Morphology Control And Photoluminescen-ce Enhancement Of Porous Silicon Nanowires

Recently, much efforts have been devoted to silicon nanowires (Si NWs), owing to the brilliant electrical, mechanical, thermal, and optical properties. For the fabrication of Si NWs, metal-assisted chemical etching is regarded as an ideal one to form uniform porous NW arrays on heavliy doped Si wafers. The optical properties of porous silicon have attracted much attenion since the discovery of its photoluminescence (PL) in1990. Therefore, reasearch on the controllable fabrication and PL enhancement of porous Si NW arrays prepared from metal-assisted chemical etching will be important for semiconductor optoelectronic applications.In this thesis, porous Si NW arrays with controllable morphology and tunable PL were achieved from three types of heavily doped Si wafers. In addition, Si NWs and HfO2material were combined together through atomic layer deposition (ALD), and Si-HfO2core-shell structure was obtained as well as1.7fold PL enhancement. The luminescence qunching of the surface passivated porous Si NWs was also studied by analysing their PL sensing responses with ethanol, and the sensing stability was also remarkably improved.The main results are as follows:(1) Uniform arrays were achieved from heavily doped p-Si-(100), p-Si-(111), and n-Si-(111) wafers, and Si NWs obtained from p-Si-(111) wafers own controllable orientations by tuning the oxidizer concentration in the etchant solution.(2) PL and BET characterization techniques were employed to investigate the effect of oxidizer concentration, substrate orientation, and doping element of the starting Si wafer on Si NWs PL intensity, and their influence mechanism were further studied.(3) Surface passivation was achieved by coating an euphotic layer on the as-prepared Si NWs through ALD. Si-HfO2core-shell structure with1.7fold PL enhancement was obtained, and the explanation for the improved PL as well as a slightly decreased lifetime is presented. Furthermore, the optimization of experimental parameters is studied by changing the euphotic layer material and coating thickness.(4) PL sensor responses with ethanol was performed to investigate the PL quenching of the porous Si NWs arrays, and the sensing stability is strongly improved in terms of surface passivation.