Maxim Korytov | Searcharxiv

arXiv2026

Stoichiometric Epitaxial Strontium Titanate Thin Films on Silicon by High-Temperature Sr Segregation

Thin-film strontium titanate (SrTiO$_3$, STO) layers grown on silicon require accurate stoichiometry and single-crystalline order to exploit their functional properties optimally. Oxide molecular beam epitaxy can provide an epitaxial interface, but suffers from source oxidation and resulting flux instabilities, yielding only a narrow growth process window for cationic stoichiometry control. Here, we investigate post-growth annealing in oxygen as a pathway to drive the STO layer toward stoichiometry in intentionally Sr-rich epitaxial STO films on silicon (001). Annealing over a broad temperature range revealed two distinct Sr-segregation mechanisms. Below 800 {\deg}C, excess Sr segregates toward the surface, forming SrO outgrowths that progressively sublimate at elevated temperatures. Above 800 {\deg}C, a second mechanism dominates: Sr accumulates within the interfacial SiO$_2$ layer formed by oxygen diffusion at the STO/Si interface. Together, these mechanisms effectively remove excess Sr from the STO lattice, yielding a more stoichiometric perovskite layer. Our results demonstrate that growing slightly Sr-rich STO templates followed by controlled annealing provides a practical route to improve crystalline quality, offering a scalable strategy for high-quality STO integration on silicon.

cond-mat.mtrl-sci↗

arXiv2015

Comparison of the luminous efficiency of Ga- and N-polar In$_{x}$Ga$_{1-x}$N/In$_{y}$Ga$_{1-y}$N quantum wells grown by plasma-assisted molecular beam epitaxy

We investigate the luminescence of Ga- and N-polar In$_{x}$Ga$_{1-x}$N/In$_{y}$Ga$_{1-y}$N quantum wells (QWs) grown by plasma-assisted molecular beam epitaxy on freestanding GaN as well as 6H-SiC substrates. In striking contrast to their Ga-polar counterparts, the N-polar QWs prepared on freestanding GaN do not exhibit any detectable photoluminescence. Theoretical simulations of the band profiles combined with resonant excitation of the QWs allow us to rule out carrier escape and subsequent surface recombination as the reason for the absence of luminescence. To explore the hypothesis of a high concentration of nonradiative defects at the interfaces between wells and barriers, we analyze Ga- and N-polar QWs prepared on 6H-SiC as a function of the well width. Intense luminescence is observed for both Ga- and N polar samples. As expected, the luminescence of the Ga-polar QWs quenches and red-shifts with increasing well width due to the quantum confined Stark effect. In contrast, both the intensity and the energy of the luminescence from the N-polar samples are essentially independent of well width. Transmission electron microscopy reveals that the N-polar QWs exhibit abrupt interfaces and homogeneous composition, excluding emission from In-rich clusters as the reason for this anomalous behavior. The microscopic origin of the luminescence in the N-polar QWs is elucidated using spatially resolved cathodoluminescence spectroscopy. Regardless of well width, the luminescence is found to not originate from the N-polar QWs, but from the semipolar facets of v-pit defects. These results cast serious doubts on the potential of N-polar QWs grown by plasma-assisted molecular beam epitaxy for the development of long-wavelength light emitting diodes. What remains to be seen is whether unconventional growth conditions may enable a significant reduction in the concentration of nonradiative defects.

cond-mat.mtrl-sci↗