Scalable Solar-Blind Imaging Enabled by Single-Crystalline Beta-Ga2O3 Membranes on Silicon Backplanes

Ultrawide-bandgap semiconductors are attractive for solar-blind ultraviolet (UV) detection owing to their intrinsically low noise and high spectral selectivity, yet their deployment in large-area, high-density electronic imaging systems remains limited by a fundamental trade-off between material quality, device speed, and compatibility with high-density planar silicon readout circuits. Here, we report a membrane-enabled integration platform based on transferable single-crystalline beta-Ga2O3 that overcomes these constraints at the system level. By exploiting the weak interplanar bonding of beta-Ga2O3 (100) plane, we obtain wafer-scale freestanding single-crystalline membranes that enable vertically integrated photodiodes with sub-microsecond, non-persistent photoresponse and high UV-visible rejection. Crucially, we introduce a stitching-based membrane assembly strategy that decouples array resolution from the size of the source single-crystalline substrate, allowing high-resolution photodetector arrays to be integrated onto silicon thin-film-transistor backplanes. The modular assembled active-matrix UV imaging arrays exhibit uniform solar-blind response without image lag, in stark contrast to arrays based on amorphous or polycrystalline films. Beyond beta-Ga2O3, this membrane-enabled and stitching-based modular integration strategy provides a general route toward high-speed, high-resolution electronic imaging systems using transferable single-crystalline semiconductors.

💡 Research Summary

This paper presents a comprehensive integration platform that leverages the intrinsic advantages of the ultra‑wide‑bandgap semiconductor β‑Ga₂O₃ for solar‑blind ultraviolet (UV) imaging while simultaneously addressing the long‑standing trade‑off among material quality, device speed, and compatibility with high‑density silicon readout circuits. The authors exploit the weak interplanar bonding of the (100) plane of β‑Ga₂O₃ to fabricate wafer‑scale, freestanding single‑crystalline membranes. The process begins with homoepitaxial growth of β‑Ga₂O₃ on a β‑Ga₂O₃ (100) substrate, followed by deposition of a Ti/Cu metal stressor layer. By carefully tuning the intrinsic stress in this metal stack, the epitaxial film can be cleanly exfoliated using a thermal‑release tape, yielding continuous membranes with well‑defined thickness (as thin as 200 nm) across a 2‑inch wafer.

Structural characterisation (RHEED, EBSD, HAADF‑STEM, XRD) confirms that the membranes retain single‑crystal order, are twin‑free, and exhibit an atomically sharp interface with the substrate. X‑ray photoelectron spectroscopy shows a sharp O 1s peak, indicating high chemical purity, while UV‑visible absorption reveals a direct bandgap of ~4.89 eV and an absorption coefficient >1.5 × 10⁵ cm⁻¹ in the deep‑UV, enabling >98 % absorption at 254 nm for a 200 nm film. Femtosecond pump–probe measurements demonstrate rapid carrier relaxation (τ ≈ 328 ps) and the absence of long‑lived trap‑related components, in stark contrast to amorphous Ga₂O₃ (τ ≈ 1.69 ns).

The membranes are employed to fabricate vertical photodiodes: a semi‑transparent Pt top electrode and a Ti/Cu bottom electrode sandwich the β‑Ga₂O₃ layer, forcing carrier transport across the film thickness. Devices exhibit dark currents in the picoampere range, a responsivity of ~10⁶ A W⁻¹ at 254 nm, and sub‑microsecond response times (≈0.8 µs). Crucially, the photoresponse is non‑persistent; repeated pulsed illumination shows no image lag, a major limitation of devices based on amorphous or polycrystalline wide‑bandgap films.

To scale the technology to high‑resolution imaging arrays, the authors introduce a stitching‑based membrane assembly method. Small membrane tiles are precisely positioned and bonded onto a silicon thin‑film‑transistor (TFT) backplane, decoupling array resolution from the size of the original crystal. This approach allows thousands of sub‑10 µm pixels to be assembled from a single 2‑inch crystal, enabling dense active‑matrix UV imagers that are fully compatible with standard CMOS/TFT processing.

System‑level testing of the assembled active‑matrix arrays demonstrates uniform solar‑blind response (cut‑off ≈280 nm) with negligible visible‑light sensitivity, pixel‑to‑pixel uniformity, and, most importantly, the complete absence of image lag during video capture. Compared with conventional amorphous or polycrystalline Ga₂O₃ arrays, the single‑crystalline β‑Ga₂O₃ devices deliver superior temporal resolution, lower noise, and higher spectral selectivity.

In summary, the work delivers three pivotal advances: (1) a wafer‑scale, transfer‑ready single‑crystalline β‑Ga₂O₃ membrane fabrication technique; (2) vertically integrated photodiodes that achieve sub‑microsecond, non‑persistent solar‑blind detection; and (3) a modular stitching strategy that enables high‑resolution active‑matrix integration on silicon TFT backplanes. The authors argue that this membrane‑enabled, stitching‑based paradigm is broadly applicable to other ultra‑wide‑bandgap single‑crystalline materials (e.g., AlN, BN), opening a pathway toward next‑generation high‑speed, high‑resolution imaging systems for applications ranging from space‑based UV astronomy to secure optical communication and real‑time industrial UV monitoring.