Nanogaps Formation and Recovery Process of Flexible β-Ga2O3 Nanomembranes Under Uniaxial Strain

Abstract

Abstract Body: Ultra-wide-bandgap semiconductors (UWBG's) are a very promising material for the next-generation power semiconductors devices due to the rapid developments and requirements of highly efficient power electronics. The beta phase of Ga2O3 (β-Ga2O3) is considered in a family of UWBG semiconductors, which provides a new opportunity in myriad applications in electronics, optoelectronics, and photonics, with a superior performance matrix than conventional WBG materials. It exhibits some remarkable properties such as ultra-wide bandgap (>4.8 eV) at room temperature, thermally and chemically stability, high carrier mobility (>300 cm2/v.s), critical electric breakdown filed (~8 MV/cm), highest electron-Baliga’s Figure of Merit (BFoM). All of these properties could lead β-Ga2O3, a potential candidate for high-frequency devices, deep-ultraviolet optoelectronics, and high-power applications. However, the monoclinic and anisotropic crystal structure of β-Ga2O3 (a= 12.214 Å, b= 3.037 Å, and c=5.798 Å) exhibits larger lattice constant on the a-axis other than b-axes and c-axes. These benefits could open up a new direction of creating a nanoscale freestanding form of sub-micron thick β-Ga2O3 flake (typically known as nanomembranes, NMs), Recently several research groups have demonstrated creating NMs using the “Scotch tape” method. Thus, β-Ga2O3 provides a new opportunity to realize the use of UWBG’s in flexible devices that have the advantages of high breakdown electric field, transparency and solar blind photodetection while maintaining good mechanical stability. In fact, our group demonstrated the first flexible electronics (Schottky barrier diode and Solar blind photodetector) based on β-Ga2O3 NMs. However, structural-property relationship investigation of β-Ga2O3 NMs under mechanical strain conditions has not been well studied yet. Here in this presentation, we will first discuss the formation of nanogaps β-Ga2O3 NMs under uniaxial strain conditions, and the impact of randomly generated nanogaps on the electrical and optical properties using the β-Ga2O3 NMs fabricated on a plastic substrate. The scanning electron microscope (SEM) and the atomic force microscope (AFM) was used to identify the strain-induced nano-cracks, which also provided direct evidence of layer delamination and fracture in the β-Ga2O3 NMs. It was noticed that the electrical properties of β-Ga2O3 NM, such as the sheet resistance and capacitance were changed under uniaxial strain conditions. In order to investigate the change in sheet resistance and capacitance, a transmission line measurement (TLM) pattern was used. The results uncovered a significant degradation in the electrical properties and uneven distribution of the charges in the β-Ga2O3 NMs. The sheet resistance increased, and the total capacitance decreased due to substantial degradation of β-Ga2O3 NM’s under bending conditions. The optical properties of flexible β-Ga2O3 NMs were also investigated as a solar-blind photodetector. Interestingly, the degraded performance in β-Ga2O3 NM was recovered by employing a water vapor treatment. The presence of OH bonds in β-Ga2O3 NM confirmed by X-ray photoelectron spectroscopy (XPS) indicated that a water vapor treatment chemically bonds the nano-cracks effectively. Hence 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-Ga2O3 NM from multiple bending cycles, thus providing good reliability. This result provides a viable route in realizing high-performance flexible devices, which is one of the crucial components in the upcoming internet of things era.