Preferred orientations of laterally grown silicon films over amorphous substrates using the vapor–liquid–solid technique

Abstract

A novel method has been optimized so that adhesion layers are no longer needed to reliably deposit patterned gold structures on amorphous substrates. Using this technique allows for the fabrication of amorphous oxide templates known as micro-crucibles, which confine a vapor–liquid–solid (VLS) catalyst of nominally pure gold to a specific geometry. Within these confined templates of amorphous materials, faceted silicon crystals have been grown laterally. The novel deposition technique, which enables the nominally pure gold catalyst, involves the undercutting of an initial chromium adhesion layer. Using electron backscatter diffraction it was found that silicon nucleated in these micro-crucibles were 30% single crystals, 45% potentially twinned crystals and 25% polycrystals for the experimental conditions used. Single, potentially twinned, and polycrystals all had an aversion to growth with the {1 0 0} surface parallel to the amorphous substrate. Closer analysis of grain boundaries of potentially twinned and polycrystalline samples revealed that the overwhelming majority of them were of the 60° Σ3 coherent twin boundary type. The large amount of coherent twin boundaries present in the grown, two-dimensional silicon crystals suggest that lateral VLS growth occurs very close to thermodynamic equilibrium. It is suggested that free energy fluctuations during growth or cooling, and impurities were the causes for this twinning.

Effects of Au catalyst geometry on Ge films grown laterally on Si using the vapor–liquid–solid mechanism

“…As can be seen from figure 5(a), numerous small Ge films were grown in the narrow, two-opening micro-crucibles, suggesting that GeH 4 molecules were rapidly absorbed by Au in these micro-crucibles; then the liquid reached supersaturation quickly and caused many nucleation points. This growth morphology is similar to that observed by LeBoeuf et al when a high growth rate was used to grow Si films laterally on SiO 2 [16]. As mentioned above, the ideal way to grow Ge films laterally on Si is to nucleate only one crystal seed so that the films can be grown in a more controlled way.…”

“…In order to address this challenge, a lateral growth technique has recently been developed to grow thin films on a substrate [14][15][16][17][18]. Lateral thin film growth is similar to traditional nanowire growth because the VLS mechanism is also used in the growth process.…”

New Relaxation Mechanism Enabling High-Quality, Laterally Grown Ge on Si

“…This innovative growth technique, first demonstrated here, is made possible by selective, metal-catalyzed chemical vapor deposition (CVD). − A confined and guided structure (Figure a), termed a microcrucible − (see Figure S1 for the fabrication process), was recently reported to grow Si nanowires or micron-scale Si films laterally on SiO 2 . In this paper, the microcrucible was adapted to laterally grow high-quality Ge films on a Si substrate both to be able to increase the functionality of the Si platform, for example, fabrication of Ge photodetectors on Si for optical communication, as well as demonstrate a proof of concept for other lattice-mismatched materials like InP, InAs, etc.…”