Nonradiative recombination

The internal quantum efficiency of a LED is governed by the relative radiative and nonradiative recombination rates. The total recombination rate,... 

R, for electrons is the sum of the radiative and nonradiative recombination rates, and is given by equation 2 ... 

V.N. Abakumov, V. 1. Perel, I.N. Yassievich, in Nonradiative Recombination in Semiconductors, Norlh-Holland, Amsterdam, 1991, p. 108. 

The temperature dependence of luminescence from the sample irradiated at 1 x 1013 cm-2 with 28Si+ indicates, above —110 K, an activation energy of 90 meV for the competing nonradiative recombination process— this competing process may be the thermal dissociation of geminate pairs or bound excitons at donorlike or acceptorlike centers. The 0.09-eV value of activation energy is consistent with the results of Troxell and Watkins (1979). 

Ion implantation generates many dangling bonds that form centers for nonradiative recombination. These centers decrease the carrier lifetime and compete effectively with radiative transitions. However, after hydrogenation, since hydrogen ties dangling bonds, the luminescence process becomes more efficient. Furthermore, since the 1.0-eV emission is obtained even before hydrogen is introduced, the new radiative center may be formed due to residual hydrogen in the c-Si that combines with the implantation-induced defects. 

Nonradiative recombination, 14 837 Nonreactive additive flame retardants, 11 497... 

Interrelationships of Excited-State Decay Routes. The iLV curves conveniently display the competitive nature of photocurrent and luminescence intensity as excited-state deactivation pathways. Our analysis is limited in the sense that we have obtained absolute numbers for X but have had to content ourselves with relative < > r measurements. We lack measures of nonradiative recombination efficiency (4>nr) although they now appear to be... 

When a semiconductor is illuminated with light of sufficient energy, electrons from the valence band are excited to the conduction band and the hole-electron pair is generated. The relaxation can take several pathways some of which are non-radiative. The radiative transition leads to photoluminescence (Fig. 9.20). This is a solid-state analogue of molecular fluorescence. The nonradiative recombination and radiative transitions are again the two competing processes. 

An interesting approach recently applied to doped nanocrystals is the heterocrystalline core-shell method commonly applied to pure nanocrystals. In a series of papers (102, 103), Mn2+ CdS nanocrystals were synthesized in inverted micelles under conditions very similar to those described above and in Figs. 8, 9, and 13. The poor luminescent properties of the resulting Mn2+ CdS nanocrystals were attributed to nonradiative recombination at unpassivated CdS surface states. From the discussion in Section I and II.C, however, it is likely that a large fraction if not all of the Mn2+ ions resided on the surfaces of these as-prepared nanocrystals as observed for Co2+ (Fig. 9). This interpretation is supported by studies in other laboratories that showed large Mn2+ surface populations in Mn2+ CdS nanocrystals grown by the same inverted micelle approach (63). Nevertheless, growth of a ZnS shell around these Mn2+ CdS nanocrystals led to an approximately ninefold increase in Mn2+ 4T 1 > 6A i... 

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