First-Principles Studies for Electronic Structure and Optical Properties of Strontium Doped β-Ga2O3 (original) (raw)
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Atomic-scale characterization of structural and electronic properties of Hf doped β-Ga2O3
Applied Physics Letters
In this letter we investigate the atomic and electronic structure of Hf-doped β-Ga2O3 single crystal using high resolution scanning transmission electron microscopy imaging and electron energy loss spectroscopy. UV-vis-NIR absorption measurements and density functional theory calculations are performed to further connect the nanoscale observation to the macroscale properties arising from the atomic structure. The Hf-doped sample was grown from the melt with a nominal Hf concentration of 0.5%at. We show that the Hf dopants prefer to occupy octahedral over tetrahedral sites by 0.68 eV and have some resistance to form precipitates due to a repulsive interaction of 0.17 eV between Hf atoms on neighboring sites. Also, the presence of Hf atoms on either tetrahedral or octahedral sites do not significantly affect the crystal structure of β-Ga2O3. Finally, the bandgap values of the Hf doped β-Ga2O3 obtained by EELS and UV-Vis-spectroscopy were Eg = 4.83 ± 0.1 eV and 4.75 ± 0.02 eV respectively, similar to the values reported for unintentionally doped β-Ga2O3 crystals. All these results make Hf an excellent dopant candidate for β-Ga2O3. The most thermally stable polymorph of Ga2O3, beta-gallium oxide (-Ga2O3), is an exciting semiconductor that combines an ultrawide bandgap (Eg ~ 4.8 eV) with a reasonable mobility (~ 100 cm 2 /V) and a high breakdown field with a predicted value of 8 MV/cm: properties which makes it a great candidate in high-power electronics, optical devices, and gas sensing detectors [1, 2]. In addition, the flexibility and tunability of its electronic properties, that can be achieved through doping, makes it an extremely promising candidate for future electronic device design [3]. Several dopants for -Ga2O3 have been studied, including Si, Sn, Ge, Ta and Nb, resulting in free-electron densities ranging from 1 x 10 17 to 2 x 10 19 cm-3 and mobilities from 25 to 130 cm 2 /V•s [4, 5, 6, 7, 1, 8]. These dopants thus have been shown to allow tunable ntype conductivity in -Ga2O3 [4, 5, 6, 7, 1], enabling applications like charge-transfer devices and optoelectronic devices. Saleh et al. have recently studied Zr as an alternative dopant and demonstrated tunable n-type conductivity in Zr-doped bulk -Ga2O3 grown from the melt, with
Materials, 2021
Gallium oxide (Ga2O3) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga2O3 is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga2O3 and Ca-doped α-Ga2O3 band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure...
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 .
ECS Journal of Solid State Science and Technology
Undoped and Sn-doped β-Ga2O3 single crystals were grown by optical floating zone technique by varying the doping concentration of Sn from 0.05 wt% to 0.2 wt%. Uniform distribution of the dopant ions was achieved by heat treatment. The crystalline quality and the expansion of the lattice were observed from the PXRD. Raman spectra reveals the incorporation of Sn atoms into the lattice by replacing Ga in the octahedral site. The interplanar distance (d) was calculated as 2.39 Å from the HR-TEM micrographs. The transmittance was found to be decreasing from 80% to 78% as the concentration of Sn increases. The absorption spectra shows a cut off edge around 260 nm for undoped and 270 nm for all Sn doped samples. The bandgap obtained for undoped β-Ga2O3 was 4.36 eV. The doping of 0.05 wt% of Sn decrease the value of bandgap to 4.08 eV, but, for 0.1 wt% and 0.2 wt% Sn an increase in the bandgap value of 4.13 eV and 4.20 eV was observed respectively. The refractive index was found to be 1.96 ...
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.
Electronic and ionic conductivity in β-Ga2O3 single crystals
Journal of Applied Physics
In this work, we quantify electronic and ionic contributions to conductivity in the bulk and depletion widths of back-to-back sputtered Pt Schottky contacts on single crystals of β-Ga2O3. We also demonstrate asymmetric changes to these contacts induced by DC bias at temperatures as low as 200 °C, which has obvious bearing on the performance and reliability of devices. Crystals, which were unintentionally doped, doped with Zr donors, and doped with Mg acceptors, were characterized from room temperature to 900 °C. Electrochemical impedance spectroscopy, current–voltage (IV), capacitance–voltage, and the Wagner DC polarization method were employed to characterize changes in conductivity, doping, and built-in potentials with temperature and bias. This work demonstrates that ionic conductivity can be on-par with electronic conductivity in multiple circumstances in bulk crystal samples and leads to changes in Schottky contacts with an applied bias. While it has not been demonstrated that ...
Editors' Choice—Hydrogen Centers in β-Ga2O3: Infrared Spectroscopy and Density Functional Theory
ECS Journal of Solid State Science and Technology, 2019
β-Ga 2 O 3 is a transparent conducting oxide with a wide bandgap (4.9 eV) whose properties are generating widespread interest. It has been found that hydrogen can play a key role in the conductivity of Ga 2 O 3 by passivating deep defects and acting as a shallow donor. Recent vibrational spectroscopy experiments have found a dominant hydrogen center with a polarized O-H line at 3437 cm −1. These experiments along with theoretical analysis assign this line to a defect consisting of two equivalent H atoms trapped at a relaxed Ga vacancy. An expansion of this research has involved annealing treatments as well as measurements at different crystal orientations. These results have discovered a reservoir of "hidden" hydrogen in Ga 2 O 3 whose identification involves a variety of hydrogen centers associated with the Ga vacancy, as well as other possible species.
Zenodo (CERN European Organization for Nuclear Research), 2022
In this research we have investigated systematically, the structural, electronic, bonding, optical, thermodynamic aspects of the GaAgO2 crystal using first-principles computations based on the density functional theory (DFT). To begin, the bandgap energies of GaAgO2 crystal have estimated to be 0.640 eV and 0.768 eV using the Generalized Gradient Approximation (GGA) based on the Perdew-Burke-Ernzerhof (PBE) and Revised Perdew-Burke-Ernzerhof (RPBE) functional methods. The density of state and partial density of state of GaAgO2 were then simulated to determine the nature of the orbital of the Ga, Ag, and O atoms. The Mulliken population charge and electron density distributions have estimated to further elucidate the bonding nature of GaAgO2. The complex dielectric function, refractive index, reflectivity, absorption coefficient, loss function, and photoconductivity of GaAgO2 are all computed and analyzed in depth for the optical transitions. Additionally, come to the realization of it, the thermo-electronic and thermophysical features have been added to enable this crystal to absorb visible light and retain a stable thermal state, enabling them to be employed in optoelectronic devices such as lasers, solar cells, and even luminescence ones.
Journal of Applied Physics, 2019
We characterized unintentionally doped β-(Al0.19Ga0.81)2O3 for its structural, band, and electrical properties by using a variety of material and electrical characterization methods such as atom probe tomography (APT), transmission electron microscope, X-ray photoelectron spectroscopy (XPS), capacitance-voltage measurement, and a temperature dependent forward current-voltage measurement. A 115 nm thick β-(Al0.19Ga0.81)2O3 film was grown by molecular beam epitaxy on Sn doped Ga2O3 substrates. Reciprocal space mapping shows a lattice matched (Al0.19Ga0.81)2O3 layer. Both APT and TEM results confirm a sharp β-(Al0.19Ga0.81)2O3/β-Ga2O3 interface. XPS measurements show conduction band offsets of 2.78 ± 0.25 eV and 0.79 ± 0.25 eV between the SiO2/β-(Al0.19Ga0.81)2O3 and β-(Al0.19Ga0.81)2O3/β-Ga2O3 interfaces, respectively. Extracted room temperature Schottky Barrier Heights (SBHs) after zero field correction for Pt, Ni, and Ti were 2.98 ± 0.25 eV, 2.81 ± 0.25 eV, and 1.81 ± 0.25 eV, respe...