Tackling Disorder in γ‐Ga₂O₃

Abstract

Ga2O3 and its polymorphs are attracting increasing attention. The rich structural space of polymorphic oxide systems such as Ga2O3 offers potential for electronic structure engineering, which is of particular interest for a range of applications, such as power electronics. γ‐Ga2O3 presents a particular challenge across synthesis, characterization, and theory due to its inherent disorder and resulting complex structure–electronic‐structure relationship. Here, density functional theory is used in combination with a machine‐learning approach to screen nearly one million potential structures, thereby developing a robust atomistic model of the γ‐phase. Theoretical results are compared with surface and bulk sensitive soft and hard X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, spectroscopic ellipsometry, and photoluminescence excitation spectroscopy experiments representative of the occupied and unoccupied states of γ‐Ga2O3. The first onset of strong absorption at room temperature is found at 5.1 eV from spectroscopic ellipsometry, which agrees well with the excitation maximum at 5.17 eV obtained by photoluminescence excitation spectroscopy, where the latter shifts to 5.33 eV at 5 K. This work presents a leap forward in the treatment of complex, disordered oxides and is a crucial step toward exploring how their electronic structure can be understood in terms of local coordination and overall structure.

Stabilizing cubic γ-Ga2O3:Cr3+ spinel nanocrystals by size confinement into mesoporous silica nanoreactor channels

“…The trigonal a-Ga 2 O 3 (space group R% 3c) is characterized by a corundum structure with only octahedral GaO 6 sites, while b-phase by a monoclinic structure (space group C2/ m) with mixed coordination of octahedral GaO 6 and tetrahedral GaO 4 sites with a ratio 1 : 1 and the cubic g-phase (space group Fd% 3mZ) by a defective spinel structure with both octahedral and tetrahedral sites characterized by a high degree of disorder. [36][37][38][39][40] The unit cell volume increases by moving from the compact b-Ga 2 O 3 (B209 Å 3 ) to a-Ga 2 O 3 (B289 Å 3 ) and finally to the defective g-Ga 2 O 3 (B559 Å 3 ).…”

“…34,35 The crystalline structure of the g-Ga 2 O 3 polymorph has been widely investigated and debated due to the complicated defect Fd% 3m spinel structure. [36][37][38][39][40] g-Ga 2 O 3 stabilization was also proved in glassy hosts 41 showing photocatalytic and catalytic activity. [42][43][44] The defects present in the g-Ga 2 O 3 spinel structure were exploited to develop size-tuneable luminescent nanocrystals 45 and white-light-emitting nanophosphors when coupled through energy transfer with orange-red emitting organic dyes.…”

Determination of anisotropic optical properties of MOCVD grown m-plane α-(Al x Ga1−x )2O3 alloys

“…Most intensely investigated is certainly the thermodynamically stable monoclinic β-phase (C2/m). Furthermore, with the γ-phase(Fd m 3 ¯) (just recently explored in greater detail by Ratcliff et al 13) ) and the δ-phase (Ia3 ¯) there are two cubic polymorphs, along with the two orthorhombic polymorphs ò-(P6 3 mc) and κ-phase (Pna2 1 ). 14) The last of the six polymorphs of Ga 2 O 3 is the rhombohedral corundum-structured α-phase (R c 3 ¯).…”

Design of Cr–Ba-doped γ-Ga2O3 persistent luminescence nanoparticles for ratiometric temperature sensing and encryption information transfer

“…[21][22][23] Moreover, the voids and defective structures of g-Ga 2 O 3 facilitate the introduction of dopant ions owing to their optical applications. 24,25 Ni-doped g-Ga 2 O 3 was reported with improved optical properties for photocatalysis. 26 The bandgap of Zn ion-doped g-Ga 2 O 3 was tunable and reported for light-emitting diode (LED).…”