Structure and gap of low-x (Ga 1 x In x ) 2 O 3 alloys (original) (raw)
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Ab-Initio Calculations of Oxygen Vacancy in Ga2O3 Crystals
Latvian Journal of Physics and Technical Sciences, 2021
Gallium oxide β-Ga 2 O 3 is an important wide-band gap semiconductor. In this study, we have calculated the formation energy and transition levels of oxygen vacancies in β-Ga 2 O 3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach. The obtained electronic charge redistribution in perfect Ga 2 O 3 shows notable covalency of the Ga-O bonds. The formation of the neutral oxygen vacancy in β-Ga 2 O 3 leads to the presence of deep donor defects with quite low concentration. This is a clear reason why oxygen vacancies can be hardly responsible for n-type conductivity in β-Ga 2 O 3 .
Experimental electronic structure of In 2 O 3 and Ga 2 O 3
New Journal of Physics, 2011
Transparent conducting oxides (TCOs) pose a number of serious challenges. In addition to the pursuit of high-quality single crystals and thin films, their application has to be preceded by a thorough understanding of their peculiar electronic structure. It is of fundamental interest to understand why these materials, transparent up to the UV spectral regime, behave also as conductors. Here we investigate In 2 O 3 and Ga 2 O 3 , two binary oxides, which show the smallest and largest optical gaps among conventional n-type TCOs. The investigations on the electronic structure were performed on high-quality n-type single crystals showing carrier densities of ∼10 19 cm −3 (In 2 O 3 ) and ∼10 17 cm −3 (Ga 2 O 3 ). The subjects addressed for both materials are: the determination of the band structure along high-symmetry directions and fundamental gaps by angular resolved photoemission (ARPES). We also address the orbital character of the valence-and conduction-band regions by exploiting photoemission cross 5 2 sections in x-ray photoemission (XPS) and by x-ray absorption (XAS). The observations are discussed with reference to calculations of the electronic structure and the experimental results on thin films.
The electronic structure of "-Ga 2 O 3
The electronic structure of "-Ga 2 O 3 thin films has been investigated by ab initio calculations and photoemission spectroscopy with UV, soft, and hard X-rays to probe the surface and bulk properties. The latter measurements reveal a peculiar satellite structure in the Ga 2p core level spectrum, absent at the surface, and a core-level broadening that can be attributed to photoelectron recoil. The photoemission experiments indicate that the energy separation between the valence band and the Fermi level is about 4.4 eV, a valence band maximum at the point and an effective mass of the highest lying bands of -4.2 free electron masses. The value of the bandgap compares well with that obtained by optical experiments and with that obtained by calculations performed using a hybrid density-functional, which also reproduce well the dispersion and density of states.
Japanese Journal of Applied Physics, 2011
The density of states (DOS) and energy band structure of crystalline In-Ga-Zn-O (c-IGZO) and the impact of point defects on its electronic structure are investigated by first-principles calculations based on the density function theory. The calculated DOS showed that the p-orbitals of the oxygen atoms mostly contribute to the valance band maximum (VBM) of c-IGZO. The conduction band minimum (CBM) is dominated by s-orbitals of the Zn/Ga mixture atoms, while the In atoms have the largest spatial spread of wave function. Oxygen vacancies create fully occupied defect states within the band gap and serve as deep donors. Both hydrogen substitutions and interstitials act like shallow donors, and raise the Fermi level above the CBM. Oxygen split interstitials created fully occupied defect states above VBM, while oxygen octahedral interstitials create both occupied and unoccupied states, and may serve as acceptors.
Band Gap and Band Offset of Ga2O3 and (AlxGa1−x)2O3 Alloys
Physical Review Applied
Ga2O3 and (AlxGa1−x)2O3 alloys are promising materials for solar-blind UV photodetectors and high-power transistors. Basic key parameters in the device design, such as band gap variation with alloy composition and band offset between Ga2O3 and (AlxGa1−x)2O3, are yet to be established. Using density functional theory with the HSE hybrid functional, we compute formation enthalpies, band gaps, and band edge positions of (AlxGa1−x)2O3 alloys in the monoclinic (β) and corundum (α) phases. We find the formation enthlapies of (AlxGa1−x)2O3 alloys are significantly lower than of (InxGa1−x)2O3, and that (AlxGa1−x)2O3 with x=0.5 can be considered as an ordered compound AlGaO3 in the monoclinic phase, with Al occupying the octahedral sites and Ga occupying the tetrahedral sites. The band gaps of the alloys range from 4.69 to 7.03 eV for β-(AlxGa1−x)2O3 and from 5.26 to 8.56 eV for α-(AlxGa1−x)2O3. Most of the band offset of the (AlxGa1−x)2O3 alloy arises from the discontinuity in the conduction band. Our results are used to explain the available experimental data, and consequences for designing modulation-doped field effect transistors (MODFETs) based on (AlxGa1−x)2O3/Ga2O3 are discussed.
Energetics and migration of point defects in Ga2O3
Physical Review B, 2005
The results of a theoretical study on the point defects of monoclinic -Ga 2 O 3 are reported here. The point defects considered here are vacancies, interstitials together with dopant ions such as Be, Mg, In, Cr, Si, Ge, Sn, and Zr. Since the low symmetry of the monoclinic lattice does not provide an unambiguous location of interstitial sites and migration paths, we propose a unique way for their identification in terms of the electron density topology. Special attention has also been given to the preference among the lattice and interstitial sites for the impurity defects, and its explanation in terms of structural, electrostatic, and electron density arguments. The calculated results find the most prominent features in the lattice to be the existence of ͑i͒ empty channels along the b direction, and ͑ii͒ atomic layers perpendicular to them. Their interplay governs the stability and mobility of the point defects in -Ga 2 O 3 . The anionic Frenkel pair consisting of the oxygen vacancy and oxygen interstitial is predicted to dominate the defect structure in the lattice. The dopants considered here are likely to be stabilized at the octahedral gallium sites, except for Be +2 , which prefers a tetrahedral gallium site in the lattice. Some of the possible migration paths have been determined, and the pseudoactivation energies for the intrinsic, oxygen-rich, and oxygen-deficient conditions are computed as a function of temperature. It is suggested that tuning the concentration of oxygen can lead to a change in the anisotropy of the ionic conductivity in -Ga 2 O 3 .
Physical Review B, 2006
We report the results of a comprehensive study on the structural, electronic, and optical properties of Ga 2 O 3 in its ambient, monoclinic ͑͒ and high-pressure, hexagonal ͑␣͒ phases in the framework of all-electron density functional theory. In both phases, the conduction band minimum is at the zone center while the valance band maximum is rather flat in the k space. The calculated electron effective mass m e * / m 0 comes out to be 0.342 and 0.276 for -Ga 2 O 3 and ␣-Ga 2 O 3 , respectively. The dynamic dielectric function, reflectance, and energy-loss function for both phases are reported for a wide energy range of 0 -50 eV. The subtle differences in electronic and optical properties can be attributed to the higher symmetry, coordination number of Ga atoms, and packing density in ␣-Ga 2 O 3 relative to that in -Ga 2 O 3 .
Surface morphology and electronic structure of bulk single crystal β-Ga[sub 2]Osub 3
Applied Physics Letters, 2009
Experimental studies of the surface morphology and electronic structure of bulk single crystals of the transparent and wide gap semiconductor gallium oxide ͑-Ga 2 O 3 ͒ have been conducted using scanning tunneling microscopy ͑STM͒, low-energy electron diffraction ͑LEED͒, and angle-resolved photoemission spectroscopy ͑ARPES͒. Atomically resolved STM and LEED results for the -Ga 2 O 3 ͑100͒ surface clarify that the predominant surface termination contains both gallium and oxygen, and this surface does not exhibit a reconstruction. The valence band structure was obtained with ARPES and shows good agreement with existing theoretical works at the zone center and along the a ء and c ء directions, except that the calculated bandwidth is ϳ7% too small. There is poorer agreement along the b ء direction, where the experimental bands disperse more strongly than the calculations.
( In x Ga 1 − x ) 2 O 3 alloys for transparent electronics
Physical Review B, 2015
In x Ga 1−x) 2 O 3 alloys show promise as transparent conducting oxides. Using hybrid density functional calculations, band gaps, formation enthalpies, and structural parameters are determined for monoclinic and bixbyite crystal structures. In the monoclinic phase the band gap exhibits a linear dependence on alloy concentration, whereas in the bixbyite phase a large band-gap bowing occurs. The calculated formation enthalpies show that the monoclinic structure is favorable for In compositions up to 50% and bixbyite for larger compositions. This is caused by In strongly preferring sixfold oxygen coordination. The formation enthalpy of the 50:50 monoclinic alloy is much lower than the formation enthalpy of the 50:50 bixbyite alloy and also lower than most monoclinic alloys with lower In concentration; these trends are explained in terms of local strain. Consequences for experiment and applications are discussed.