Parameter space mapping of InAs nanowire crystal structure
TEM images showing crystal structure variations in InAs nanowires. (a) Predominantly ZB nanowire with WZ inclusions of several nanometer long. The c-plane proportion for this nanowire is 0.8. (b) Predominantly ZB nanowire with a high density of individual twin planes. The c-plane proportion for this nanowire is 0.8. (c) Nanowire containing a mixture of ZB and WZ phases with randomly distributed stacking faults and twin planes. The c-plane proportion is close to 0.5. (d) Pure ZB nanowire with c-plane proportion of 1, with the exception of a single WZ segment near the top interface (“neck region”). (e) Predominantly ZB nanowire containing twin planes, arranged in pairs such that there is a favored twin segment orientation. The c-plane proportion is 0.97.
(Color online) Proportion of ZB phase (counted as proportion of c-planes) vs nanowire diameter for different growth temperatures, at a V/III ratio of 100 and 130 , and TMI molar fraction of . Lines are guides for the eye. For all temperatures, there appears to be a transition from WZ to ZB with increasing diameter, such that there is a characteristic transition diameter for each temperature. In the temperature range of , the transition diameter decreases with temperature, but for temperatures below , the transition is shifted to a much lower temperature (such that no transition is visible for within the investigated diameter range).
(Color online) Proportion of ZB phase vs nanowire diameter for growth temperature of and TMI molar fraction of , at V/III ratios of 20 and 100 (90–110 plotted together). There is a clear difference in the dependence, with ZB proportion increasing with diameter at high V/III, but decreasing with diameter at low V/III.
(Color online) Proportion of ZB phase vs growth temperature for nanowires grown with TMI molar fraction of and V/III ratios of 30 and 100. All nanowires have a diameter of . There is a sharp transition from predominantly ZB to predominantly WZ phase at a temperature around . Above this temperature, the proportion of ZB decreases slowly. The transition is sharper for higher V/III ratio.
TEM images illustrating the effect of V/III ratio on InAs nanowire crystal structure at different temperatures. (a) Predominantly WZ nanowires grown at , TMI of , V/III of 30, diameter of 38 nm, and ZB proportion of 0.28. (b) Pure ZB nanowires grown at , TMI of , V/III of 100, diameter of 45 nm, and ZB proportion of 1. (c) ZB nanowires with frequent twin planes grown at , TMI of , V/III of 20, diameter of 35 nm, and ZB proportion of 0.68. (d) Pure WZ nanowires grown at , TMI of , V/III of 100, diameter of 33 nm, and ZB proportion of 0. (e) Pure WZ nanowires grown at , TMI of , V/III of 23, diameter of 41 nm, and ZB proportion of 0. (e) WZ nanowires with frequent stacking faults grown at , TMI of , V/III of 46, diameter of 39 nm, and ZB proportion of 0.12.
TEM images illustrating the effect of precursor mass flow on InAs nanowire crystal structure for selected V/III ratios; TMI flows indicated on the images are . Nanowires are grown at . (a) Pure ZB nanowire grown at V/III of 120, TMI of , and diameter of 58 nm. (b) ZB nanowire with WZ segment inclusions of several nm in length, grown at V/III of 120, TMI of , and diameter of 61 nm. (c) ZB nanowire with frequent twin planes grown at V/III of 30 and TMI of . (d) WZ nanowire with occasional stacking faults grown at V/III of 30 and TMI of .
Images illustrating the effect of precursor mass flow on InAs nanowire growth at a growth temperature of and V/III ratio of 44. The precursor flows are for and for multiplied by factors of (a) 1, (b) 2, (c) 3, and (d) 4. The insets of (a)–(d) are TEM images illustrating the crystal structure for each of the conditions. It is clear that the growth rate and lateral overgrowth scale with the precursor mass flow, but any effect on the crystal structure is minimal.
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