Growth dynamics of SiGe nanowires by the vapour–liquid–solid method and its impact on SiGe/Si axial heterojunction abruptness

Abstract

The vapour-liquid-solid (VLS) method is by far the most extended procedure for bottom-up nanowire growth. This method also allows for the manufacture of nanowire axial heterojunctions in a straightforward way. To do this, during the growth process, precursor gases are switched on/off to obtain the desired change in the nanowire composition. Using this technique, axially heterostructured nanowires can be grown, which are crucial for the fabrication of electronic and optoelectronic devices. SiGe/Si nanowires are compatible with complementary metal oxide semiconductor (CMOS) technology, which improves their versatility and the possibility of integration with current electronic technologies. Abrupt heterointerfaces are fundamental for the development and correct operation of electronic and optoelectronic devices. Unfortunately, the VLS growth of SiGe/Si heterojunctions does not provide abrupt transitions because of the high solubility of group IV semiconductors in Au, with the corresponding reservoir effect that precludes the growth of sharp interfaces. In this work, we studied the growth dynamics of SiGe/Si heterojunctions based on already developed models for VLS growth. A composition map of the Si-Ge-Au liquid alloy is proposed to better understand the impact of the growing conditions on the nanowire growth process and the heterojunction formation. The solution of our model provides heterojunction profiles that are in good agreement with the experimental measurements. Finally, an in-depth study of the composition map provides a practical approach to the drastic reduction of heterojunction abruptness by reducing the Si and Ge concentrations in the catalyst droplet. This converges with previous approaches, which use catalysts aiming to reduce the solubility of the atomic species. This analysis opens new paths to the reduction of heterojunction abruptness using Au catalysts, but the model can be naturally extended to other catalysts and semiconductors.

Electromagnetic enhancement effect on the atomically abrupt heterojunction of Si/InAs heterostructured nanowires

“…The full miscibility of Ge and Si, and its high solubility in the catalyst metal, are responsible for the graded HJs extending several tens of nanometres depending on the NW diameter. 22 The SiGe/Si heterojunction is not abrupt, but a continuous transition between the compositions of the NW segments constitutes the heterojunction. Therefore, one can associate a certain volume of material to the HJ region itself, which is chemically recognizable, and the Raman signal arising from this volume forming the HJ permitted to study the true local field enhancement (intensity per unit scattering volume).…”

Vertical van der Waals Heterostructure of Single Layer InSe and SiGe

“…The experimentally realized SiGe alloy was reported as an appropriate material for solar cell applications . Recent studies have shown that Ge atoms can be incorporated into Si-based nanostructures with negligibly small induced strains. , The exchange of Si and Ge atoms in Si-based or Ge-based nanostructures may allow the possible experimental realization of the 2D form of SiGe. In addition, the single layer form of SiGe was theoretically predicted to exhibit a dynamically stable buckled structure as a free-standing layer which can be formed upon the incorporation of Si atoms into the germanene layer .…”

About the Interaction Between a Laser Beam and Group IV Nanowires: A Study of the Electromagnetic Field Enhancement in Homogeneous and Heterostructured Nanowires

“…It arises from the HJ itself, which is a compositionally graded NW rod. It is important to recall that the HJ width is close or below to the NW diameter (≈50 nm in this case), while the excited length of the two homogeneous segments of the NW lies around 500 nm (approximately half of the laser spot diameter) for a laser beam centered on the HJ. As a result, the probed volume of each of the homogeneous segments is at least 10 times larger than that of the HJ; however, the intensity of the Raman signal associated with the HJ is of the same order of magnitude, or even higher, as the signals arising from the homogeneous segments, see Figure .…”

“…The transition between the two NW segments is not sharp, but it appears as a region with graded composition in between those of the two segments . Usually, it is assumed to have a thickness of the order of the NW diameter; although, it is more appropriate to say that the HJ width is a fraction of the NW diameter; which depends on the growth conditions . Therefore, when the laser beam impacts on the HJ is probing the Si segment, the SiGe segment, and the HJ itself.…”