Sub-Poissonian Narrowing of Length Distributions Realized in Ga-Catalyzed GaAs Nanowires

Abstract

Herein, we present experimental data on the record length uniformity within the ensembles of semiconductor nanowires. The length distributions of Ga-catalyzed GaAs nanowires obtained by cost-effective lithography-free technique on silicon substrates systematically feature a pronounced sub-Poissonian character. For example, nanowires with the mean length ⟨L⟩ of 2480 nm show a length distribution variance of only 367 nm, which is more than twice smaller than the Poisson variance h⟨L⟩ of 808 nm for this mean length (with h = 0.326 nm as the height of GaAs monolayer). For 5125 nm mean length, the measured variance is 1200 nm against 1671 nm for Poisson distribution. A supporting model to explain the experimental findings is proposed. We speculate that the fluctuation-induced broadening of the length distribution is suppressed by nucleation antibunching, the effect which is commonly observed in individual vapor-liquid-solid nanowires but has never been seen for their ensembles. Without kinetic fluctuations, the two remaining effects contributing to the length distribution width are the nucleation randomness for nanowires emerging from the substrate and the shadowing effect on long enough nanowires. This explains an interesting time evolution of the variance that saturates after a short incubation stage but then starts increasing again due to shadowing, remaining, however, smaller than the Poisson value for a sufficiently long time.

Stabilization of the Morphology and Crystal Phase in Ensembles of Self‐Catalyzed GaAs Nanowires

“…Self‐catalyzed vapor–liquid–solid (VLS) growth of III–V nanowires (NWs) is a promising gold‐free method for synthesis of high crystal quality and size‐uniform ensembles of NWs. Most self‐catalyzed III–V NWs are grown by molecular beam epitaxy (MBE) in regular arrays on lithographically patterned SiO x /Si(111) substrates with gallium predeposition, or using other methods of gallium droplet organization . Recently, sub‐Poissonian narrowing of the length distributions has been demonstrated for gallium‐catalyzed GaAs NWs .…”

“…The function is given by and generally depends on , , , , and . The collection length may be limited by the shadowing effect in MBE, with the trivial shadowing length related to the array pitch and the beam angle as . The value of is very large for short NWs due to the additional collection of gallium adatoms from the smooth oxide surface, whereas, for long NWs with , it saturates to the length‐independent value .…”

“…It is shown that all nanowires stabilize to a stationary radius and pure zincblende phase within the optimal range of V/III flux ratios. Lower V/III flux ratios yield pure zincblende phase without any radius stabilization, whereas higher V/III ratios lead to a limited focusing of the radius, polytypism, or even pure wurtzite phase of GaAs nanowires.Self-catalyzed vapor-liquid-solid (VLS) growth of III-V nanowires (NWs) [1][2][3][4][5][6][7][8][9][10][11][12][13] is a promising gold-free method for synthesis of high crystal quality and size-uniform ensembles of NWs. Most self-catalyzed III-V NWs are grown by molecular beam epitaxy (MBE) in regular arrays on lithographically patterned SiO x / Si(111) substrates with gallium predeposition, [4,6,10,13] or using other methods of gallium droplet organization.…”

“…Most self-catalyzed III-V NWs are grown by molecular beam epitaxy (MBE) in regular arrays on lithographically patterned SiO x / Si(111) substrates with gallium predeposition, [4,6,10,13] or using other methods of gallium droplet organization. [11,12] Recently, sub-Poissonian narrowing of the length distributions has been demonstrated for gallium-catalyzed GaAs NWs. [11,12] Selfstabilization of the radius distribution of self-catalyzed III-V NWs has been predicted in the previous studies [8][9][10] and confirmed experimentally for GaAs NWs.…”

“…[11,12] Recently, sub-Poissonian narrowing of the length distributions has been demonstrated for gallium-catalyzed GaAs NWs. [11,12] Selfstabilization of the radius distribution of self-catalyzed III-V NWs has been predicted in the previous studies [8][9][10] and confirmed experimentally for GaAs NWs. [10] However, full narrowing to a delta-like shape is not seen as regularly as it could be expected according to the models given in the previous studies.…”