Abstract
We have studied the optical properties and carrier dynamics in SnO2nanowires (NWs) with an average radius of 50 nm that were grown via the vapor–liquid solid method. Transient differential absorption measurements have been employed to investigate the ultrafast relaxation dynamics of photogenerated carriers in the SnO2NWs. Steady state transmission measurements revealed that the band gap of these NWs is 3.77 eV and contains two broad absorption bands. The first is located below the band edge (shallow traps) and the second near the center of the band gap (deep traps). Both of these absorption bands seem to play a crucial role in the relaxation of the photogenerated carriers. Time resolved measurements suggest that the photogenerated carriers take a few picoseconds to move into the shallow trap states whereas they take ~70 ps to move from the shallow to the deep trap states. Furthermore the recombination process of electrons in these trap states with holes in the valence band takes ~2 ns. Auger recombination appears to be important at the highest fluence used in this study (500 μJ/cm2); however, it has negligible effect for fluences below 50 μJ/cm2. The Auger coefficient for the SnO2NWs was estimated to be 7.5 ± 2.5 × 10−31 cm6/s.
Highlights
Tin oxide (SnO2) is considered an important wide-bandgap n-type semiconductor which has received a great deal of attention over the past few years due to its high transparency in the visible part of the spectrum and sensitivity to certain gases which make it technologically important for optoelectronic devices [1,2,3,4,5,6] and sensors [7]
We find that the band gap of the SnO2 NWs is 3.77 eV and contains two broad absorption bands, the first of which is located below the band edge and is related to Nanoscale Res Lett (2009) 4:828–833 shallow trap states while the second is near the center of the band gap due to deep trap states
A typical scanning electron microscope (SEM) image of the SnO2 NWs grown on quartz is shown in Fig. 1 where it is apparent that a large coverage has been obtained
Summary
Tin oxide (SnO2) is considered an important wide-bandgap n-type semiconductor which has received a great deal of attention over the past few years due to its high transparency in the visible part of the spectrum and sensitivity to certain gases which make it technologically important for optoelectronic devices [1,2,3,4,5,6] and sensors [7]. Here we investigate the carrier dynamics in SnO2 NWs and obtain a detailed understanding of the various relaxation mechanisms and the influence of trap states using transient white light absorption spectroscopy [14,15,16] with femtosecond resolution.
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