Ultraviolet (UV) photodetection has drawn a great deal of attention in recent years due to a wide range of civil and military applications. Because of its wide band gap, low cost, strong radiation hardness and high chemical stability, ZnO are regarded as one of the most promising candidates for UV photodetectors. Additionally, doping in ZnO with Mg elements can adjust the bandgap largely and make it feasible to prepare UV photodetectors with different cut-off wavelengths. ZnO-based photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes and p–n junction photodetectors have been developed. In this work, it mainly focuses on the ZnO and ZnMgO films photodetectors. We analyze the performance of ZnO-based photodetectors, discussing recent achievements, and comparing the characteristics of the various photodetector structures developed to date.

https://www.mdpi.com/1424-8220/10/9/8604/pdf

ZnO-Based Ultraviolet Photodetectors

Laser molecular beam epitaxy technology has been employed to deposit β-gallium oxide (β-Ga2O3) on (0001) sapphire substrates. After optimizing the growth parameters, (2¯01)-oriented β-Ga2O3 thin film was obtained. Ultraviolet-visible absorption spectrum demonstrates that the prepared β-Ga2O3 thin film shows excellent solar-blind ultraviolet (UV) characteristic with a band gap of 5.02 eV. A prototype photodetector device with a metal-semiconductor-metal structure has been fabricated using high quality β-Ga2O3 film. The device exhibits obvious photoresponse under 254 nm UV light irradiation, suggesting a potential application in solar-blind photodetectors.

Fabrication of β-Ga_2O_3 thin films and solar-blind photodetectors by laser MBE technology

Ultrafast-response (20 μs) UV detectors, which are visible-blind and self-powered, in devices where an n-type ZnO nanowire partially lies on a p-type GaN film, are demonstrated. Moreover, a CdSe-nanowire red-light detector powered by a nanoscale ZnO/GaN photovoltaic cell is also demonstrated, which extends the device function to a selective multiwavelength photodetector and shows the function of an optical logical AND gate.

Self-powered, ultrafast, visible-blind UV detection and optical logical operation based on ZnO/GaN nanoscale p-n junctions.

Because of the direct band gap of 4.9 eV, β-Ga2O3 has been considered as an ideal material for solar-blind photodetection without any bandgap tuning. Practical applications of the photodetectors require fast response speed, high signal-to-noise ratio, low energy consumption and low fabrication cost. Unfortunately, most reported β-Ga2O3-based photodetectors usually possess a relatively long response time. In addition, the β-Ga2O3 photodetectors based on bulk, the individual 1D nanostructure, and the film often suffer from the high cost, the low repeatability, and the relatively large dark current, respectively. In this paper, a Au/β-Ga2O3 nanowires array film vertical Schottky photodiode is successfully fabricated by a simple thermal partial oxidation process. The device exhibits a very low dark current of 10 pA at −30 V with a sharp cutoff at 270 nm. More interestingly, the 90–10% decay time of our device is only around 64 μs, which is much quicker than any other previously reported β-Ga2O3-based photodet...

Self-Powered Solar-Blind Photodetector with Fast Response Based on Au/β-Ga2O3 Nanowires Array Film Schottky Junction

A high sensitivity self-powered solar-blind photodetector is successfully constructed based on the polyaniline/MgZnO bilayer. The maximum responsivity of the photodetector is 160 μA W-1 at 250 nm under 0 V bias. The device also exhibits a high on/off ratio of ≈104 under 250 nm illumination at a relatively weak light intensity of 130 μW cm-2 without any power.

Ultrasensitive Self-Powered Solar-Blind Deep-Ultraviolet Photodetector Based on All-Solid-State Polyaniline/MgZnO Bilayer.

ZnO is a wide-bandgap (3.37 eV at room temperature) oxide semiconductor that is attractive for its great potential in short-wavelength optoelectronic devices, in which high quality films and heterostructures are essential for high performance. In this study, controlled growth of ZnO-based thin films and heterostructures by molecular beam epitaxy (MBE) is demonstrated on different substrates with emphasis on interface engineering. It is revealed that ultrathin AlN or MgO interfacial layers play a key role in establishing structural and chemical compatibility between ZnO and substrates. Furthermore, a quasi-homo buffer is introduced prior to growth of a wurtzite MgZnO epilayer to suppress the phase segregation of rock-salt MgO, achieving wide-range bandgap tuning from 3.3 to 4.55 eV. Finally, a visible-blind UV detector exploiting a double heterojunction of n-ZnO/insuIator-MgO/p-Si and a solar-blind UV detector using MgZnO as an active layer are fabricated by using the growth techniques discussed here.

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Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

http://oxidesemi.iphy.ac.cn/EN/paper/2009/2009-JCG-311(18)-4356-Liu%20ZL.pdf

Solar-blind 4.55 eV band gap Mg0.55Zn0.45O components fabricated using quasi-homo buffers

Synthesis and characterization of well-aligned Zn1-xMgxO nanorods and film by metal organic chemical vapor deposition

We report the 87Sr optical lattice clock developed at the National Time Service Center. We achieved a closed-loop operation of the optical lattice clock based on 87Sr atoms. The linewidth of the spin-polarized clock peak is 3.9 Hz with a clock laser pulse length of 300 ms, which corresponds to a Fourier-limited linewidth of 3 Hz. The fitting of the in-loop error signal data shows that the instability is approximately , affected primarily by the white noise. The fractional frequency difference averages down to for an averaging time of 3000 s.

https://iopscience.iop.org/article/10.1088/1674-1056/27/2/023701/pdf

Strontium optical lattice clock at the National Time Service Center

A single crystalline Mg2Si film was formed by solid phase reaction (SPR) of a Si(111) substrate with an Mg overlayer capped with an oxide layer(s), which was enhanced by post annealing from room temperature to 100 degrees C in a molecular beam epitaxy (MBE) system. The thermal stability of the Mg2Si film was then systematically investigated by post annealing in an oxygen-radical ambient at 300 degrees C, 450 degrees C and 650 degrees C, respectively. The Mg2Si film stayed stable until the annealing temperature reached 450 degrees C then it transformed into amorphous MgOx attributed to the decomposition of Mg2Si and the oxidization of dissociated Mg.

https://iopscience.iop.org/article/10.1088/1674-1056/18/7/078/pdf

Yang Guo

Papers

Controlled Growth of High-Quality ZnO-Based Films and Fabrication of Visible-Blind and Solar-Blind Ultra-Violet Detectors

Solar-blind 4.55 eV band gap Mg0.55Zn0.45O components fabricated using quasi-homo buffers

Synthesis and characterization of well-aligned Zn1-xMgxO nanorods and film by metal organic chemical vapor deposition

Strontium optical lattice clock at the National Time Service Center

Thermal stability of Mg2Si epitaxial film formed on Si (111) substrate by solid phase reaction