not technically correct if TDS levels are less than 35,000 mg/L. 

CDC Case Definition An illness with acute onset of fever >101°F followed by a rash characterized by firm, deep seated vesicles or pustules in the same stage of development without other apparent cause. Clinically consistent cases are those presentations of smallpox that do not meet this classical clinical case definition (1) hemorrhagic type, (2) flat type, and (3) variola sine eruptione. Laboratory criteria for diagnosis is (1) polymerase chain reaction (PCR) identification of variola DNA in a clinical specimen, or (2) isolation of smallpox (variola) virus from a clinical specimen (Level D laboratory only confirmed by variola PCR). 

In the Atlantic, deep water anomalies in 3He were found to be considerably less than in the Pacific, in accord with the conclusions based on total saturation anomalies (Section 4.3), but nevertheless quite definitely present in a characteristic level <5 He = 5% (Jenkins et al., 1972). Albeit at a lower level than in the Pacific, the deep Atlantic 3He excesses also show considerable structure in a detailed study of the western Atlantic, Jenkins, and Clarke (1976) observed a maximum <53He of 13% and identified a localized source in the Gibbs Fracture Zone southwest of Iceland. To the south (at about 30°N), a section across the Mid-Atlantic Ridge shows no perceptible influence of the ridge itself on <53He (Lupton, 1976), a result in marked contrast to the comparable data for the East Pacific Rise (Figure 4.4). 

Taking the different arguments together, it is the author s opinion that the dangling bond model remains the more plausible explanation of the 2.0055 defect. Perhaps within a short time, further studies of the hyperfine interaction or calculations of the defect energy levels, etc. will be able to provide definitive proof one way or the other. In the remainder of this book, for the sake of definiteness, we refer to the 2.0055 ESR spin and the associated deep trap as the dangling bond, recognizing that the interpretation of electrical data involves only the gap state levels and the electron occupancy, not the atomic structure. 

A deep reason for this fanatic belief is the gauge principle. I would say that all empirical conservation laws not protected by the gauge principle are doomed to be violated at some level of strength. The only relevant question is at which energy scales these conservation laws are violated. Both theory and experiment should give definitive signatures for this energy scale. We already seem to have some hint on this. 

Brodkey [56] stated that only with the advent of the modem turbulence theory a deep understanding of micro-mixing processes and turbulent scalar transfer processes on a microscopic level was possible and that this theory enabled the definition of measurable mixing criteria. Knowledge of the turbulence parameter made it possible to estimate the degree of mixing. The parameters could be estimated from the geometry of the flow system and from simple empirical expressions. The... 

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