X-ray photoelectron diffraction study of thinAl2O3films grown on Si(111) by molecular beam epitaxy

Abstract

The in-plane and out-of-plane crystallographic orientations of Al 2 O 3 films grown by molecular beam epitaxy on Si͑111͒ have been determined by combining x-ray photoelectron diffraction ͑XPD͒ with transmission electron microscopy ͑TEM͒. On the one hand, polar and azimuth XPD curves for Al 2p, O 1s, and Si 2p core levels ͑recorded on a 6-nm-thick film͒ clearly indicate that Al 2 O 3 grows ͑111͒ oriented on Si͑111͒ but with two in-plane orientations: a "direct" one, i.e., ͓112͔Al 2 O 3 / /͓112͔Si͑111͒ and a "mirror" one, i.e., ͓112͔Al 2 O 3 ͑111͒ / /͓112͔Si͑111͒. On the other hand, a close inspection of the 404 Al 2 O 3 TEM diffraction spots ͑recorded on a 2-nm-thick film͒ reveals that these two in-plane orientations are slightly rotated with respect to the Si͑111͒ orientations. These two results are consistent with an oxygen plane as the interfacial plane between Al 2 O 3 ͑111͒ and Si͑111͒.

Functional spinel oxide heterostructures on silicon

“…26,29,30,32,33 A detailed view of the CFO layer reveals the presence of crystal as well as the sequence of the spinel planes in the <111> direction, might both have an impact on the formation of these two mirror-like domains observed here. 28 After demagnetization field corrections, § the magnetization hysteresis loops measured with a field perpendicular to the substrate are similar to those along the [11−2] in-plane direction (Fig. 4), thus implying that there is no significant anisotropy between those two directions in the film, which is consistent with the tiny strain state of the CFO film here, in agreement with previous studies.…”

“…The (111)-oriented spinels on Si(111) grow with two possible in-plane domains rotated by 180°, as it was observed in thicker AO films. 28 It thus implies that CFO films replicate here the in-plane arrangement of the AO buffer layer. Fig.…”

“…Gamma-Al 2 O 3 (γ-Al 2 O 3 ) is a thermally and chemically stable oxide with a cubic spinel structure (a = 0.7939 nm) and good insulating electric properties, which can be epitaxially grown by molecular beam epitaxy (MBE) on Si with a flat surface, an abrupt interface, and two in-plane domains, where two unit cells (uc) of spinel roughly match with three uc of Si (2.6% of mismatch). [25][26][27][28][29] γ-Al 2 O 3 appears as an ideal buffer layer for the integration of spinel oxides on silicon. Indeed, we demonstrate here with ferrimagnetic spinel CFO layers (a = 0.8392 nm) that i) functional spinel oxides can be epitaxially grown on isostructural γ-Al 2 O 3 (AO), ii) this fully spinel heteroepitaxial structure can be monolithically integrated on Si(111), even with ultrathin (1.4 nm) AO buffer layers, and iii) flat epitaxial CFO(111) films grown on these AO-buffered silicon substrates present magnetization values close to that of the bulk material.…”

High oxidation state at the epitaxial interface of γ-Al2O3 thin films grown on Si(111) and Si(001)

“…4,5 If combined with some high-oxides, this could provide an interesting way to reach small equivalent oxide thickness in complementary metal-oxide semiconductor devices. 4 On both Si͑111͒ and Si͑001͒ substrates, ␥-Al 2 O 3 is ͑111͒ oriented 4 with two in-plane orientations 8 and four in-plane orientations, 5 respectively. 7 Al 2 O 3 grows on silicon with a spinel-like structure ͑␥-Al 2 O 3 ͒, and a lattice parameter a Al 2 O 3 of 0.791 nm.…”