Doubling the mobility of InAs/InGaAs selective area grown nanowires

Abstract

Selective area growth (SAG) of nanowires and networks promise a route toward scalable electronics, photonics, and quantum devices based on III-V semiconductor materials. The potential of high-mobility SAG nanowires however is not yet fully realised, since interfacial roughness, misfit dislocations at the nanowire/substrate interface and nonuniform composition due to material intermixing all scatter electrons. Here, we explore SAG of highly lattice-mismatched InAs nanowires on insulating GaAs(001) substrates and address these key challenges. Atomically smooth nanowire/substrate interfaces are achieved with the use of atomic hydrogen (a-H) as an alternative to conventional thermal annealing for the native oxide removal. The problem of high lattice mismatch is addressed through an In x Ga 1−x As buffer layer introduced between the InAs transport channel and the GaAs substrate. The Ga-In material intermixing observed in both the buffer layer and the channel is inhibited via careful tuning of the growth temperature. Performing scanning transmission electron microscopy and x-ray diffraction analysis along with low-temperature transport measurements we show that optimized In-rich buffer layers promote high-quality InAs transport channels with the field-effect electron mobility over 10 000 cm 2 V −1 s −1 . This is twice as high as for nonoptimized samples and among the highest reported for InAs selective area grown nanostructures.

Atomic-Scale Characterization of Planar Selective-Area-Grown InAs/InGaAs Nanowires

“…On the other hand, both the APT and EDS techniques reveal some gallium in the InAs layer, which is anomalous given that a Ga flux was not introduced during this step. This can also be ascribed to two possible causes: (1) The strain effect among the heterogeneous layers will mediate chemical distribution. ,, (2) The In atoms from the InAs diffuse inward by exchanging the position with Ga atoms from InGaAs, also reported in other types of NW growth …”

“…(1) The strain effect among the heterogeneous layers will mediate chemical distribution. 34,38,39 (2) The In atoms from the InAs diffuse inward by exchanging the position with Ga atoms from InGaAs, also reported in other types of NW growth. 25 Finally, the APT analysis reveals almost 3% more indium compared to the EDS data.…”

“…The NW epitaxial growth followed a three-step protocol: (i) A GaAs­(Sb) layer with a nominal thickness of 40 nm was initiated as the first buffer layer and used to mediate the surface flatness of the substrate . (ii) A second ternary In x Ga 1– x As layer with a nominal thickness of 100 nm was grown to minimize crystal defects/dislocations by improving the lattice mismatch between GaAs and InAs layers . (iii) Finally, the structure was terminated with a 20 nm nominal thick pristine InAs layer.…”

“…26 (ii) A second ternary In x Ga 1−x As layer with a nominal thickness of 100 nm was grown to minimize crystal defects/dislocations by improving the lattice mismatch between GaAs and InAs layers. 34 (iii) Finally, the structure was terminated with a 20 nm nominal thick pristine InAs layer. In this work, we investigate two samples, A and B, which were grown at a different As pressure for the InAs layer but otherwise identical growth parameters (see Table 1).…”

“…However, quantifying this subtle In variation across a very small volume is a challenging task that requires both good chemical sensitivity and excellent spatial resolution. In this work, InAs/InGaAs planar nanowire arrays were grown on a GaAs(001) substrate following a threestep protocol, 34 with their size and position predefined by an oxide mask. APT and aberration-corrected TEM were used to characterize two types of nanowire samples to reveal their compositional and crystallographic information at the atomic scale.…”