Beta phase gallium oxide (β-Ga~2~O~3~) is a next-generation ultra-wide bandgap semiconductor material that has been drawing tremendous attention for future electronic and optoelectronic applications due to its’ attractive material properties such as ultra-wide bandgap (>4.8 eV) at room temperature, good chemical stability, high carrier mobility (>300 cm^2^/V.s), and a high critical electric breakdown field (\~8 MV/cm). These properties could enable the development of various electronics and optoelectronic devices such as high-power transistors and deep ultra-violet (UV) solar-blind photodetectors. Recently, a nanoscale freestanding form of β-Ga~2~O~3~, called β-Ga~2~O~3~ nanomembranes (NMs), was developed by several groups including our group using the well-known “Scotch-tape” method. The creation of β-Ga~2~O~3~ NMs uses an anisotropic monoclinic crystal structure of β-Ga2O3 that has a larger lattice constant on the a-axis than the other two axes (a= 12.214 Å, b= 3.037 Å, and c=5.798 Å). Thus, β-Ga~2~O~3~ NMs could open up the new possibilities to realize new types of flexible devices that have the advantages of ultra-wide bandgap semiconductors, such as a high breakdown electric field, transparency, and solar-blind photodetection, while still maintaining good mechanical flexibility. However, electrical properties of β-Ga~2~O~3~ under mechanical strain conditions and the demonstration of flexible devices have not well studied yet.

              In this presentation, we will first discuss the relationship of the structure and properties of β-Ga~2~O~3~ NMs under uniaxial strain conditions and the impact on the electrical properties using the β-Ga~2~O~3~ NMs fabricated on a plastic substrate. Strain-induced nano-cracks were observed in β-Ga~2~O~3~ NMs by scanning electron microscope (SEM) and atomic force microscope (AFM), which provided direct evidence of layer delamination and fracture in the β-Ga~2~O~3~ NMs. The changes in electrical properties such as the sheet resistance and capacitance were also investigated under uniaxial strain conditions using a transmission line measurement (TLM) pattern. The results revealed a substantial degradation in the electrical properties and uneven distribution of the charges in the β-Ga~2~O~3~ NMs. Interestingly, the degraded performance in β-Ga~2~O~3~ NM was recovered by employing a water vapor treatment. The presence of OH bonds in β-Ga~2~O~3~ NM confirmed by X-ray photoelectron spectroscopy (XPS) indicated that a water vapor treatment chemically bonds the nano-cracks effectively, so it was possible to recover up to 90 % of the original electrical properties. In addition, the water vapor treatment prevented further performance degradation in β-Ga~2~O~3~ NM from multiple bending cycles, thus providing good reliability. Based on this observation, we then fabricated β-Ga~2~O~3~ NM-based flexible solar-blind photodetectors using a micro-transfer printing technique. The flexible β-Ga~2~O~3~ NMs photodetectors exhibit excellent solar-blind property under the UV illumination. This result provides a viable route in the realization of high performance flexible solar-blind photo-detection systems, which is one of the indispensable and important components in the upcoming internet of things era.


Structure-Property Relationship Investigation of \u03b2-Ga2O3 Nanomembranes Toward Flexible Solar Blind Photodetectors

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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