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Amorphous gallium oxide (a-GaOx) exhibits excellent electrical conductivity, a wide bandgap, high breakdown field strength, high visible light transmittance, high sensitivity to specific ultraviolet wavelengths, low preparation temperatures, relatively simple processing, wide substrate applicability, and ease of obtaining high-quality thin films. These attributes make it a suitable candidate for applications in transparent electronic devices, ultraviolet detectors, high-power devices, and gas sensors. Presently, the research on a-GaOx remains limited, focusing primarily on films with an O/Ga ratio less than or equal to 1.5. Increasing the concentration of oxygen vacancies to enhance the conductivity of the material often leads to a reduction in its bandgap, which is undesirable for high-power applications. Variations in O/Ga in the films can affect the formation of chemical bonds and significantly influence the band structure. In this study, five groups of a-GaOx thin films with high oxygen-to-gallium ratios are successfully fabricated by increasing the gas flow rate at low sputtering power. The elemental compositions of the films are analyzed using energy dispersive spectroscopy (EDS), revealing the O/Ga ratio gradually decreasing from 3.89 to 3.39. Phase analysis by using X-ray Diffraction (XRD) confirms the amorphous nature of the films. Optical properties are characterized using an ultraviolet-visible spectrophotometer (UV-Vis), indicating that the optical bandgap and the density of localized states gradually increase. X-ray photoelectron spectroscopy (XPS) is utilized to analyze the elemental compositions, chemical states, and valence band structures of the films, showing that the valence band maximum decreases and the content of Ga2O within the material increases. Subsequently, Au/a-Ga2Ox/Ti/Au Schottky devices are fabricated under the same processing conditions. The I-V characteristics of these devices are measured using a Keithley 4200, revealing changes in the electron transport mechanism at the metal-semiconductor (MS) interface, with the gradual increase in electron affinity calculated. C-V characteristics are measured using a Keithley 590, and the donor concentration (density of localized states) at the interface is calculated to gradually increase. In summary, by controlling appropriate process parameters, it is possible to improve the conductivity of electronic devices while increasing the bandgap of a-GaOx, which is significant for high-power applications.
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Keywords:
- amorphous gallium oxide /
- O/Ga ratio /
- band structure /
- electron transport mechanism
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图 1 a-GaOx薄膜X射线衍射图谱
Figure 1. X-ray diffraction pattern of a-GaOx thin film.
图 2 (a) a-GaOx薄膜的紫外-可见光吸收率曲线; (b) a-GaOx薄膜的$ hv{\text{ - }}{\left( {\alpha hv} \right)^2} $关系曲线; (c) a-GaOx薄膜的$ \ln \alpha {\text{ - }}hv $关系曲线
Figure 2. (a) Ultraviolet-visible light absorption curve of a-GaOx thin film; (b) the $ hv{\text{ - }}{\left( {\alpha hv} \right)^2} $ relationship curve of a-GaOx thin film; (c) the $ \ln \alpha {\text{ - }}hv $ relationship curve of a-GaOx thin film.
图 3 (a) a-GaOx薄膜的XPS价带谱; (b) a-GaOx薄膜的价带顶能量值
Figure 3. (a) XPS valence band spectrum of a-GaOx thin films; (b) the valence of a-GaOx film with the maximum energy value.
图 4 (a)—(e) a-GaOx薄膜O 1s的XPS图谱; (f)—(j) a-GaOx薄膜Ga 3d XPS图谱
Figure 4. (a)–(e) O 1s XPS spectra of a-GaOx thin film; (f)–(j) Ga 3d XPS spectra of a-GaOx thin film.
图 5 a-GaOx Schottky器件 (a)结构图; (b) J-V特性曲线; (c) lnJ-V特性曲线; (d) 1/C2-V特性曲线
Figure 5. a-GaOx Schottky device: (a) Structure; (b) J-V curves; (c) lnJ-V curves; (d) 1/C2-V curves.
图 6 Au/a-GaOx界面处能带结构示意图
Figure 6. Schematic diagram of the band structure at the Au/a-GaOx interface.
图 7 (a) TLM结构示意图; (b) a-GaOx的 Rtatal -L关系图
Figure 7. (a) Schematic diagram of TLM structure; (b) diagrams Rtatal -L of a-GaOx.
表 1 a-GaOx中各元素原子百分比与O/Ga比
Table 1. Percentage of atoms of each element and O/Ga ratio in a-GaOx.
样品 O/％ Ga/％ Si/％ O/Ga比 氧气流量/(cm3·min–1) N1 79.31 20.37 0.32 3.89 0 N2 77.33 21.19 1.48 3.64 2 N3 77.11 21.57 1.32 3.57 3 N4 77.37 21.73 0.91 3.56 4 N5 76.60 22.57 0.83 3.39 5 
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表 2 a-GaOx的Eg与EU
Table 2. Eg and EU of a-GaOx.
样品 N1 N2 N3 N4 N5 Eg /eV 5.200 5.237 5.271 5.277 5.282 EU/eV 0.337 0.349 0.408 0.411 0.422 O/Ga比 3.89 3.64 3.57 3.56 3.39 氧气流量/(cm3·min–1) 0 2 3 4 5
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表 3 a-GaOx的氧空位浓度与Ga1+浓度
Table 3. Oxygen Vacancy Concentration and Ga1+ Concentration in a-GaOx.
样品 S1 S2 S3 S4 S5 O/Ga比 3.89 3.64 3.57 3.56 3.39 氧空位浓度/％ 36 35 38 40 38 Ga1+浓度/％ 58 62 67 68 76
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表 4 Au/a-GaOx界面的理想因子n与势垒$ {\varphi _{{\text{Bn}}}} $
Table 4. Ideal factors n and potential barriers $ {\varphi _{{\text{Bn}}}} $ of Au/ a-GaOx interface.
样品 S1 S2 S3 S4 S5 n 1.663 1.397 1.041 1.395 0.923 $ {\varphi _{{\text{Bn}}}} $/V 0.867 0.866 0.812 0.803 0.797 $ q\chi $/eV 4.233 4.234 4.288 4.297 4.303 $ {R_{{\text{on, sp}}}} $ /(Ω·cm2) 1483 413 332 305 208
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表 5 a-GaOx的TLM结构的接触电阻率rc与片电阻Rsheet
Table 5. Contact resistivity rc and chip resistance Rsheet of the TLM structure of a-GaOx.
样品 M1 M2 M3 M4 M5 rc/(Ω·mm) 2.63×109 2.71×109 2.17×109 2.08×109 1.70×109 Rsheet/
(Ω·□–1)1.33×1010 7.94×109 5.94×109 4.16×109 3.39×109
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