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Self-powered solar-blind ultraviolet photodetectors are considered for potential applications in secure communication and space detection. However, high-quality p-type wide bandgap semiconductors are nonexistent due to the self-compensation effect, which makes the design of p-n homojunction photodetectors a challenging proposition to date. In this work, a self-powered solar-blind ultraviolet photodetector is fabricated and discussed, based on a novel heterojunction of (InxGa1−x)2O3 ternary alloy films with two different compositions, which has a flexible design and can be easily fabricated for different applications. The heterojunction consists of an amorphous (In0.23Ga0.77)2O3 on the top of a bixbyite (In0.67Ga0.33)2O3 film prepared by radio frequency magnetron sputtering. The amorphous (In0.23Ga0.77)2O3/bixbyite (In0.67Ga0.33)2O3 heterojunction photodetector exhibits a responsivity of 5.78 mA/W, a detectivity of 1.69 × 1011 cm Hz1/2 W−1, and a high solar-blind UV (248 nm)/visible light (450 nm) rejection ratio of 1.39 × 103 at zero bias, suggesting decent spectral selectivity and high performance. The responsivity and peak wavelength of this photodetector can be tuned by the film thickness of the amorphous (In0.23Ga0.77)2O3. This work provides a new design for self-powered solar-blind UV detectors based on ternary alloy heterojunctions. [ABSTRACT FROM AUTHOR]

A two-dimensional electron gas (2DEG) was formed at the interface of an ultrathin ZnO/Ga2O3 heterostructure deposited by atomic layer deposition (ALD) at 200 °C on a SiO2/Si substrate. It is found that the sheet resistance decreases steeply to ∼104 Ω/□ as the thickness of the ZnO layer increases to a certain extent, and an optimal thickness of the top layer is determined. An ∼50-nm-thick β-phase Ga2O3 layer was formed after annealing at 800 °C, and a 12-nm-thick amorphous ZnO layer was observed by x-ray diffraction and transmission electron microscopy. The oxygen defects were analyzed by x-ray photoelectron spectroscopy. The defect energy levels of oxygen vacancies in Ga2O3 and ZnO thin films were calculated by first-principles simulation, and oxygen vacancies were generated at the interface of the ZnO/Ga2O3 thin film heterostructure to form 2DEG, which is demonstrated experimentally and theoretically. An assumption is proposed that the oxygen vacancy plays a role of the donor of free electrons at the ZnO/Ga2O3 interface because of the small energy level between the oxygen vacancy defect level and conduction band minimum (CBM) of the ZnO layer, which could easily trigger the charge transfer in the interface region. The 2DEG can be realized on the partially ordered microstructure of the Ga2O3 layer. With the assistance of the ALD technique, the thickness of the ZnO/Ga2O3 heterostructure can be as thin as ∼65 nm, which is favorable for devices of stack or ultrathin structures. Moreover, the low temperature deposition by ALD can be adopted for flexible or stretchable devices. [ABSTRACT FROM AUTHOR]

Flexible metal-oxide-semiconductor capacitors in a vertical structure using the single-crystalline Si nanomembrane (NM) with a HfO2/Al2O3 bilayer gate stack prepared by atomic layer deposition have been fabricated on plastic substrates by flip-transfer printing of Si NM/Ti/Au based trilayer heterostructures (1.3 cm × 0.9 cm × 360 nm). The electrical properties of the bilayer structure exhibit an excellent improved capacitance-voltage (C-V) frequency dispersion feature associated with an inhibited weak inversion hump and significantly larger accumulation capacitance, thus indicating the effectiveness of the passivation utilizing bilayer high-k dielectrics on a Si NM channel compared with monolayer HfO2. A comprehensive electromechanical characterization has been conducted for HfO2/Al2O3 stacked structures to investigate the effect of bending strain on C-V characteristics, leakage current density, and the associated evolution of interface charges. The presented research will be beneficial to realizing high performance thin-film transistors with lower operating voltage and higher driving current required in emerging flexible and stretchable electronics via optimized design of a nanolaminate gate stack and understanding the impact of mechanical strains on the electrical behavior of such MOS devices. [ABSTRACT FROM AUTHOR]

Magnesium-doped boron nanoswords were synthesized via a thermoreduction method. The as-prepared nanoswords are single crystalline and β-rhombohedral (β-rh) phase. Electrical transport measurements show that variable range hopping conductivity increases with temperature, and carrier mobility has a greater influence than carrier concentration. These results are consistent with the three dimensional Mott's model (M. Cutler and N. F. Mott, Phys. Rev. 181, 1336 (1969)) besides a high density of localized states at the Fermi level compared with bulk β-rh boron. Conductivity of Mg-doped boron nanoswords is significantly lower than that of 'pure' (free of magnesium) boron nanoswords. Electron energy loss spectroscopy studies confirm that the poorer conductivity arises from silicon against magnesium doping. [ABSTRACT FROM AUTHOR]