Amplifying planar waveguide structures in Er-doped nanocrystalline II/VI semiconductor layer systems were developed by photolithography and wet chemical etching. 2 μm thick planar waveguides on glass substrates with lateral dimensions down to 5 μm with rectangular cross section were realized. By optical excitation a maximum gain of 82 cm−1 could be determined, which is sufficiently high to allow the design of compact planar amplifiers in this material system. The influence of a thermal sintering step on the gain spectrum and on the fluorescence lifetime has been investigated. By increasing the sintering temperature to 800 °C a consistent increase of gain and fluorescence lifetime was observed.

traps were involved one would expect it to be more efficient in trapping drifting carriers as the concentration goes up. On the other hand, when the Förster transfer is incomplete, each porphyrin molecule is effectively independent of the others and has its own singlet capture range. Since Dexter transfer is not expected to be of larger spatial extent the same is true for capturing triplets, and hence the ratio of the two contributions is independent of the number (concentration) of porphyrin molecules.To conclude, we have provided several experimental results that, when taken together, prove that it is possible to capture the energy from both singlet and triplet excitons and transform it into light emission. This result suggest that it should be possible to make use of 100 % of electron±hole recombination and it lifts the proposed 25 % limit on EL efficiency. Although it is not trivial to find a material combination that will support Dexter transfer as well as Förster transfer, we believe that careful material design will broaden the scope of this technique. We note that even if the porphyrin acts as a recombination center and not as a triplet scavenger, the 25 % limit can still be broken due to the efficient intersystem crossing on the porphyrin. We also showed that we can separate the contributions arising from either singlets or triplets in the host. In order to comment on the ratio between singlets and triplets as generated in the LED, the above result needs to be supplemented only by a measurement of the fraction of triplets that are actually captured by the guest. Another aspect of this work may be that shortening the triplet lifetime in the polymer blend will remove degradation channels associated with the triplet state. [23] Finally, we would like to comment that although the statistical ratio of 3:1 for the ratio of triplets to singlets formed under EL conditions is widely discussed in the literature, there is considerable speculation that there are spin-dependent electron±hole capture processes that lead to a lower ratio in practice. This discussion is driven by recent reports of unexpectedly high LED efficiencies, e.g., 16 lm/W and above in the green part of the spectrum. [24,25] It is hard to measure this ratio experimentally, unless there is direct measurement of the triplet population, for example by excited state absorption. [5] We note that our measurements of triplets through their transfer to the PtOEP provide another route to achieve this. If we assume that all triplet excitons generated in the PNP are captured at PtOEP sites, the 40 % enhancement in triplet emission for EL in contrast to PL (Fig. 4) sets the triplet:singlet production ratio as low as 0.4:1. This is very much a lower limit, since it is unlikely that all triplets are transferred to the PtOEP. Further work is in progress concerning these points.A more complete description of the work by Forrest et al. [10] has recently been published by Baldo et al., [26] showing evidence for triplet±triplet energy transfer in Alq3 and PtOEP bl...

First order gain and index coupled distributed feedback (DFB) gratings were realized in ZnSe-based laser structures using direct implantation with a focused ion beam for gain-modulated structures and conventional electron beam lithography for index modulation. With both technologies, gratings with periods below 90 nm could be achieved, permitting DFB emission in the blue spectral range. Fine tuning of the emission wavelength in steps of 0.14 nm is demonstrated by sampled DFB gratings based on a periodic modulation of the resonator period.

Ar plasma was employed to remove/reduce the oxidation of two typical types of bond pad surfaces, namely aluminum (Al) surface and gold (Au)-coated palladium (Pd) surface, prior to Au wire-bonding process. Field emission scanning electron microscopy (FESEM) and Auger electron spectroscopy (AES) were employed to characterize the bond pad surfaces without and with the plasma cleaning. Processability and reliability results were compared, analyzed and discussed. Although the plasma cleaning did not make significant change for either the Al bond pad surface or the Au-coated Pd bond pad surface in terms of surface morphology, it was found that the impacts of the plasma cleaning on the two types of bond pad surfaces were quite different. On the one hand, for the Al bond pad surface, the Al oxide layer on the bond pad was reduced with the plasma cleaning. However, there was no further significant improvement observed in terms of either the ball shear modes or shear values after wire-bonding process and after stress. On the other hand, for the Au-coated Pd bond pad surface, poor bondability and serious non-stick-on-pad (NSOP) were observed in the initial stage without the plasma cleaning. Its bondability has been improved significantly after the plasma cleaning. Both the shear modes and shear values after the wire-bonding process showed significant improvements for the samples with the plasma cleaning. This is mainly because there was an interdiffusion between the Pd and Au layers; the Pd diffused from underneath to the top of bond pad surface and formed Pd oxide, which degraded the bondability of the bond pad. The plasma cleaning improved the top layer surface condition of the Au-coated Pd bond pad by removing/reducing the Pd oxide.