Self-powered photodetectors can work with low power consumption or even without any supply from external power sources, and they are recognized as one of the developing trends of next-generation optoelectronic devices. As one of the most-known n-type metal oxides applied in electronic devices, ZnO nanostructures and their heterostructures with other appropriate materials have been widely applied in the assembly of self-powered UV photodetectors. In this review, the recent research on different types of ZnO-based self-powered UV photodetectors is outlined. ZnO nanostructures with different dimensionalities adopted in these photodetectors are discussed in detail. The influences of specific effects, such as the piezo-phototronic effect, the pyro-phototronic effect, the photo-gating effect, and even their fusions, on modulating the self-powered photo-response of these photodetectors have also been demonstrated. The applications of these photodetectors in UV sensing, environmental recognition, wearable devices, functional devices, and light communication are displayed. Finally, possible opportunities and directions for the future developments of these photodetectors are proposed.

Self-powered UV photodetectors based on ZnO nanomaterials

Broadband Ultraviolet Photodetector Based on Vertical Ga2O3/GaN Nanowire Array with High Responsivity

https://iopscience.iop.org/article/10.1088/1674-1056/28/4/048503/pdf

Ultraviolet photodetectors based on wide bandgap oxide semiconductor films

The integration of lead sulfide quantum dots (QDs) with a high-conductivity material that is compatible with a scalable fabrication is an important route for the applications of QD-based photodetectors. Herein, we first developed a broadband photodetector by combining amorphous ZnO and PbS QDs, forming a heterojunction structure. The photodetector showed detectivity up to 7.9 × 1012 and 4.1 × 1011 jones under 640 and 1310 nm illumination, respectively. The role of the oxygen background pressure in the electronic structure of ZnO films grown by pulsed laser deposition was systematically studied, and it was found to play an important role in the conductivity associated with the variation of the oxygen vacancy concentration. By increasing the oxygen vacancy concentration, the electron mobility of amorphous ZnO layers dramatically increased and the work function decreased, which were beneficial for the photocurrent enhancement of ZnO/PbS QD photodetectors. Our results provide a simple and highly scalable approach to develop broadband photodetectors with high performance.

Amorphous ZnO/PbS Quantum Dots Heterojunction for Efficient Responsivity Broadband Photodetectors

A novel self-powered solar-blind ZnGa2O4 ultraviolet (UV) photodetector has been constructed by fabricating asymmetric pairs of Au Schottky electrodes on the ZnGa2O4 film. The current-voltage curve of the device exhibits an obvious rectifying characteristic with a rectification ratio of 11.3 at ±8 V. At 0 V bias, the peak responsivity of our device at 246 nm is about 22.2 mA/W with an UV–vis rejection ratio of 1.3× 10 4 , indicating the excellent self-powered solar-blind UV photodetector performance. More interestingly, the rise time and decay time of the device are only 10 ns and 30 ns, respectively, which are much faster than that of any other previously reported self-powered solar-blind UV photodetectors to the best of our knowledge. The ultra-fast response speed of the device should be attributed to the asymmetric Schottky junctions and the high crystalline quality of our ZnGa2O4 film with low trap density. Our work provides a new method to constructing high-performance self-powered solar-blind UV photodetectors.

Self-powered solar-blind ZnGa2O4 UV photodetector with ultra-fast response speed

A high performance p-GaN/n-ZnMgO heterojunction photodiode was demonstrated and investigated. A high quality p-GaN film was grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy and subsequently an n-ZnMgO layer was deposited on p-GaN by a metal organic chemical vapor deposition technique. The p-GaN/n-ZnMgO heterojunction photodetector shows a clear rectifying I–V characteristic with a turn-on voltage of 2.5 V. At zero-bias voltage, the device shows a high peak responsivity of 196 mA W−1 at 362 nm. The 10–90% rise time and 90–10% decay time of the device can be as short as 1.7 ms and 3.3 ms, respectively. The excellent crystal quality and electrical properties of p-GaN play an important role in the high performance of the photodiode. This work provides a feasible way for the development of high-performance heterojunction self-powered UV detectors.

A high performance self-powered ultraviolet photodetector based on a p-GaN/n-ZnMgO heterojunction

Herein, ZnMgO thin film ultraviolet (UV) photodetectors based on metal-semiconductor-metal structure were fabricated on a-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The effect of H2O2 solution treatment on the properties of the ZnMgO thin film and its UV photodetectors was investigated. After immersing the ZnMgO UV photodetector in a H2O2 solution at 100 degrees C for 3 min, the dark current of the device was reduced by more than one order of magnitude under 1 V bias, whereas the responsivity was slightly decreased. More interestingly, the response speed became much quicker and insensitive to the atmosphere after the treatment of the photodetector with H2O2 solution, which can be attributed to the reduction in the oxygen vacancy defects. Our findings may provide a promising approach for improving the performance of photodetectors.

Performance improvement of a ZnMgO ultraviolet detector by chemical treatment with hydrogen peroxide

We have demonstrated a self-powered solar-blind ultraviolet (UV) photodetector based on the Au/ZnMgO/ZnO:Al vertical structure. The comb-shaped Au was selected as the Schottky electrode due to its high transmittance (more than 60%) in the wavelength region from 200 nm to 300 nm. At 0 V bias, the detector showed a responsivity of 55 mA/W under 265 nm light illumination with the intensity of 80 nW/cm2, which is larger than that of any other previously reported ZnO-based self-powered UV photodetectors. And a fast response speed can be also clearly observed with 10%–90% rise and 90%-10% decay times of 20 μs and 300 μs, respectively. The excellent self-powered solar-blind UV detection of our Au/ZnMgO/ZnO:Al device should be associated with the high external quantum efficiency, especially for the weak signal detection. Our findings offered new chances in high-performance self-powered photodetectors fabrication.

Self-powered solar-blind ultraviolet photodetector based on Au/ZnMgO/ZnO:Al with comb-shaped Schottky electrode

Epitaxial MgGa2O4 thin films with a bandgap of 5.18 eV were grown on the c-plane sapphire substrate by using metal organic chemical vapor deposition. The structure, optical, electronic, and optoelectronic properties of MgGa2O4 thin films have been investigated before and after high-temperature annealing in an oxygen or nitrogen atmosphere. In particular, the O2-annealed MgGa2O4 thin film reveals a high crystalline quality and a low concentration of oxygen vacancies. Moreover, a quick response speed (tr = 20 ns, td = 400 ns), a low dark current (∼17 pA at 10 V), and a high UV/Visible rejection ratio (>105) can be demonstrated in the O2-annealed MgGa2O4 photodetector, indicating the excellent solar-blind ultraviolet (SBUV) photodetection characteristics. The effect of annealing atmosphere on the photoelectric properties of the film and its physical mechanism were studied. This research provides an effective way to realize high-performance SBUV photodetectors and opens up the application of MgGa2O4 spinel in the field of semiconductor optoelectronic and microelectronic devices. 

Yongxue Zhu

Papers

A high performance self-powered ultraviolet photodetector based on a p-GaN/n-ZnMgO heterojunction

Performance improvement of a ZnMgO ultraviolet detector by chemical treatment with hydrogen peroxide

Self-powered solar-blind ultraviolet photodetector based on Au/ZnMgO/ZnO:Al with comb-shaped Schottky electrode

MOCVD growth of MgGa2O4 thin films for high-performance solar-blind UV photodetectors

High-performance fully transparent Ga2O3 solar-blind UV photodetector with the embedded indium–tin–oxide electrodes