【Member Papers】Surface-Step-Controlled In-Plane Orientation of β-Ga₂O₃ Films on 4H-SiC for Deep-Ultraviolet Photodetectors

      A research team led by Professors Qingwen Song and Yuming Zhang from Xidian University, in collaboration with Professor Lianbi Li from Xi’an Polytechnic University and Professor Jichao Hu from Xi’an University of Technology, published an article in Chemical Engineering Journal entitled “Surface-Step-Controlled In-Plane Orientation of β-Ga₂O₃ Films on 4H-SiC for Deep-Ultraviolet Photodetectors”.

      Gallium oxide (Ga₂O₃), an ultra-wide-bandgap semiconductor with a bandgap of approximately 4.8 eV, has attracted considerable interest for power electronics, deep-ultraviolet (DUV) optoelectronics, and harsh-environment sensing. Its intrinsic solar-blind response makes β-Ga₂O₃ particularly attractive for DUV photodetection without additional optical filters. However, operation at elevated temperatures is often accompanied by increased dark current and degraded signal-to-noise-related performance. Therefore, high-quality β-Ga₂O₃ films with controlled crystallographic orientation and reliable high-temperature photoresponse are essential for advancing DUV photodetectors.

      Heteroepitaxy provides greater flexibility than growth on native β-Ga₂O₃ substrates, and 4H-SiC is a promising platform because of its chemical stability, favorable crystallographic matching, and high thermal conductivity. Although the out-of-plane relationship β-Ga₂O₃ (-201) ∥ 4H-SiC (0001) can be established, the threefold rotational symmetry of the 4H-SiC (0001) surface and the monoclinic structure of β-Ga₂O₃ allow six possible in-plane rotational variants. Their coexistence can lead to multidomain growth, local misorientation, and degraded material quality. Suppressing these competing variants and promoting a dominant in-plane orientation therefore remain key challenges for β-Ga₂O₃/4H-SiC heteroepitaxy.

      This study addresses the formation of multiple in-plane rotational variants during β-Ga₂O₃ heteroepitaxy on 4H-SiC and systematically investigates the effects of substrate off-cut and H₂-induced surface steps on the orientation evolution of the films. β-Ga₂O₃ films were grown on surface-treated 4H-SiC substrates by chemical vapor deposition (CVD), and the effect of substrate off-cut and H₂-induced surface steps on the crystallographic orientation evolution was systematically investigated. By comparing on-axis and 4° off-axis 4H-SiC substrates with and without H₂ etching, together with XRD φ-scan and pole figure measurements, we show that the stepped off-axis surface strongly suppresses competing in-plane rotational variants and promotes the formation of a dominant β-Ga₂O₃ orientation. Density functional theory calculations were used to understand the preferential bonding between β-Ga₂O₃ (-201) and 4H-SiC (0001), providing theoretical support for the observed epitaxial alignment. Based on the optimized films, lateral Pt/β-Ga₂O₃/Pt MSM photodetectors were fabricated, showing a distinguishable DUV photoresponse at 300 °C despite increased dark current at high temperature. An 8 × 8 photodetector array was further demonstrated as a proof-of-concept DUV imaging device. This work provides insight into surface-step-controlled β-Ga₂O₃ heteroepitaxy on 4H-SiC and its application potential for high-temperature DUV imaging and sensing applications.

Highlights

      A four-group comparison using on-axis and off-axis 4H-SiC substrates with and without H₂ etching was established to systematically reveal the role of surface steps in controlling the in-plane orientation of β-Ga₂O₃.

      Surface steps were used to regulate the in-plane nucleation orientation of β-Ga₂O₃, effectively suppressing competing rotational variants during β-Ga₂O₃/4H-SiC heteroepitaxy.

      Structural characterization and density functional theory calculations clarified the epitaxial arrangement of β-Ga₂O₃(-201) ∥4H-SiC (0001) and β-Ga₂O₃ [010] ∥ 4H-SiC [11-20].

      An 8 × 8 array fabricated from the optimized β-Ga₂O₃/4H-SiC film demonstrated proof-of-concept DUV imaging, supporting the feasibility of this material platform for high-temperature array photodetection.

Conclusion

      Here, β-Ga₂O₃ films were grown on 4H-SiC substrates by CVD, and the effects of substrate off-cut and H₂-induced surface steps on the in-plane orientation were systematically investigated. Cross-comparison experiments using on-axis and 4° off-axis 4H-SiC substrates with and without H₂ etching show that the stepped off-axis surface effectively suppresses competing rotational variants. XRD φ-scan and pole figure measurements reveal a transition from six in-plane variants to a dominant orientation with minor 180° rotational variants. As a result, the rocking-curve FWHM decreases from 1.26° to 0.75°, and the RMS roughness is reduced from 12.1 to 1.5 nm. Structural and DFT analyses confirm β-Ga₂O₃ (-201) ∥ 4H-SiC (0001) and β-Ga₂O₃ [010] ∥ 4H-SiC [11-20], with a favorable binding energy of -1.13 eV. The optimized film shows an O_II/(O_I + O_II) ratio of 9.1%. Based on this film, lateral MSM DUV photodetectors exhibit a distinguishable photoresponse at 300 °C, achieving a PDCR of ~5 × 10³ and a responsivity of 24.79 A/W. and an 8 × 8 array demonstrates proof-of-concept DUV imaging.

Project Support

      This work was supported in part by, the National Natural Science Foundation of China under Grant 62404163 and U2330109, the China Postdoctoral Science Foundation under Grant 2024M752516, Key Research and Development Program of Shaanxi Province under Grant 2025GH-YBXM-052 and 2024GX-YBXM-081), Basic Research Program of Natural Science of Shaanxi Province under Grant 2025JC-YBQN-759 and 2024JC-YBMS-023, Shaanxi Province "Scientist + Engineer" Team Building under Grant 2025QCY-KXJ-041), Science and Technology Plan Project of Xi’an under Grant 25GXKJRC00074.