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Two distinct ultra-thin Ge1−xSnx (x ≤ 0.1) epilayers were deposited on (001) Si substrates at 457 and 313 °C through remote plasma-enhanced chemical vapor deposition. These films are considered potential initiation layers for synthesizing thick epitaxial GeSn films. The GeSn film deposited at 313 °C has a thickness of 10 nm and exhibits a highly epitaxial continuous structure with its lattice being compressed along the interface plane to coherently match Si without mismatch dislocations. The GeSn film deposited at 457 °C exhibits a discrete epitaxial island-like morphology with a peak height of ∼30 nm and full-width half maximum (FWHM) varying from 20 to 100 nm. GeSn islands with an FWHM smaller than 20 nm are defect free, whereas those exceeding 25 nm encompass nanotwins and/or stacking faults. The GeSn islands form two-dimensional modulated superlattice structures at the interface with Si. The GeSn film deposited at 457 °C possesses a lower Sn content compared to the one deposited at lower temperature. The potential impact of using these two distinct ultra-thin layers as initiation layers for the direct growth of thicker GeSn epitaxial films on (001) Si substrates is discussed. 

Perovskite materials, of which strontium titanate (STO) and its thin films are an example, have attracted significant scientific interest because of their desirable properties and the potential to tune thermal conductivity by employing several techniques. Notably, strontium titanate thin films on silicon (Si) substrates serve as a fundamental platform for integrating various oxides onto Si substrates, making it crucial to understand the thermal properties of STO on Si. This work investigates the thermal conductivity of STO thin films on an Si substrate for varying film thicknesses (12, 50, 80, and 200 nm) at room temperature (∼300 K). The thin films are deposited using molecular beam epitaxy on the Si substrate and their thermal conductivity is characterized using the frequency domain thermoreflectance (FDTR) method. The measured values range from 7.4 ± 0.74 for the 200 nm thick film to 0.8 ± 0.1 W m−1 K−1 for the 12 nm thick film, showing a large effect of the film thickness on the thermal conductivity values. The trend of the values is diminishing with the corresponding decrease in the thin film thickness, with a reduction of 38%–93% in the thermal conductivity values, for film thicknesses ranging from 200 to 12 nm. This reduction in the values is relative to the bulk single crystal values of STO, which may range from 11 to 13.5 W m−1 K−1 [Yu et al., Appl. Phys. Lett. 92, 191911 (2008) and Fumega et al., Phys. Rev. Mater. 4, 033606 (2020)], as measured by our FDTR-based experiment. The study also explores the evaluation of volumetric heat capacity (Cp). The measured volumetric heat capacity for the 200 nm thin film is 3.07 MJ m−3 K−1, which is in reasonable agreement with the values available in the literature. 

Abstract Functional oxides are an untapped resource for futuristic devices and functionalities. These functionalities can range from high temperature superconductivity to multiferroicity and novel catalytic schemes. The most prominent route for transforming these ideas from a single device in the lab to practical technologies is by integration with semiconductors. Moreover, coupling oxides with semiconductors can herald new and unexpected functionalities that exist in neither of the individual materials. Therefore, oxide epitaxy on semiconductors provides a materials platform for novel device technologies. As oxides and semiconductors exhibit properties that are complementary to one another, epitaxial heterostructures comprised of the two are uniquely poised to deliver rich functionalities. This review discusses recent advancements in the growth of epitaxial oxides on semiconductors, and the electronic and physical structure of their interfaces. Leaning on these fundamentals and practicalities, the material behavior and functionality of semiconductor–oxide heterostructures is discussed, and their potential as device building blocks is highlighted. The culmination of this discussion is a review of recent advances in the development of prototype devices based on semiconductor–oxide heterostructures, in areas ranging from silicon photonics to photocatalysis. This overview is intended to stimulate ideas for new concepts of functional devices and lay the groundwork for their realization.