Deep Level Transition Spectrum

The dependence of trap B on the sample structure is similar to that of trap A. Our results therefore suggest that, for electron trap reduction, increasing the SiN coverage (e.g. from 5 to 6 min deposition) in a single layer is a more effective approach than adding a second nanonetwork layer with the same SiN coverage (double 5 min SiN nanonetworks). 

---

Figure 6.6 Investigated GaN sample structures with single or double SiNr nanonetworks. The topmost 500 nm GaN Si layers (n 0.5-1 x 1017 cm 3) were deposited later for the deep level transition spectrum (DLTS) measurements. Reproduced from Xie JQ et ah, Applied Physics Letters 90(26) Art. No. 262112. Copyright (2007), with permission from the American Institute of Physics...

The introduction of electronic deep levels is demonstrated in Fig. 9 with low-temperature photoluminescence spectra for n-type (P doped, 8 Cl cm) silicon before (control) and after hydrogenation (Johnson et al., 1987a). The spectrum for the control sample is dominated by luminescence peaks that arise from the well-documented annihilation of donor-bound excitons (Dean et al., 1967). After hydrogenation with a remote hydrogen plasma, the spectrum contains several new transitions with the most prominent peaks at approximately 0.95, 0.98, and 1.03 eV. These transitions identify... 

The ro-vibronic spectrum of molecules and the electronic transitions in atoms are only part of the whole story of transitions used in astronomy. Whenever there is a separation between energy levels within a particular target atom or molecule there is always a photon energy that corresponds to this energy separation and hence a probability of a transition. Astronomy has an additional advantage in that selection rules never completely forbid a transition, they just make it very unlikely. In the laboratory the transition has to occur during the timescale of the experiment, whereas in space the transition has to have occurred within the last 15 Gyr and as such can be almost forbidden. Astronomers have identified exotic transitions deep within molecules or atoms to assist in their identification and we are going to look at some of the important ones, the first of which is the maser. 

The presence of an outer open shell in an atom, even if this shell does not participate in the transitions under consideration, influences the X-ray radiation spectrum. Interaction of the vacancy with the open shell, particularly in the final state when the vacancy is not in a deep shell, splits the levels of the core. Depending on level widths and relative strength of various intra-atomic interactions, this multiplet splitting leads to broadening of diagram lines, their asymmetry, the occurrence of satellites, or splitting of the spectrum into large numbers of lines. 

The unoccupied states in the lanthanides can be reached by transitions from deep or shallow core levels. Following Wendin (1983), deep core levels are states in completely filled main shells, i.e. in the K, L and M levels. Levels in the incompletely filled main shells (N, O) are labelled as shallow core levels (except 5d, which is a valence electron level). The impact of this classification becomes clear by inspection of the strongly different types of absorption spectra, observed upon excitation of M and N core levels (fig. 6c). N,y yand M,y y spectra turn out to be completely different, although the d electrons from the shallow Nw.v levels (4d nf,n >4) reach 4f states as the photoelectrons from deep core Miy y levels (3d - nf,n > 4). Each of the M y y spectra exhibits a set of discrete narrow lines. The N,y y spectra on the other hand are dominated by a broad giant resonance above threshold (cf the strong line in fig. 6c). It exhibits only a weak and extended discrete line spectrum at threshold. 

---