Abstract
Periodically ordered arrays of vertically aligned Si nanowires (Si NWs) are successfully fabricated with controllable diameters and lengths. Their photoconductive properties are investigated by photoconductive atomic force microscopy (PCAFM) on individual nanowires. The results show that the photocurrent of Si NWs increases significantly with the laser intensity, indicating that Si NWs have good photoconductance and photoresponse capability. This photoenhanced conductance can be attributed to the photoinduced Schottky barrier change, confirmed by I–V curve analyses. On the other hand, electrostatic force microscopy (EFM) results indicate that a large number of photogenerated charges are trapped in Si NWs under laser irradiation, leading to the lowering of barrier height. Moreover, the size dependence of photoconductive properties is studied on Si NWs with different diameters and lengths. It is found that the increasing magnitude of photocurrent with laser intensity is greatly relevant to the nanowires’ diameter and length. Si NWs with smaller diameters and shorter lengths display better photoconductive properties, which agrees well with the size-dependent barrier height variation induced by photogenerated charges. With optimized diameter and length, great photoelectrical properties are achieved on Si NWs. Overall, in this study the photoelectrical properties of individual Si NWs are systematically investigated by PCAFM and EFM, providing important information for the optimization of nanostructures for practical applications.
Highlights
Silicon nanowires (Si Si nanowires (NWs)) have attracted great attention in recent years due to their unique properties and compatibility with traditional silicon technology
Photoconductive Property Measurements on Single Si NWs By combining with laser irradiation, the photoconductive properties of Si NWs are investigated by photoconductive atomic force microscopy (PCAFM) as a function of laser intensity
The results show that the average current has about two times increase as the laser intensity increases from 0 to 8 W/cm2, indicating more carriers are generated under laser irradiation
Summary
Silicon nanowires (Si NWs) have attracted great attention in recent years due to their unique properties and compatibility with traditional silicon technology. PCAFM has already been employed to photocurrent measurements on organic [23,24,25,26] and inorganic solar cells [27,28,29], as well as on some nanostructures, including microcrystalline Si thin films, CdS heterostructures, MoS2 films and ZnO NWs [30,31,32,33] Most of these studies focused on the influence of laser irradiation with varied power intensities or wavelengths, while a few researches concerned with the effect of nanowires’ size
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