Variation of Band Gap and Lattice Parameters of β−(Al_xGa_1−x)₂O₃ Powder Produced by Solution Combustion Synthesis

Abstract

Single-phase monoclinic aluminum-gallium oxide powders, b -(Al x Ga 1 -x ) 2 O 3 , have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. a -(Al x Ga 1 -x ) 2 O 3 is observed for x = 1, with mixed a + b for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively, and are compared with a first-principles density-functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.

Band Gap and Band Offset of Ga2O3 and (AlxGa<

“…This discontinuity in the slope is attributed to Al occupying the tetrahedral sites for x > 0.5. This trend was recently observed by Krueger et al [16] The calculated formation enthalpies of Ga 2 O 3 and Al 2 O 3 , defined as the total energy of the compound minus the total energies of the elemental bulk phases, are listed in Table I. We find that the formation enthalpy of α-Ga 2 O 3 is only 46 meV/f.u.…”

“…Therefore, for Al concentrations approaching 100%, we predict that (Al x Ga 1−x ) 2 O 3 alloys strongly favor the corundum or α phase. This explains why single monoclinic phase at 0 ≤ x < 0.8 and mixed corundum and monoclinic phases for 0.8 ≤ x < 1 have been observed by solution combustion synthesis [16]. We note, however, that thin films of β-(Al x Ga 1−x ) 2 O 3 alloys with Al content up to 96% have been reported using pulsed laser deposition (PLD) [17].…”

“…1. Bulk and thin films of β-(Al x Ga 1−x ) 2 O 3 have been obtained using solution combustion synthesis [16], pulsed laser deposition (PLD) [17], and oxygen plasmaassisted molecular beam epitaxy (MBE) [10][11][12], while α- up to 81% [18,19]. Band gaps of (Al x Ga 1−x ) 2 O 3 for selected Al content have been reported [16][17][18][19][20], but band offsets between Ga 2 O 3 and (Al x Ga 1−x ) 2 O 3 , which are much more challenging to obtain experimentally, are still unknown.…”

Identification and modulation of electronic band structures of single-phase β-(AlxGa1−x)2O3 alloys grown by laser molecular beam epitaxy

“…In the case of (Al x Ga 1Àx ) 2 O 3 , small values of the bowing parameter are observed in a-, b-, and c-(Al x Ga 1Àx ) 2 O 3 . 10,19,21,28 Typically, a small value of the bowing parameter and thus a small deviation from the linearity of the bandgap of alloys can indicate a desirable miscibility, 37 which is in agreement with the XRD results. The bandgap of 4.5-5.5 eV is corresponding to the absorption wavelength between 225 nm and 275 nm in the solar blind spectral range.…”

“…On the aspect of electronic band structure of b-(Al x Ga 1Àx ) 2 O 3 , both GGA and HSE calculations were performed in terms of first principles, which has been widely employed to predict a variety of electronic, optical, and magnetic properties of polycrystalline oxide semiconductors. [24][25][26][27][28] The specific electronic band structures of the alloy films with composition of x ¼ 0 and x ¼ 0.5 are shown in Figs. 3(a) and 3(b), respectively.…”