Atomically stepped, pseudomorphic, corundum-phase (Al1-xGax)2O3 thin films (0 ≤ x < 0.08) grown on R-plane sapphire

Abstract

Atomically smooth, pseudomorphic (Al1−xGax)2O3 thin films were grown for 0 ≤ x < 0.08 on R-plane sapphire (01.2) by pulsed laser deposition at growth temperatures up to 1000 °C. Films up to 720 nm thickness show atomically stepped surfaces with monolayer terraces, similar to the substrates prior to growth, in wide ranges of growth pressure and temperature. A careful analysis of 13 symmetric, skew-symmetric, and asymmetric X-ray peaks agrees quite well with the continuum elastic strain theory of pseudomorphic distortion in corundum heterostructures by M. Grundmann [J. Appl. Phys. 124, 185302 (2018)]. The Ga-contents x and weak deviations from the expected ratios of rhombohedral c/a lattice constants are obtained from the best fits of the spacing of the (02.4), (04.8), and (00.6), (00.12) film and substrate reflections, in reasonable agreement with chemical energy dispersive X-ray spectrometry analyses. In addition, the measured tilts of the asymmetric film lattice planes corroborate the elastic theory.

A Most General and Facile Recipe for the Calculation of Heteroepitaxial Strain

“…In recent years, low‐symmetry semiconductors and their heterostructures have found interest in technology, namely sesquioxides in the system [ 1 ] with monoclinic ( β ‐phase) and with rhombohedral ( α ‐phase) crystal structures (and others) for manifold device applications. The stress–strain analysis for monoclinic [ 2,3 ] and rhombohedral [ 3–6 ] heterostructures has been reported. In particular, the trigonal/rhombohedral structure exhibits no more basal plane isotropy, as is the case for the hexagonal structure, known from heterostructures based on nitrides, e.g., (Al,Ga,In)N/GaN, [ 7 ] and oxides, e.g., (Mg,Zn,Cd)O/ZnO.…”

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

“…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].…”

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

“…Successful fabrication of rhombohedral Ga 2 O 3 was reported by mist chemical vapor deposition (CVD), [ 13,17,19,21–23 ] halide vapor phase epitaxy (HVPE), [ 14,16,24 ] metalorganic vapor phase epitaxy (MOVPE), [ 15 ] mist epitaxy, [ 19 ] and the sol–gel method, [ 12 ] whereas ternary α‐ has been realized by mist CVD, [ 25–28 ] PLD, [ 29,30 ] and molecular beam epitaxy (MBE) [ 31 ] until now. As substrates, a ‐, c ‐, m ‐, or r ‐plane sapphire are possible to use.…”