Anregungsmechanismus von Er3+ in a-Si:H

The aim of this work is the examination of the optoelektronical material a-Si:H (Er). It is characterised in the good electonic properties of the a-Si:H and the emission wavelength of 1.5 micrometer of erbium which coinsides with the absorbtion minimum of glasfibres. Photolumineszense measurements confirm the assumption that oxigen is necessary for the optical activation of Er3+ in addition to the symmetrical breaking of the crystal field. The flexible lattice of a-Si:H enables a high concentration of Erbium up to 5·10exp21/cm3 with a quantum efficiency of the luminescence of 0.5-1.5·10exp-4 at room temperature. Photoluminescence excitation and absorption measurements of a-Si:H (Er)show, that there is no direct excitation of the erbium ions because the absorption of the Er3+ ions is two orders of magnitude below the absorption of silicon. The excitation or the Er3+ Ions takes place through the absorption in silicon with additional energy transfer to Erbium. Photoluminescence measurements are done in order to differentiate between the possible excitation channels, the intrinsic bond-bond channel and the excitation through defects. The different temperature dependence of the intensity of the intrinsic luminescence (77K-300K >3 orders of magnitude) in comparison with the defect luminescence and the Erbiumluminescence (both 1-1.5 orders of magnitude) shows that the energy transfer takes place over defects. Luminescence and absorption measurements with boron doped a-Si:H (Er) show no dependence of the Erbium luminescence in dependence of defect density or the electrical charge of the defects. The luminescence spectra show a break in the defect luminescence at 0.84eV. This agrees with the first excitated state of the Er3+ ion combined with a clearly smaller line width of the defect luminescence (0.18eV in comparision with >0.3eV in erbium free a-Si.H). This result shows the resonance of the energy transfer. The resonance is assisted through PL measurements at a-Si(1-x)C(x):H (Er) films which show change in energetic Position of defects in dependence of the amount of carbon. Samples of different deposition processes: Sputtering and deposition of an organic molecule with PECVD Process show identical PL intensities even though EXAFS measurements show that a great peace of the organic material is implemented. This suggests a relatively high range of the energy transfer which is a disagreement to the discussed excitation model with Auger excitation. This model requires a special overlap of the wave function of electron, dangling bond and Erbium. The resonant Förster transfer is suggested as excitation transfer. The energy is transported through dipole-dipole interaction with a range of 50Å.