The continuous growth in artificial intelligence and high-performance computing has necessitated the development of efficient optoelectronic artificial synapses crucial for neuromorphic computing (NC). Ga2O3 is an emerging wide-bandgap semiconductor with high deep ultraviolet absorption, tunable persistent photoconductivity, and excellent stability toward electric fields, making it a promising component for optoelectronic artificial synapses. Currently reported Ga2O3 optoelectronic artificial synapses often suffer from complex fabrication processes and potential room for improvement due to plasticity. To address the issue of low device plasticity and practical application scenarios, we present an amorphous Ga2O3 (α-GaOx) flexible optoelectronic artificial synapse. This synapse modulates light stimulus signals using electron/oxygen vacancies and optical stimulation and operates as a visual storage device for information processing. We investigate the improvement of the optoelectronic synapses' plasticity by controlling the number of oxygen vacancies via a plasma treatment method and demonstrate its effective application in a three-layer backpropagation neural network for handwritten digit classification. Under the same stimulus conditions, the synaptic weight of samples treated with Ar plasma exhibits a higher rate of change, with the current levels increasing by 2–3 orders of magnitude, achieving greater plasticity. The improved optoelectronic synapses achieved an accuracy of 93.34%/94%, demonstrating their potential as efficient computing solutions and insights for future applications in NC chips.

We report on the electronic properties of β-(In_xGa_1-x)₂O₃ alloys with different In-content up to 18.75% using density functional theory (DFT) calculations. The effect of In-content on the band structures as well as the crystal structures of β-(In_xGa_1-x)₂O₃ alloys is presented and discussed. Our analysis shows that β-(In_xGa_1-x)₂O₃ alloys exhibits indirect gap property, with the band gap reducing from 4.817 eV to 4.422 eV when the In-content increases up to 18.75%. The bandgap energy corresponds to the wavelength region extending from 255 to 280 nm, which implies the possibility for β-(In_xGa_1-x)₂O₃ alloys to be applied in the deep UV photodetectors. The electron and heavy hole effective masses are also obtained for the first time based on the band edge dispersions of the β-(In_xGa_1-x)₂O₃ materials. Additionally, the effect of band parameters on the impact ionization processes using β-(In_xGa_1-x)₂O₃ materials are analyzed. Our new insight regarding the electronic properties indicate the potential of β-(In_xGa_1-x)₂O₃ alloys in deep ultraviolet photodetector applications.

First-principle density functional theory calculations were performed to explore electronic and structural properties of β -(Al _x In _y Ga _{1− x − y} ) ₂ O ₃ quaternary alloys with both Al-content ( x ) and In-content ( y ) ranging from 0% to 18.75%. The β -(Al _x In _y Ga _{1− x − y} ) ₂ O ₃ quaternary alloys exhibit indirect band gap property with the bandgap energy varying from 4.432 to 5.171 eV. Electron effective masses are also presented for β -(Al _x In _y Ga _{1− x − y} ) ₂ O ₃ quaternary alloys, showing a general reduction with In-content increases but a general increment with Al-content increases in the material. Further analysis indicates the possibility of achieving lattice-matched or near-lattice-matched β -(Al _x In _y Ga _{1− x − y} ) ₂ O ₃ / β -Ga ₂ O ₃ structures system, which is critical for high performance field effect transistor and deep ultraviolet photodetector applications. Our work shows that the β -(AlInGa) ₂ O ₃ alloys with proper tuning of Al- and In-content have strong potential to be used as part of the epitaxial layers for β -Ga ₂ O ₃ -based material system.

Gallium oxide has been attracting much interest due to its tremendous potential for power device application. The (B_xGa_1−x)₂O₃ ternary alloys of monoclinic and orthorhombic phases with the B-content covering the full composition were studied using first-principles density functional theory calculations. The effect of the B-content on the structural and electronic properties of (B_xGa_1−x)₂O₃ alloys is discussed. The formation enthalpy of the ternary alloys has been investigated, indicating the feasibility of synthesizing (B_xGa_1−x)₂O₃ alloys depending on the specified growth temperature condition. In addition, the increase in the B-content in (B_xGa_1−x)₂O₃ alloys generally leads to the decrease in lattice constants, implying possible tensile strain if grown on the Ga₂O₃ substrate. Our analysis on the electronic properties shows that all (B_xGa_1−x)₂O₃ alloys exhibit indirect gap property, in which the bandgap increases from 4.83 eV to 6.86 eV in the monoclinic phase and from 5.32 eV to 11.27 eV in the orthorhombic phase when the B-content increases from 0% to 100%. The band alignment between Ga₂O₃ and B₂O₃ in the (100)-direction is also presented, showing a type-II and type-I alignment for monoclinic-based and orthorhombic-based alloys, respectively. Our results showed an extremely large conduction band offset of 5.76 eV between orthorhombic-based Ga₂O₃ and B₂O₃ alloys. Our studies regarding the electronic and structural properties provide important insight regarding the potential of (B_xGa_1−x)₂O₃ alloys for III-oxide-based electronic and optoelectronic device applications.

In this study, we present an investigation of the spontaneous and piezoelectric polarization in the ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructures using density functional theory calculations. The spontaneous polarization (Psp) was found to increase from 23.93 to 26.34 μC/cm2 when Al-content increase from 0% to 50%. With Al-content increasing, the strain-induced piezoelectric polarization (Ppe) increases, which negates the Psp, causing the total polarization (Ptot) of the epitaxy layer in the AlGaO/GaO heterostructure to remain almost constant across all Al compositions. Additionally, due to the ferroelectric nature of ε-Ga2O3, a high-density polarization-induced two-dimensional electron gas (2DEG) can be formed at the interface of polarization reversed ε-(AlxGa1–x)2O3/ε-Ga2O3 when an electric field is applied. Using the 1D Schrödinger–Poisson model, the 2DEG of polarization reversed ε-(Al0.125Ga0.875)2O3/ε-Ga2O3 was found to be 2.05 × 1014 cm−2, which is nearly ten times larger than that of GaN-based structures. Our work indicates that ε-(AlxGa1–x)2O3/ε-Ga2O3 heterostructure could play a key role attributed to the large polarization and capability in modulating the polarization for high-power electronic and radio frequency device applications.

First-principles density functional theory is applied to investigate the electronic and structural properties of dilute-Se β-Ga₂(O_1−xSe_x)₃ alloys with the Se-content ranging from 0% to 16.67%. The findings showed that the addition of Se has significant effect on the β-Ga₂O₃ alloy properties. The equilibrium volume and lattice parameters of β-Ga₂(O_1−xSe_x)₃ alloys are presented, showing a general expansion with increasing Se-content. Further analysis indicates the expansion rate in the c (001) direction is much larger than that in the a and b directions, in which the information provides important guidance for the manufacturing of the β-Ga₂(O_1−xSe_x)₃/Ga₂O₃-based material. From our analysis of the band structures, the β-Ga₂(O_1−xSe_x)₃ alloys exhibit indirect bandgap property with the bandgap energy decreasing dramatically from 4.868 eV to 2.759 eV. The wavelength derived from the direct bandgap energy covers a regime from 255 nm to 475 nm, implying the potential of β-Ga₂(O_1−xSe_x)₃ alloys in an ultraviolet photodetector and visible light applications. In addition, electron effective masses are calculated and presented for the β-Ga₂(O_1−xSe_x)₃ alloys, in which the electron effective mass reduces as the Se-content increases. As a part of a highly mismatched alloy semiconductor class, dilute-Se Ga₂(O_1−xSe_x)₃ is discussed for the first time with no prior literature in our work, and our findings indicate the potential implementation of GaOSe alloys for electronic and optoelectronic device applications.