Nanowires (NWs) with radial p‐i‐n junction have advantages, such as large junction area and small influence from the surface states, which can lead to highly efficient material use and good device quantum efficiency. However, it is difficult to make high‐quality core–shell NW devices, especially single NW devices. Here, the key factors during the growth and fabrication process that influence the quality of single core–shell p‐i‐n NW devices are studied using GaAs(P) NW photovoltaics as an example. By p‐doping and annealing, good ohmic contact is achieved on NWs with a diameter as small as 50–60 nm. Single NW photovoltaics are subsequently developed and a record fill factor of 80.5% is shown. These results bring valuable information for making single NW devices, which can further benefit the development of high‐density integration circuits.

Two-dimensional (2D) metal chalcogenides (MC) such as MoS have been recognized as promising materials for near future applications. However, general strategies to functionalize them are still scarce, while the nature of functionalization still remains unclear. Herein, we demonstrate a simple and universal functionalization route through complexation reaction between the amino-containing organic agents and MCs. Degrees of functionalization are tunable by adjusting the organic group types and ratios. No further defects are introduced and the functionalized 2D MCs are dispersible in corresponding typical solvents. Both experimental results and geometry optimization calculations indicate that the grafting of functional groups through the coordination effect truly exist, while the surface properties and resulting photoelectric properties of 2D MCs are greatly altered. More intriguingly, our proposed functionalization process is demonstrated to be universal and can be applied to different MCs, thus opening new avenues for the application of 2D MCs.

One of the nanowire characteristics is its preferred elongation direction. Here, we investigated the impact of Si substrate crystal orientation on the growth direction of GaAs nanowires. We first studied the selfcatalyzed GaAs nanowire growth on Si (111) and Si (001) substrates. SEM observations show GaAs nanowires on Si (001) are grown along four <111> directions without preference on one or some of them. This non-preferential nanowire growth on Si (001) is morphologically in contrast to the extensively reported vertical <111> preferred GaAs nanowire growth on Si (111) substrates. We propose a model based on the initial condition of an ideal Ga droplet formation on Si substrates and the surface free energy calculation which takes into account the dangling bond surface density for different facets. This model provides further understanding of the different preferences in the growth of GaAs nanowires along selected <111> directions depending on the Si substrate orientation. To verify the prevalence of the model, nanowires were grown on Si (311) substrates. The results are in good agreement with the three-dimensional mapping of surface free energy by our model. This general model can also be applied to predictions of nanowire preferred growth directions by the vapor-liquid-solid growth mode on other group IV and III-V substrates.

Self-catalyzed AlGaAs nanowires (NWs) and NWs with a GaAs quantum dot (QD) were monolithically grown on Si(111) substrates via solid-source molecular beam epitaxy. This growth technique is advantageous in comparison to the previously employed Au-catalyzed approach, as it removes Au contamination issues and renders the structures compatible with complementary metal–oxide–semiconductor (CMOS) technology applications. Structural studies reveal the self-formation of an Al-rich AlGaAs shell, thicker at the NW base and thinning towards the tip, with the opposite behavior observed for the NW core. Wide alloy fluctuations in the shell region are also noticed. AlGaAs NW structures with nominal Al contents of 10, 20, and 30% have strong room temperature photoluminescence, with emission in the range of 1.50–1.72 eV. Individual NWs with an embedded 4.9 nm-thick GaAs region exhibit clear QD behavior, with spatially localized emission, both exciton and biexciton recombination lines, and an exciton line width of 490 μeV at low temperature. Our results demonstrate the properties and behavior of the AlGaAs NWs and AlGaAs/GaAs NWQDs grown via the self-catalyzed approach for the first time and exhibit their potential for a range of novel applications, including nanolasers and single-photon sources.

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