Droplet-Confined Alternate Pulsed Epitaxy of GaAs Nanowires on Si Substrates down to CMOS-Compatible Temperatures

Abstract

We introduce droplet-confined alternate pulsed epitaxy for the self-catalyzed growth of GaAs nanowires on Si(111) substrates in the temperature range from 550 °C down to 450 °C. This unconventional growth mode is a modification of the migration-enhanced epitaxy, where alternating pulses of Ga and As4 are employed instead of a continuous supply. The enhancement of the diffusion length of Ga adatoms on the {11̅0} nanowire sidewalls allows for their targeted delivery to the Ga droplets at the top of the nanowires and, thus, for a highly directional growth along the nanowire axis even at temperatures as low as 450 °C. We demonstrate that the axial growth can be simply and abruptly interrupted at any time without the formation of any defects, whereas the growth rate can be controlled with high accuracy down to the monolayer scale, being limited only by the stochastic nature of nucleation. Taking advantage of these unique possibilities, we were able to probe and describe quantitatively the population dynamics of As inside the Ga droplets in specially designed experiments. After all, our growth method combines all necessary elements for precise growth control, in-depth investigation of the growth mechanisms and compatibility with fully processed Si-CMOS substrates.

Measuring and Modeling the Growth Dynamics of Self-Catalyzed GaP Nanowire Arrays

“…In particular, the steady state value of the axial growth rate, 1 nm.s −1 , is similar to what has been reported in self-catalyzed GaAs NW growth studies. 2,15,28 Yet, we find a peculiar situation in which the GaP NWs are not tapered whereas their instantaneous diameter varies significantly during growth. Again, this has been previously observed in GaAs NWs arrays 23 but recent theoretical studies do not consider this phenomenon.…”

Synthesis and Applications of III–V Nanowires

“…MBE is so far the most commonly used growth technique for self-seeded NWs although MOVPE has been used to some extent. Recently, the materials grown by the self-seeded technique using Ga seed particles includes GaAs, ,− GaP, , GaAsP, − and GaAs 1 Sb 1– x , , while In seed particles have been used to grow InAs and InP. − …”

Radial Growth of Self-Catalyzed GaAs Nanowires and the Evolution of the Liquid Ga-Droplet Studied by Time-Resolved in Situ X-ray Diffraction

“…21 Altough good control over the crystal structure has been achieved for Au-catalyzed GaAs NWs, 22 controlling the droplet shape and crystal structure in self-catalyzed VLS grown NWs is more challenging, but could ultimately be performed at CMOS compatible temperatures. 23 However, not only the crystalline phase is affected by the droplet. For large wetting angles, radial growth can be strongly enhanced 15 resulting in a variation of the NW diameter along its length, so-called tapering.…”