Defects in Heteroepitaxy of III-Vs on Si by Templated Liquid-Phase Growth

The direct growth of III-V semiconductors on Si substrates provides an avenue for utilizing the tunable, direct bandgaps of III-Vs as well as existing economies of scale for Si. Direct, heteroepitaxial growth is more scalable than bonding. Our development of templated liquid-phase (TLP) heteroepitaxial growth of III-Vs on Si offers additional cost savings over metallorganic vapor-phase epitaxy (MOVPE) and, unlike vapor-liquid-solid (VLS) techniques, templated structures of III-V can be easily grown in orientations other than (111). <br/> <br/>The TLP process uses evaporation—on a photolithographically-patterned surface—to supply a layer of group-III metal, then the sample is heated above the metal melting point and exposed to a group-V vapor-phase precursor, forming a liquid solution. Once saturated, solid III-V grows out of the solution. In this way, TLP growth differs from VLS nanowire growth, in which both group-V and group-III elements are supplied by gas phase and continually crystallized in solid wires. In TLP growth, a thin layer of solution is maintained during growth using dielectric capping layers. Without the dielectric caps, wire-like vertical growths or dewetting of the liquid metal can occur. <br/> <br/>Our previous work has shown that TLP can result in relaxed, oriented growth of InP with large grain sizes in pre-defined, μm-scale structures [1]. Here, we investigate the presence of defects, which are prevalent due to the large (nearly 8%) lattice mismatch between InP and Si. We utilize a lateral overgrowth scheme in which the epi-layer takes the orientation of the substrate from a seed area where they are in contact, then growth propagates with minimal defects over a non-crystalline layer. <br/> <br/>In our TLP growth process, substrates are patterned with photolithography to define template shapes. Indium metal is typically deposited via e-beam evaporation, though it can also be electroplated, and then followed by a thin capping layer of SiO_x. We find that spin-coating with solgel SiO_x is ideal for conformally coating and confining patterned indium. To convert to InP, the Si/In/SiO_x stacks are heated to 750 °C in an atmosphere of PH₃ diluted in H₂. Short anneal times are useful to identify nucleation sites and density, while longer anneals are used to show growth evolution. <br/> <br/>We find that each template typically converts from a single nucleus of InP. X-ray diffraction shows that most InP is oriented to the (001) substrate, but some (111)-oriented InP is present. Electron channeling contrast imaging (ECCI) identifies crystalline defects and confirms that converted areas are typically single grains. Planar defects such as twins, which are very common in the epitaxy of III-Vs on Si, are observed spanning entire grains. Transmission electron microscopy (TEM) of the Si-InP interface shows that planar defects often propagate from roughened areas of the Si surface. <br/> <br/>The growth and nucleation mechanisms in TLP growth differ from those of vapor-phase epitaxy techniques, but its use of vapor-phase flux still offers precise control of the process. With this improved understanding of the defect formation processes, TLP growth now offers an avenue toward lower-cost and faster III-V growth, as material quality is improved to compete with established vapor-phase growth methods. <br/> <br/> <br/>References <br/>[1] Schneble et al. JVST A. <b>2021 </b>