We demonstrated high responsivity metal–semiconductor–metal (MSM) solar-blind photodetectors by integrating exfoliated β-Ga2O3 microlayers with graphene, which is a deep ultraviolet (UV) transparent and conductive electrode. Photodetectors with MSM structures commonly suffer from low responsivity, although they feature a facile fabrication process, low dark current, and fast response speed. The β-Ga2O3 MSM solar-blind photodetectors with graphene electrodes exhibited excellent operating characteristics including higher responsivity (∼29.8 A/W), photo-to-dark current ratio (∼1 × 106%), rejection ratio (R 254nm/R 365nm, ∼9.4 × 103), detectivity (∼1 × 1012 Jones), and operating speed to UV-C wavelengths, compared with MSM photodetectors with conventional metal electrodes. Absence of shading by the integration of graphene with β-Ga2O3 allows maximum exposure to the incident photons, suggesting a great potential for deep UV optoelectronic applications.

This study demonstrated the exfoliation of a two-dimensional (2D) β-Ga2O3 nano-belt and subsequent processing into a thin film transistor structure. This mechanical exfoliation and transfer method produces β-Ga2O3 nano-belts with a pristine surface as well as a continuous defect-free interface with the SiO2/Si substrate. This β-Ga2O3 nano-belt based transistor displayed an on/off ratio that increased from approximately 10(4) to 10(7) over the operating temperature range of 20 °C to 250 °C. No electrical breakdown was observed in our measurements up to VDS = +40 V and VGS = -60 V between 25 °C and 250 °C. Additionally, the electrical characteristics were not degraded after a month-long storage in ambient air. The demonstration of high-temperature/high-voltage operation of quasi-2D β-Ga2O3 nano-belts contrasts with traditional 2D materials such as transition metal dichalcogenides that intrinsically have limited temperature and power operational envelopes owing to their narrow bandgap. This work motivates the application of 2D β-Ga2O3 to high power nano-electronic devices for harsh environments such as high temperature chemical sensors and photodetectors as well as the miniaturization of power circuits and cooling systems in nano-electronics.

We report on air stable planar micro-supercapacitors (MSCs) using a non-aqueous solvent based gel electrolyte and stable performance of encapsulated MSC array under stretching and exposure to water.

We fabricated solar-blind photodetectors based on exfoliated two-dimensional β-Ga2O3 flakes, and then systematically characterized their photoresponsive properties. They exhibit extraordinary photoresponsive properties including the highest responsivity among reported semiconductor thin-film solar-blind photodetectors.

Field effect transistors (FETs) using SiO2 and Al2O3 as the gate oxides for the back and front sides, respectively, were fabricated on exfoliated two-dimensional (2D) β-Ga2O3 nano-belts transferred to a SiO2/Si substrate. The mechanical exfoliation and transfer process produced nano-belts with smooth surface morphologies and a uniform low defect density interface with the SiO2/Si substrate. The depletion mode nanobelt transistors exhibited better channel modulation with both front and back gates operational compared to either front or back-gating alone. The maximum transconductance was ∼4.4 mS mm−1 with front and back-gating and ∼3.7 mS mm−1 with front-gating only and a maximum drain source current density of 60 mA mm−1 was achieved at a drain-source voltage of 10 V. The FETs had on/off ratios of ∼105 at 25 °C with gate-source current densities of ∼2 × 10−3 mA mm−1 at a gate voltage of −30 V. The device characteristics were stable over more than a month for storage in air ambient and the results show the potential of 2D β-Ga2O3 for power nanoelectronics.

Semiconductor materials ideal for solar-blind photodetectors (PDs) require an ultra-wide and direct bandgap to detect UV-C spectral wavelengths effectively. Using the mechanically exfoliated high-quality β-Ga2O3 micro-flakes that have a direct bandgap of ∼4.8 eV, we fabricated solar-blind PDs with a metal-semiconductor-metal (MSM) structure that can reduce the dark current, and then systemically investigated their photoresponse properties. The MSM devices with two Ni/Au Schottky contacts exhibited an extremely low dark current and high sensitivity (ratio of photocurrent to dark current > 103) in UV-C wavelengths. In addition, they exhibited fast and stable on/off characteristics and high responsivity (1.68 A/W), with a superior rejection ratio when compared with the reported thin-film MSM solar-blind PDs, indicating the high potential of the quasi-two-dimensional β-Ga2O3 for optoelectronic applications.

β-Ga(2)O(3) films grown on Al(2)O(3) by a metalorganic chemical vapor deposition technique were used to fabricate a solar-blind photodetector with a planar photoconductor structure. The crystal structure and quality of the β-Ga(2)O(3) films were analyzed using X-ray diffraction and micro-Raman spectroscopy. Si ions were introduced into the β-Ga(2)O(3) thin films by ion implantation method and activated by an annealing process to form an Ohmic contact between the Ti/Au electrode and the β-Ga(2)O(3) film. The electrical conductivity of the β-Ga(2)O(3) films was greatly improved by the implantation and subsequent activation of the Si ions. The photoresponse properties of the photodetectors were investigated by analyzing the current-voltage characteristics and the time-dependent photoresponse curves. The fabricated solar-blind photodetectors exhibited photoresponse to 254 nm wavelength, and blindness to 365 nm light, with a high spectral selectivity.

We demonstrated the thinning of exfoliated quasi-two-dimensional b-Ga 2 O 3 flakes by using a reactive ion etching technique. Mechanical exfoliation of the bulk b-Ga 2 O 3 by using an adhesive tape was followed by plasma etching to tune its thickness. Since b-Ga 2 O 3 is not a van der Waals material, it is challenging to obtain ultra-thin flakes below a thickness of 100 nm. In this study, an etch rate of approximately 16 nm/min was achieved at a power of 200 W with a flow of 50 sccm of SF 6 , and under these conditions, thinning of b-Ga 2 O 3 flakes from 300 nm down to $60 nm was achieved with smooth morphology. We believe that the reaction between SF 6 and Ga 2 O 3 results in oxygen and volatile oxygen fluoride compounds, and non-volatile compounds such as GaF X that can be removed by ion bombardment. The opto-electrical properties were also characterized by fabricating solar-blind photodetectors using the plasma-thinned b-Ga 2 O 3 flakes; these detectors showed fast response and decay with excellent responsivity and selectivity. Our results pave the way for tuning the thickness of two-dimensional materials by using this scalable, industry-compatible dry etching technique.