Berlin 2012 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 30: ZnO and Relatives I
HL 30.5: Vortrag
Dienstag, 27. März 2012, 10:30–10:45, EW 202
Photoluminescence studies on zinc oxide surfaces modified with ultrashort pulses — •Andreas Schneider, Kathrin Sebald, and Tobias Voss — Institute of Solid State Physics, University of Bremen, Bremen, Germany
Ultrashort laser pulses can be used to modify the surface morphology of semiconductors resulting in improved properties for applications such as solar cells and photodiodes. Recent studies showed that the modified surface layer can drastically change its absorption characteristics. This is generally attributed to the formation of defects and the transformation of single-crystalline to amorphous and polycrystalline material.
We have applied ultrashort laser pulses to crystalline ZnO wafers in order to change the surface morphology. The influence of variable laser fluences and applied number of laser pulses on the surface structures is identified by scanning electron microscopy. Multi-pulse interaction with the surface layer near its ablation threshold leads to the formation of laser-induced periodic ripples out of the planar sample. In addition, the impact of laser ablation under ambient N2, O2 and medium vacuum atmospheres on the optical properties is studied. The dominant exciton recombination line observed is the donor bound I4 line. Upon varying the laser parameters the peak is broadened and shifted to lower energies. This is accompanied by an overall decrease of the integrated PL intensities. Different line broadening and peak shift mechanisms in the band edge emission must be considered and will be discussed. Finally, the effect of post annealing of fs-laser processed samples on photoluminescence will be presented.