| Summary: | 碩士 === 國立東華大學 === 光電工程學系 === 103 === Gold nanoparticles have been used in n-type bulk germanium photodetectors to increase the responsivity. In our study, gold nanoparticles with negative charge, specific modification molecule and coverage ratio of 30-35% has large photo response. In order to verify the previous model of “barrier thinning effect caused by photo-generated holes attracted by gold nanoparticles with negative charges”, we prepare gold nanoparticle with positive charge to compare with the results from the negative charge. We find that positive charge also causes large photo-response. Therefore, we propose a new model of “nano-size distribution of reduced depletion region cause the enhancement of the responsivity”. We measure the C-V value and replace gold nanoparticles by silver nanoparticles to verify this model. After those experiments, we confirm the accuracy of this new model.
Smart-cut can effectively reduce the thickness of the active layer. We try lots of annealing parameters to find out the best parameter for film transferring, and make photodetectors using the thin-film Ge. Because the as-cut detectors can not have obvious difference between photo-currents and dark currents, we turn to etch the elements to reduce the surface roughness and make the surface smoother. Photodetectors with the temperature parameter of 300℃2hr+500℃10min owns the responsivities of 407(no etch), 66(etch 3s) and 183(etch 6s)mA/W. Responsivity of the thin-film Ge detector can compete with the bulk Ge as long as the thickness of remaining Ge is thick enough.
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