Azimuthal Anisotropy of Rhombohedral (Corundum Phase) Heterostructures

Abstract

The corundum structure is rhombohedral/trigonal and thus has lower symmetry than the well‐investigated hexagonal crystals such as wurtzite GaN‐ and ZnO‐based materials. By investigating the growth of α‐phase ( Al x Ga 1 − x ) 2 normalO 3 alloy thin films on various orientations of Al2O3 substrates, the anisotropy around the [00.1]‐axis is investigated. In particular, the pseudomorphic growth on the r plane (01.2) and r ′ (10.2) plane substrates is compared. The findings agree with elasticity theory. Also, different growth kinetics are found on these two planes in terms of growth rate and preferential cation incorporation.

Suppression of Rotational Domains of CuI Employing Sodium Halide Buffer Layers

“…Even though previous publications considered a C 6 symmetry for c-sapphire, which yields a minimum number of two rotational domains for a cubic epilayer, the unit cell of c-sapphire actually possesses a C 3 symmetry. The effect of the trigonal versus hexagonal symmetry of sapphire on heteroepitaxy has been recently pointed out. , Consequently, single-crystalline NaCl on c-sapphire does not violate the corresponding symmetry. The epitaxy of the CuI/NaCl/c-sapphire heterostructure with CuI grown on top of these single-crystalline in situ NaCl template layers also differs from the rotational domain epitaxy reported in the literature as shown in Figure (b) and exhibits three intense reflections with a 120° spacing as well as three weaker reflections, also with a 120° spacing but rotated 60° relative to the intense reflections.…”

Strain states and relaxation for $$\alpha$$-(Al$$_x$$Ga$$_{1-x}$$)$$_2$$O$$_3$$ thin films on prismatic planes of $$\alpha$$-Al$$_2$$O$$_3$$ in the full composition range: Fundamental difference of a- and m-epitaxial planes in the manifestation of shear strain and lattice tilt

“…As one can clearly observe, the m-plane is actually the best suited plane to test the accuracy of the C 14 component since the relative difference in e ′ 5 compared to a vanishing C 14 component is the largest. The r-and r ′ -planes we investigated in previous studies in detail [31,39,40], however, show only little sensitivity of e ′ 5 to C 14 , which is almost vanishing for the r-plane inclination angle in Fig. 6.…”

“…Further, as special property of the rhombohedral R3c crystal symmetry, not all r-planes and s-planes are actual glide planes, since there is a difference between r-and r ′ -planes [40] as well as s-and s ′ -planes in the crystal. Only the three (01.2) , (11.2) and (10.2) r-as well as the (01.1) , (11.1) , and (10.1) s-planes are actual crystallographic glide planes within the unit cell in contrast to a hexagonal crystal system [62].…”

“…In most reports, α-Ga 2 O 3 and α-(Al x Ga 1−x ) 2 O 3 is grown on the basal c-plane of α-Al 2 O 3 [9, 17-22, 24, 28, 29, 34, 35]. Lately, also the pyramidal r-plane [14,31,[36][37][38][39][40] as well as the prismatic a- [14,27,32,41,42] and m-plane [26, www.mrs.org/jmr © The Author(s) 2021 2 Invited Paper 33,[42][43][44] of sapphire were utilized as epitaxial plane for the material. Especially the last one became interesting for potential device applications due to doped m-plane α-Ga 2 O 3 exhibiting up to three times higher mobility than similar layers on c-plane sapphire [26].…”

“…Up to now, for α-Ga 2 O 3 , they are exclusively available from theoretical calculations [47] as given later in this report. Due to the threefold pseudohexagonal rhombohedral R3c symmetry of the corundum structure, a distinct difference in biaxially strained α-(Al x Ga 1−x ) 2 O 3 /α-Al 2 O 3 heterostructures for epitaxial a-and m-planes is expected [40,45,46]. This is caused by the nonvanishing C 14 component of C ij in contrast to "true" sixfold hexagonal systems such as wurtzite GaN or ZnO [48].…”