Ga crystallization dynamics during annealing of self-assisted GaAs nanowires

Scarpellini, D.; Fedorov, Alexey; Somaschini, Claudio; Frigeri, C.; Bollani, Monica; Bietti, Sergio; Nöetzel, Richard; Sanguinetti, S.

doi:10.1088/1361-6528/28/4/045605

Cited by 11 publications

(20 citation statements)

References 38 publications

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“…This effect may be minimised through the use of optimised droplet consumption protocols. 8,[21][22][23] In summary, we have examined the defects seen in semiconductor NWs when growth is less than perfect. We use a Burgers circuit protocol that can be applied to high-resolution electron micrographs of multiply twinned material without the problems or ambiguity that affect other approaches.…”

Section: Discussionmentioning

confidence: 99%

Stable Defects in Semiconductor Nanowires

et al. 2018

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Semiconductor nanowires are commonly described as being defect-free due to their ability to expel mobile defects with long-range strain fields. Here, we describe previously undiscovered topologically protected line defects with null Burgers vector that, unlike dislocations, are stable in nanoscale crystals. We analyze the defects present in semiconductor nanowires in regions of imperfect crystal growth, i.e., at the nanowire tip formed during consumption of the droplet in self-catalyzed vapor-liquid-solid growth and subsequent vapor-solid shell growth. We use a form of the Burgers circuit method that can be applied to multiply twinned material without difficulty. Our observations show that the nanowire microstructure is very different from bulk material, with line defects either (a) trapped by locks or other defects, (b) arranged as dipoles or groups with a zero total Burgers vector, or (c) have a zero Burgers vector. We find two new line defects with a null Burgers vector, formed from the combination of partial dislocations in twinned material. The most common defect is the three-monolayer high twin facet with a zero Burgers vector. Studies of individual nanowires using cathodoluminescence show that optical emission is quenched in defective regions, showing that they act as strong nonradiative recombination centers.

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Section: Discussionmentioning

confidence: 99%

Stable Defects in Semiconductor Nanowires

et al. 2018

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“…The final removal of the resist is carried out by 10 min of acetone and isopropanol cleaning; this wet-chemical step may leave resist residues which are therefore removed by a 225 W oxygen plasma and an HF rinse (5% vol) for five seconds prior to loading the sample to the molecular beam epitaxy (MBE) chamber [23]. The SiO 2 /Ge patterned samples undergo a degas step in the MBE chamber at 620 • C for 10 min to ensure a contamination-free surface [24] and then the GaAs is grown (Figure 1c). Several MBE depositions have been carried out by varying the growth rate, the deposition time, the As pressure, and the temperature in order to identify the optimal parameters to achieve selectivity.…”

Section: Methodsmentioning

confidence: 99%

Selective Area Epitaxy of GaAs/Ge/Si Nanomembranes: A Morphological Study

et al. 2020

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We demonstrate the feasibility of growing GaAs nanomembranes on a plastically-relaxed Ge layer deposited on Si (111) by exploiting selective area epitaxy in MBE. Our results are compared to the case of the GaAs homoepitaxy to highlight the criticalities arising by switching to heteroepitaxy. We found that the nanomembranes evolution strongly depends on the chosen growth parameters as well as mask pattern. The selectivity of III-V material with respect to the SiO2 mask can be obtained when the lifetime of Ga adatoms on SiO2 is reduced, so that the diffusion length of adsorbed Ga is high enough to drive the Ga adatoms towards the etched slits. The best condition for a heteroepitaxial selective area epitaxy is obtained using a growth rate equal to 0.3 ML/s of GaAs, with a As BEP pressure of about 2.5 × 10−6 torr and a temperature of 600 °C.

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“…Whereas NW growth models commonly take into account the surface diffusion of group III atoms, 35,36 that of the volatile group V species is usually neglected. 12,13,16,19,37 Several authors nevertheless discuss it 24,38 and some even estimated As diffusion lengths up to hundreds of nm at usual growth temperatures. 39 To obtain the phosphorous diffusion current (iii), we introduce a surface diffusion length λ V and simply assume that all atoms impinging the sidewalls within a distance λ V below the TPL are transferred to the droplet.…”

Section: Direct Group V Impingementmentioning

confidence: 99%

“…Various ex situ observations had previously showed a tapered section near the top of the NW associated with a group-V-rich regime and a flat top facet after total droplet consumption, 12,13,42,43 although others did not detect tapering. 37 On this basis, we solve numerically Eq. ( 7) using the MATLAB environment, with a time step of 0.01 s. At each step k, the four currents contributing to droplet consumption are calculated by using our analytical expressions, evaluated for the instantaneous droplet geometry, defined by parameters β(k), R d (k).…”

Section: Computation Of Droplet Dynamicsmentioning

confidence: 99%

Dynamics of Droplet Consumption in Vapor–Liquid–Solid III–V Nanowire Growth

Pishchagin

Patriarche

Cattoni

et al. 2021

Crystal Growth & Design

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We study experimentally and theoretically the consumption of the apical gallium droplet that mediates the self-catalyzed vapor-liquid-solid growth of GaP nanowires. Consumption is achieved after growth by providing only phosphorous and its progress is monitored ex situ in nanowire arrays fabricated by molecular beam epitaxy. We develop detailed calculations of the process, taking into account four channels of liquid gallium consumption. These include the formation of GaP using phosphorous delivered to the droplet by direct impingement or after re-emission from the substrate. We show that two other channels contribute significantly, namely the diffusion of phosphorous along the sidewalls and gallium back diffusion from the droplet. All currents are calculated analytically as a function of droplet geometry. Complementary experiments are performed to extract the two model parameters governing the diffusion currents. We then compute numerically the dynamics of the system exposed to a constant external phosphorous flux. Our quantitative model allows one to predict how droplet contact angle and radius change while operating blindly in a standard epitaxy chamber. Controlling these parameters is crucial for tailoring the crystal phase of III-V nanowires and fabricating quantum size structures.

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Ga crystallization dynamics during annealing of self-assisted GaAs nanowires

Cited by 11 publications

References 38 publications

Stable Defects in Semiconductor Nanowires

Stable Defects in Semiconductor Nanowires

Selective Area Epitaxy of GaAs/Ge/Si Nanomembranes: A Morphological Study

Dynamics of Droplet Consumption in Vapor–Liquid–Solid III–V Nanowire Growth

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