ZnO-based optoelectronics and transparent electronics are hot topics in the field of information and materials science in recent years. Theoretically, the bandgap of ZnO-based alloys can be tuned over a wide range of wavelengths by doping with elements such as Mg and Be. For example, by adjusting the Mg composition in MgxZn1-xO, the band gap can be in the range of 3.37 to 7.8 eV. (368 ~ 159nm) within the range of regulation, which can cover the 282 ~ 220nm blind band, has become another important blind after the AlGaN UV detection materials. As a core component, the solar-blind ultraviolet detector has important application value in many fields and is a research and development focal point in the high-tech field of optoelectronics.
Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics (CPC) Du Xiaolong Research Group (E04) has continuously carried out a series of research work on the electrical regulation of dual-color/multicolor detection performance and the electrical control of sun-blind MgZnO single crystal films. Some important progress has been made. Using energy band engineering, they obtained a single wurtzite W-MgZnO single crystal film with a magnesium component of more than 50% on sapphire and silicon substrates, and epitaxially grown Zn components on a MgO(100) substrate. Up to 70% of a single rock salt RS-Zn0.7Mg0.3O single crystal thin film, the band gap of these materials are in the important band of the blind ultraviolet. Since non-doped films are semi-insulating, in order to improve their conductivity, it is not necessary to increase their background electron concentration by n-type doping. The conventional Al/Ga/In III group doping efficiency is very low, and carrier regulation cannot be realized because the energy of the Al/Ga/In donor is as the Mg component increases to 40% or more. The grade deepens quickly and cannot be ionized at room temperature.
Therefore, the n-type doping of the solar-blind MgZnO single-crystal thin film is a difficult problem that affects the application of optoelectronic devices. Mei Zengxia, Liu Lishu, Hou Yanan, Liang Huili, etc., through the self-purification of crude pure ZnF2 powder, obtained high-purity ZnF2 particles as a dopant, and successfully used rf-MBE method to achieve effective in the day-blind W-MgZnO single crystal thin film. The F-doping study shows that the oxygen-site FO is a shallow donor in the sun-blind W-MgZnO and has two energy levels of 17 meV and 74 meV, corresponding to two cellular configurations. When the F doping concentration is 1.0×10 19 cm −3 , the electron carrier concentration is 2.9×10 17 cm −3, and the conductivity is improved by 4 orders of magnitude compared with the non-doped sample. The doping technology effectively solves the problem of the conductivity of the solar-blind W-MgZnO single-crystal thin film, and the performance of related UV detectors has been greatly improved. Some results were published in the recent Scientific Reports [Sci. Rep. (2015) 5, 15516].
UV dual-color and multi-color detection has attracted wide attention because of its very important application value. The research group used the solid foundation of UV MgZnO materials and devices in the previous stage to carry out MgZnO-based bicolors [Appl. Phys. Lett. (2013) 102, [153510] and multicolor [Appl. Phys. Lett. (2014) 105, 133510] The development of prototype devices for UV detectors has achieved significant progress. By designing a multi-layer MgxZn1-xO film structure with different Mg components and using an asymmetric potential well formed by the energy band offset between the Si substrate and the MgZnO epitaxial layer, a novel UV-controllable two-color detector was constructed. In the technical solution, by changing the polarity of the working bias, it is possible to obtain different ultraviolet signals in the blind spot or the blind zone, thereby realizing the production of a Si-based monolithic integrated dual-color ultraviolet detector prototype device. In order to achieve the single-chip multi-band UV detection function, they epitaxially grown a Mg composition gradient MgZnO epitaxial thin film on a ZnO substrate, in order to filter out the photoresponse of the ZnO substrate, before the deposition of MgZnO epitaxial BeO buffer layer, using it The large dielectric constant and denseness have successfully blocked the upstream transport of ZnO photocurrent. Combined with a bandgap-graded W-MgZnO film, the detection band can be conveniently selected using the bias voltage to realize the multi-color ultraviolet band. Detection function. The reviewers of APL highly praised this new-principle polychromatic detector, and believe that this method can be a paradigm for future device design.
The above work was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China and the Chinese Academy of Sciences. The device development work was completed in cooperation with the Gu Changzhi Research Group of the Micromachining Laboratory. The results of the SIMS and variable temperature Hall tests were obtained from the Andrej Kuznetsov group at the University of Oslo, Norway.
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