Abstract
Highly faceted geometries such as nanowires are prone to form self-formed features, especially those that are driven by segregation. Understanding these features is important in preventing their formation, understanding their effects on nanowire properties, or engineering them for applications. Single elemental segregation lines that run along the radii of the hexagonal cross-section have been a common observation in alloy semiconductor nanowires. Here, in GaAsP nanowires, two additional P rich bands are formed on either side of the primary band, resulting in a total of three segregation bands in the vicinity of three of the alternating radii. These bands are less intense than the primary band and their formation can be attributed to the inclined nanofacets that form in the vicinity of the vertices. The formation of the secondary bands requires a higher composition of P in the shell, and to be grown under conditions that increase the diffusivity difference between As and P. Furthermore, it is observed that the primary band can split into two narrow and parallel bands. This can take place in all six radii, making the cross sections to have up to a maximum of 18 radial segregation bands. With controlled growth, these features could be exploited to assemble multiple different quantum structures in a new dimension (circumferential direction) within nanowires.
Highlights
Epitaxial growth may deviate from its simple form due to growth rate anisotropy, strain, entropy of mixing in alloys and capillarity, forming unintended self-formed features [1, 2]
Nanowires, which themselves are a result of growth rate anisotropy, are prone to develop such self-formed features due to coexistence of multiple growth facets. Different types of such nanowire features have been reported, including unintentional core–shell structures [3, 4], radial elemental segregations [5,6,7,8,9,10,11,12], alloy fluctuations [13, 14], longitudinal wires that form along the vertical edges [15,16,17] and pyramidical elemental segregations [18, 19]
Dark bands that extend radially towards the corners of the hexagon are visible in both shells. These lines correspond to P rich bands as the contrast in ADF images is related to the atomic number, with lighter elements appearing in dark contrast
Summary
Epitaxial growth may deviate from its simple form due to growth rate anisotropy, strain, entropy of mixing in alloys and capillarity, forming unintended self-formed features [1, 2]. Nanowires, which themselves are a result of growth rate anisotropy, are prone to develop such self-formed features due to coexistence of multiple growth facets Different types of such nanowire features have been reported, including unintentional core–shell structures [3, 4], radial elemental segregations [5,6,7,8,9,10,11,12], alloy fluctuations [13, 14], longitudinal wires that form along the vertical edges [15,16,17] and pyramidical elemental segregations [18, 19]. This knowledge can be used to engineer the regions between the P rich bands to form quantum wells (QWs) along the circumference; a new form of nanowire based quantum structure, that may bear important implications for novel quantum device engineering [23, 24]
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