Abstract
Ge1–xSnx nanowires incorporating a large amount of Sn would be useful for mobility enhancement in nanoelectronic devices, a definitive transition to a direct bandgap for application in optoelectronic devices and to increase the efficiency of the GeSn-based photonic devices. Here we report the catalytic bottom-up fabrication of Ge1–xSnx nanowires with very high Sn incorporation (x > 0.3). These nanowires are grown in supercritical toluene under high pressure (21 MPa). The introduction of high pressure in the vapor–liquid–solid (VLS) like growth regime resulted in a substantial increase of Sn incorporation in the nanowires, with a Sn content ranging between 10 and 35 atom %. The incorporation of Sn in the nanowires was found to be inversely related to nanowire diameter; a high Sn content of 35 atom % was achieved in very thin Ge1–xSnx nanowires with diameters close to 20 nm. Sn was found to be homogeneously distributed throughout the body of the nanowires, without apparent clustering or segregation. The large inclusion of Sn in the nanowires could be attributed to the nanowire growth kinetics and small nanowire diameters, resulting in increased solubility of Sn in Ge at the metastable liquid–solid interface under high pressure. Electrical investigation of the Ge1–xSnx (x = 0.10) nanowires synthesized by the supercritical fluid approach revealed their potential in nanoelectronics and sensor-based applications.
Highlights
A direct bandgap can be achieved in Ge1−xSnx alloy for Sn content as low as x = 0.06, a certain degree of Γ−L mixing is observed for Sn contents in the region 0.06 < x < 0.1.6,7 The drive to incorporate high Sn concentrations (x > 0.1) in Ge1−xSnx alloy nanowires can be partly attributed to the presence of this bandmixing at lower Sn content Ge1−xSnx alloys.[7−11] Recent theoretical calculations have supported that the indirectgap to direct-gap transition proceeds via the continuous transition−with increasing x
A kinetic dependent solute trapping mechanism is believed to be liable for Sn incorporation in Ge1−xSnx nanowires, where nanowires with faster growth rates lead to higher Sn incorporation in the nanowires.[8,37]
We have reported the fabrication of Ge1−xSnx nanowires grown by a SCF approach
Summary
IV metals such as Sn, can lead to a direct bandgap semiconductor.[1−5] Theoretically, increasing the amount of. Recent reports from our group have demonstrated highly crystalline Ge1−xSnx nanowires with a Sn content of ≈9 atom % via metal catalyzed vapor−liquid−solid (VLS) growth methods. “Solute trapping” of impurities during the VLS growth of nanowires is likely to be influenced by pressure. This could be due to a change in the metastable solubility of Sn at the liquid−solid growth interface. We report the ability to increase the concentration of Sn in Ge nanowires beyond 25 atom % by introducing high pressure as a growth constraint. High pressures (∼21 MPa) result in Ge1−xSnx nanowire growth with 0.1 ≤ x ≤ 0.35, much higher than previously reported for Sn incorporation in Ge 1D lattices. Given the scarcity of reports detailing the electronic characterization of bottom-up grown Ge1−xSnx nanowires in (FET)-like devices,[21] we report the most important FET electronic figures-of-merit for nominally undoped Ge1−xSnx nanowires with 10 atom % Sn incorporation
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