Evaluation of Misfit Relaxation in α-Ga₂O₃ Epitaxial Growth on α-Al₂O₃ Substrate

Abstract

Corundum-structured -Ga 2 O 3 epitaxial thin films were grown on c-plane -Al 2 O 3 (sapphire) substrates by a mist chemical vapor deposition method. To reveal the defect structures, the -Ga 2 O 3 film was observed by high-resolution transmission electron microscopy (TEM). We found that the -Ga 2 O 3 thin film was in-plane compressive stressed from the -Al 2 O 3 substrate. Although misfit dislocations were periodically generated at the -Ga 2 O 3 /-Al 2 O 3 interface owing to the large lattice mismatches between -Ga 2 O 3 and -Al 2 O 3 , 3.54% (c-axis) and 4.81% (a-axis), most of the misfit dislocations did not thread through the layer. An extra-half plane was f 2110g consisting only of Ga. Screw dislocations were not confirmed, i.e., the density was under 10 7 cm À2 . The threading dislocation density was 7 Â 10 10 cm À2 .

Conductivity control of Sn-doped α-Ga2O3 thin films grown on sapphire substrates

“…FWHM values for the symmetric-plane diffractions were as small as 30 arcsec and those for the asymmetric-plane diffractions were as high as 1000 arcsec. According to the transmission electron microscopy (TEM) analysis we previously reported, 18) undoped α-Ga 2 O 3 films showed low screw dislocation densities of under 10 7 cm −2 and high edge dislocation densities with a typical value of 7 × 10 10 cm −2 . It is expected that edge dislocations do not markedly alter the crystal plane periodicity along the growth direction, that is, the direction perpendicular to the substrate surface, but they markedly break the periodicity along the direction parallel to the substrate surface.…”

“…On the contrary, with the decrease in the carrier concentration below 2 × 10 18 cm −3 , the mobility decreased. Although the edge dislocation density, which was as high as around 10 10 cm −2 in α-Ga 2 O 3 films directly on sapphire, 18) was somewhat reduced in the films on the annealed buffer layers, the edge dislocations may still cause severe carrier compensation by acting electron trapping centers. In other words, the mobility in this region is considered to be dominated by dislocation scattering.…”

On the origin of dislocation generation and annihilation in α -Ga2O3 epilayers on sapphire

“…1(d). Within each individual domain, the atomic steps are straight and elongated along the [11][12][13][14][15][16][17][18][19][20] and no surface depressions within the terraces are observed. Existing theories developed for dislocation mediated surface morphologies have been employed to interpret the formation of pinned steps, spiral growth hillocks, and surface depression.…”

Preparation of TaO2 thin films using NbO2 template layers by a pulsed laser deposition technique

“…One of the most effective ways to obtain a metastable compound is to stabilize the crystal structure of the compound in the form of a film by using a template substrate. For example, a metastable -Ga 2 O 3 with a corundum structure is obtained as a thin film grown on a corundum Al 2 O 3 substrate [9]. For rutile-type TaO 2 , it is expected that this metastable compound might be stabilized as a thin film grown on a rutile-type substrate.…”