Silicon nanowire (SiNW)-based solar cells on glass substrates have been fabricated by wet electroless chemical etching (using silver nitrate and hydrofluoric acid) of 2.7 microm multicrystalline p(+)nn(+) doped silicon layers thereby creating the nanowire structure. Low reflectance (<10%, at 300-800 nm) and a strong broadband optical absorption (>90% at 500 nm) have been measured. The highest open-circuit voltage (V(oc)) and short-circuit current density (J(sc)) for AM1.5 illumination were 450 mV and 40 mA/cm(2), respectively at a maximum power conversion efficiency of 4.4%.
High-yield synthesis of germanium nanowires (NWs) and core−shell structures is achieved by the chemical vapor deposition (CVD) of dicyclopentadienyl germanium ([Ge(C5H5)2]). The one-dimensional (1D) nanostructures are formed on an iron substrate following a base-growth model in which an Fe−Ge epilayer functions as a catalytic bed. The wire growth is selective and no catalyst particles are observed at the tip of the NWs, which is contrary to the characteristic feature of a 1D growth based on the vapor−liquid−solid (VLS) mechanism. The diameter and length of the NWs were in the ranges 15−20 nm and 25−40 μm, respectively, as found by high-resolution electron microscopy. Both axial and radial dimensions of the NWs can be controlled by adjusting the precursor feedstock, deposition temperature, and size of alloy nuclei in the Fe−Ge epilayer. High precursor flux produced coaxial heterostructures where single-crystalline Ge cores are covered with an overlayer of nanocrystalline Ge. Single-crystal Ge nanowires exhibit a preferred growth direction [112̄] confirmed by X-ray and electron diffraction patterns. When compared to bulk Ge, the micro-Raman spectra of Ge NWs show a low field shift, probably due to the dimensional confinement. Patterned growth of Ge NWs was achieved by shadow-masking the Fe substrate with a carbon film, which prevents the formation of Fe−Ge nuclei, thereby inhibiting the nanowire growth.
The electrical properties of vertically aligned silicon nanowires doped by ion implantation are studied in this paper by a combination of electron beam-induced current imaging and two terminal current-voltage measurements. By varying the implantation parameters in several process steps, uniform p-and n-doping profiles as well as p-n junctions along the nanowire axis are realized. The effective doping is demonstrated by electron beam-induced current imaging on single nanowires, and current-voltage measurements show their well-defined rectifying behavior.Semiconductor nanowires are expected to play a critical role in future electronic devices and sensors. 1 To make use of their semiconducting properties, doping is an important issue. Nanowires that form an epitaxial interface and thus are vertically aligned to the substrate are commonly grown by the vapor-liquid-solid (VLS) mechanism in which a metal catalyst forms eutectic droplets at the growing tips of the nanowires. 2 For silicon nanowires, a supply of Si vapor supersaturates these droplets with Si and leads to its precipitation at the liquid-solid (droplet-silicon) interface. Under the gold droplet, the nanowire grows as long as the Si vapor is present. Silicon nanowires reveal p-type conductance when they are grown using the VLS process without adding any dopant on purpose, but the resistivity is rather high (2 Ω cm 3 -400 Ω cm 4 ).Doping can be realized during the gas phase deposition process by adding dopants to the gas mixture in use for the nanowire growth. Dopant incorporation is reported for diborane, 4 trimethylboron, 5 phosphine, 3 and arsenic. 6 By changing the dopant source during growth, p-n junctions can be realized along the axis of the nanowire. 6,7 Little is known on the dopant incorporation mechanism, however. Therefore, it is not obvious to predict the doping concentration for a given process. Also, recent experimental results reveal the growth of a highly doped shell around the nanowire while doping during VLS growth. 8 As an alternative, reproducible and successful doping of nanowires can be achieved via ion implantation. This technique is a standard doping technique in top-down semiconductor manufacturing and offers the advantage to provide for precise control over the total dose of dopants, depth profile, and most importantly works well also for high doping levels of the order of 10 20 -10 21 cm -3 . It has been demonstrated that GaAs can be p-type doped using Zn ions, and Si by the respective use of B and P ions. 10 The latter work presents field effect transistors based on ion-implanted nanowires. However, the demonstration of ion-implanted nanowires acting as devices by themselves is still lacking. Masking selected parts of the sample at different implantation steps, the doping profile can be chosen to be different from nanowire to nanowire. This is an additional advantage over doping during growth, or etching nanowires out of a doped wafer, as for both these methods all nanowires reveal the same doping concentration. This pap...
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