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Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga2O3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga2O3 thin films using the water-soluble perovskite Sr3Al2O6 as a sacrificial buffer layer. The obtained Ga2O3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga2O3 solar-blind UV photodetector was fabricated by transferring the free-standing Ga2O3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga2O3 photodetector were not sensitive to bending of the device. The free-standing Ga2O3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.
Ga2O3, with a wide band gap of 4.2–5.3 eV, exhibits large breakdown field, high dielectric constant and Baligaʼs figure of merit.[1–4] Meanwhile, Ga2O3 can work steadily in extreme environment, such as high temperature, high electric field, and high energy radiation. Ga2O3 with such properties has a wide range of potential applications in high-power electronic devices, deep ultraviolet (DUV) solar-blind photodetectors, gas sensors, and transparent electrodes on optoelectronic devices.[5–13] Ga2O3 Schottky barrier diodes have a high breakdown voltage.[14] The β-Ga2O3 field-effect transistors (FETs) exhibits a large on/off current rations (
Bendable, lightweight, flexible, sensitive, and wearable, electronic devices are urgently needed in emerging technological applications.[21–24] Flexible and transparent two-dimensional (2D) materials have been employed and developed in electronic technologies, including wearable energy-harvesting systems, folding electronic devices, curved screen electronic devices, soft portable devices, and rollup displays flexible Ga2O3 thin film photodetectors.[17] The Ga2O3 thin film layer deposited directly on the flexible polymer materials was non-crystalline, and the amorphous films were unstable for long-term device applications.[25–30] The Ga2O3 thin film layer can be fabricated by integrating exfoliated Ga2O3 micro-layers,[31] but the thicknesses and dimensions of the Ga2O3 film layer were uncontrollable with the mechanical exfoliation method. In addition, the edge of the film is not intact.
In this paper, a millimeter sized (5 mm ×8 mm) free-standing Ga2O3 thin film was synthesized, and the flexible Ga2O3 solar-blind UV photodetector was fabricated. The Ga2O3 thin film layer transferred to the flexible substrates in this research was crystalline and its thickness was controllable. In addition, the edge of the film was intact. The experimental results demonstrated that the bending of the film had no obvious influence on its electrical performance. This provides an effective transfer method to fabricate crystalline Ga2O3 thin film onto flexible substrates for applications in flexible and wearable electronics.
The SAO buffer layer (BL) was deposited on silicon substrates by radio frequency (RF) magnetron sputtering, and then Ga2O3 thin film was grown on the SAO BL. The base pressure in chamber was 1×10−4 Pa, and the distance between SAO target (99.99% purity) and substrates was 6 cm. The substrates temperatures were 750 °C. The Sr3Al2O6 (SAO)[32,33] BL was deposited under a working pressure of 0.4 Pa and RF power of 120 W. The Ga2O3 thin film was deposited under a working pressure of 0.8 Pa and RF power of 70 W. Then the Ga2O3/SAO bilayer thin films on the Si substrates was immersed into deionized water. The crystal Ga2O3 thin film separated from substrates when SAO film was etched in water.[31,33] Finally, the free-standing Ga2O3 thin film was transferred to the flexible substrates polyethylene terephthalate (PET). The crystal structure of the as-grown film was investigated by transmission electron microscopy (TEM). UV-visible (UV-vis) absorption spectrum was taken using Hitachi U-3900 UV-vis spectrophotometer. The current–voltage (I–V) of the Ga2O3 film-based detectors were measured by Keithely 2450 source meter. To test the electric properties of the flexible Ga2O3 film, interdigital Ti/Au electrodes were deposited on the film by radio frequency magnetron sputtering using shadow mask. The electrode fingers of shadow mask were
Figure
Figure
To investigate photoelectric properties of the film, flexible Ga2O3 based solar-blind UV photodetector was fabricated and a three-pair interdigital Ti/Au electrodes were deposited on top of the β-Ga2O3 thin film to construct a MSM structure device. The thickness of Ti layer and Au layer were 30 nm and 100 nm, respectively. The electrode fingers were
Figure
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In summary, a free-standing Ga2O3 thin film has been fabricated using Sr3Al2O6 as a sacrificial layer. The free-standing Ga2O3 thin film was polycrystalline, thickness was controllable, and the film edge was intact. Additionally, the photoelectric performances testing of the flexible Ga2O3 photodetector showed that the free-standing Ga2O3 thin film had a similar electrical performance whether bending or not, meaning no degradation after bending. The experimental results demonstrated that it was a practical way to fabricate free-standing Ga2O3 thin films by using Sr3Al2O6 as a sacrificial layer. The free-standing Ga2O3 film can be used to fabricate flexible and wearable electronic devices by transferring it to flexible substrates for application.
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