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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]

Recently, localized surface plasmon resonance of noble metal nanoparticles has been widely used to broaden the photoresponse of wide-band-gap semiconductors. In this work, Au nanoparticles with different sputtering time were prepared via ion sputtering and thermal treatment on ZnO thin films prepared by magnetron sputtering. The influence of the Au nanoparticle sputtering time on the absorbance of the Au/ZnO nanocomposite was investigated. The results show that Au/ZnO nanocomposites have enhanced UV absorption and broad absorption bands around 580–600 nm compared with ZnO without Au nanoparticles, which are attributed to the band-to-band excitation of ZnO and localized surface plasmon resonance of gold nanoparticles. Under the illumination of UV light, electrons are excited from the valence band to conduction band of ZnO, while hot electrons are transferred from Au nanoparticles with smaller particle size to ZnO, resulting in the generation of photocurrent. Under the illumination of visible light, only hot electrons are transferred from Au nanoparticles with larger particle size to ZnO, leading to the generation of photocurrent. Then the influence of sputtering time on the dark current and IXenon lamp/IDark of the photodetectors was investigated. The results show that Au nanoparticles are able to decrease the dark current of photodetectors and influence the photoresponse under visible light illumination. [ABSTRACT FROM AUTHOR]

A series of cubic MgZnO films with a band gap of 5.0 eV (240 nm) are grown on the Si substrate by radio-frequency (rf) magnetron sputtering with various annealing temperature. Highly (111) textured single phase cubic MgZnO films with enhancement of conductivities are received through thermal annealing. The effects of annealing temperature on the structural, optical and electrical properties of cubic MgZnO films have been investigated. With increasing annealing temperature, phase separation of MgZnO films has been suppressed due to the internal strain is partially relieved by the thermal annealing. In addition, the resistivity (electron mobility, carrier concentration) decrease (increase) with an increase of annealing temperature which implies that high temperature annealing could improve the crystal quality and thereby reduce the grain boundary scattering for electron transport. Our results represent a meaningful step toward fabrication of high quality cubic MgZnO thin films use in UVC region. [ABSTRACT FROM AUTHOR]

In this work, (Al x Ga 1-x) 2 O 3 thin films were grown on Al 2 O 3 (0001) substrate by radio frequency magnetron sputtering using Al/Ga 2 O 3 target. The analysis of crystalline structure, morphology, transmittance and bandgap after various annealing temperatures were investigated in detail. The films were oriented along ( 2 — 01) plane, and the crystalline quality improved with increasing annealing temperature. The stoichiometries of films can be regard as (Al 0.33 Ga 0.67) 2 O 3 according to X-ray photoelectron spectroscopy and the additional compressive stress in the sample which annealed at 900 °C was certified. The bandgap of annealed films was totally decreased due to increasing magnitude of compressive stress and grain size. Therefore, these results may suggest the way to tune the band gap of β-(Al x Ga 1-x) 2 O 3 films by varying the residual stress through annealing and indicate the optimum annealing temperature for (Al 0.33 Ga 0.67) 2 O 3 thin films is about 800 °C. • The (Al x Ga 1-x) 2 O 3 films were deposited using Al/Ga 2 O 3 target. • All the samples were monoclinic structure with the (−201) preferred orientation. • Post-annealing can improve the crystalline of (Al x Ga 1-x) 2 O 3 thin films. • The remigration of Al atoms took place after annealing at 900 °C. [ABSTRACT FROM AUTHOR]

In this work, Ga 2 O 3 thin films were grown on Al 2 O 3 (0001) substrate by radio frequency magnetron sputtering. The influence of sputtering power on crystalline structure, morphology, transmittance, band gap, and photoluminescence were investigated in detail. X-ray diffraction results showed that the β-Ga 2 O 3 films were oriented along ( 2 ¯ 01 ) plane, and the crystalline quality improved with increasing sputtering power. Scanning electron microscope images revealed that the proportion of large-size grain increased with increasing sputtering power. The β-Ga 2 O 3 films displayed very high transmittance close to 100% in visible region. Photoluminescence spectra showed that all the films exhibited intense blue and green emission centered at approximately 430 nm and 550 nm originated from the donor-acceptor pair recombination. [ABSTRACT FROM AUTHOR]

• The blue and green emission in β-Ga 2 O 3 were modulated by intrinsic defects. • Green emission in β-Ga 2 O 3 film originated from isolated gallium vacancies. • Isolated oxygen vacancies can't play the role in blue emission independently. • Blue emission resulted from complex oxygen-defects. In this work, the β-Ga 2 O 3 films were fabricated by radio frequency magnetron sputtering on the c-plane sapphire substrates with the (2 ¯ 01) preferred orientation. The blue and green luminescence of β-Ga 2 O 3 films have been systemically studied. By changing the concentration of intrinsic vacancies in β-Ga 2 O 3 films through increasing oxygen flow rate during sputtering, the intensity of blue and green luminescence were modulated. The maximum value of the intensity ratio for green luminescence to blue luminescence reached to 433.37% when the oxygen flow rate arrived at 6 sccm. Combining experiments with density functional theory calculations, this work had proved the green luminescence in β-Ga 2 O 3 mainly originated from the isolated gallium vacancies. While the isolated oxygen vacancies could not play the important roles in the blue emission independently. The blue luminescence most likely resulted from complex defects such as (V O I + V Ga I ) − or the optical transitions between V O and (V O , V Ga). Thus, changing the concentration of intrinsic vacancies is highly effective for β-Ga 2 O 3 to modulate the intensity of green luminescence and blue luminescence. [ABSTRACT FROM AUTHOR]

The (In x Ga 1-x) 2 O 3 thin films were deposited on sapphire substrates by radio frequency magnetron sputtering with increasing sputtering pressure from 0.6 Pa to 1.6 Pa. X-ray diffraction analysis indicated In composition of (In x Ga 1-x) 2 O 3 thin films maintained constant with the increase of sputtering pressure and In content and bandgaps of (In x Ga 1-x) 2 O 3 thin films were estimated to be 6% and 4.78 eV by Vegard's law, respectively. The influence of sputtering pressure on structural and optical properties was discussed in detail. Especially, the origin of different emission of (In x Ga 1-x) 2 O 3 thin films was investigated. The role of V Ga defects on the green emission centered at about 550 nm had been clarified. The energy band diagram of (In x Ga 1-x) 2 O 3 thin film was also proposed with intrinsic defect levels. • In content of (In x Ga 1-x) 2 O 3 films is 6% for all sputtering pressure condition. • Defects play an important role in luminescence. • Green luminescence is related to gallium vacancies. [ABSTRACT FROM AUTHOR]