383. Modulating electronic properties of β-Ga2O3 by strain engineering

Fig. 1 (a) Optimized strain values and (b) bond lengths of β-Ga2O3 under different strain states: uniaxial, biaxial, and isotropic, which correspond to induced strain values.

Fig. 2 Strain-induced effects on the bandgap of β-Ga2O3 as functions of (a) uniaxial, (b) biaxial, and (c) isotropic strain. The vertical lines indicate the strain point where indirect-to-direct transition occurs.

Fig. 3 Electron effective masses of β-Ga2O3 as functions of (a) uniaxial, (b) biaxial, and (c) isotropic strain and (d) changes on the electron effective mass ratio under each strain state. The dashed line represents the average electron effective mass and mass ratio of strain-free β-Ga2O3.

Ruijia Zhang, et al, Results in Physics 52, 106916 (2023)
https://doi.org/10.1016/j.rinp.2023.106916

(1) Strain manipulation can induce an indirect-direct bandgap transition.
(2) The calculated average bond lengths of Ga1-O and Ga2-O are 1.816 Å and 1.969 Å, respectively.
(3) Achieving large strain in β-Ga2O3 can be challenging due to its relatively high elastic modulus and anisotropic monoclinic crystal structure.
(4) In the case of uniaxial or biaxial strain, the bandgap decreases as tension increases, while regarding compression, the bandgap slightly increases as compression increases within a certain range, and then begins to decrease with further compression. With regard to the isotropic strain, the bandgap evolution is almost linearly reduced as a function of strain.
(5) The impact of isotropic change on the electronic property is stronger compared with the case of uniaxial and biaxial strain.
(6) The underlying mechanism of bandgap evolution in β-Ga2O3 can be attributed to the strain-induced variations in the Ga-O bond length, which ultimately affect the distance between the conduction band and valence band.
(7) The unstrained β-Ga2O3 features an indirect bandgap of 4.91 eV with the CBM at Γ point and the VBM at the Σmax point along the M2-D line.
(8) Establishing a clear relationship between hole effective mass and p-type conductivity remains challenging.
(9) From the k•p perturbation theory, electron effective mass at the Γ point is approximately proportional to the bandgap value. In each strain state, there is an almost linearly decreasing relationship between electron effective mass and strain.