| ZnO is representative of ?-? semiconductors, with new research indicating that technology based on the material may be highly significant in the future of device application areas. Based on the fabrication of p-n junctions; great efforts have been devoted to fabricate light-emitting diodes, laser diodes, photodetectors and transistors. In recent years, the application of ZnO devices has been extended to solar cell materials and flexible substrate materials, these applications require ZnO-based devices must be further reduced thickness, both to improve the transmittance, while reducing the crystal stress. Therefore, reducing the thickness, while improving the luminous gain of ZnO-based devices, enhance the electron density and increase the transmission rate is the urgent problem to be solved. From the present study, it is known that the insertion of a suitable quantum barrier in a ZnO-based device is a solution. Thus selection, structural design of the barrier material becomes the key to solving the problem.In this paper, in order to research the luminescence properties and photoelectron transport mechanism of ZnO p-n homojunction devices, a ZnMgO quantum barrier technique is embeded inp-ZnO:(Li, N)/ n-ZnO junction device. It is found that the carrier concentration and mobility are obviously improved by using this technique.We first prepared a film series D series of samples x and thickness ratio of ZnO/ Zn1-xMgxO. The microstructures, optical properties and electrical transport properties of the films were analyzed, which were provieded the basic data for constructing the quantum barriers. Then we design and fabricate the Zn1-xMgxO asymmetric double barriers (ADB) named E series. The quantum confinement effect of ZnMgO multi-quantum barrier appeared at room temperature. We have prepared two different groups of ZnO homo p-n junctions, one of which are Q-series with ADB structure embedded and the other H-series without it. The influence of the embedded ADB is summarized.Through the systematic analysis of the above experiments, the following innovations are obtained:1. The ZnO/Znl-xMgxO layered thin films (D series) and the E series thin films with asymmetric multi-quantum barrier (ADB) structure were prepared by laser deposition technique. The two series of samples are all along the c-Axis oriented hexagonal wurtzite structure. And the use of Li-N composite doping technology overcome difficult to prepare p-type conductive ZnO semiconductor for ZnO p-n homojunction structure for Si-based device applications. At the same time, ZnO/ ADB/Zn1-xMgxO thin films (Q series) have been fabricated successfully by using a new ADB structure, which lays a foundation for the realization of quantum barrier devices. In some key technology has made innovative research results.2. The electrical and optical properties of D series were analyzed. It was found that there existed 2-dimensional electron gas (2DEGs) with high mobility in the interface of ZnO/Zn1-xMgxO thin films. The 2DEGs mobility is affected by the film thickness of Zni-xMgx0 and the value of x. Zn1-xMgxO film with larger film thickness and smaller x value, can have higher carrier mobility. Therefore, the x should be small than 0.35 in order to construct an appropriate Zn1-xMgxO ADB structure. The band gap of Zn1-xMgxO thin films is higher than ZnO thin films. This provides the basis for constructing Zn1-xMgxO multiple quantum barrier in ZnO.3. The E series were systematically studied. In the absorption spectrum, we have successfully observed the step shape of the two-dimensional density of electrons in E series, which clearly shows that the ZnMgO ADB structure has realized the quantum-binding effect at room temperature. In the photoluminescence (PL) spectrum, the emission peak in the visible region disappears and the main emission peak of the ZnO exciton increases, indicating that the ZnO potential well in the ZnMgO barrier layer is the active layer, and the ADB structure enhances the exciton Luminous effect. The analysis of the electrical properties shows that E series has a high carrier concentration, but the carrier mobility decreases due to the enhancement of the quantum scattering effect.4. At room temperature, absorption spectra of the Q-series ZnO pn homojunctions which represent typical step effects of the two-dimensional density states, appear again. It further confirms that the quantum-binding effect of ZnMgO ADB appears at the p-n junction interface, along the ZnO<002> axis direction. In comparison with the photoluminescence spectra of H-series, it has been found that the Q-series quantum barrier significantly limits the transition in the visible region. This also confirms that the Quantum-binding effect is the main reason for the optical gain.Compared with the H series, ADB in Q-series p-n junction reduce the minimum thickness about 44%. The Field-induced inter-band tunnelling effect appears when Q is under the reverse voltage, and the embedded ZnMgO multi-quantum barrier overcomes the problem of the decrease of mobility and the increase of resistivity which due to the quantum scattering effect, then the 2DEGs mobility increase again.The device modification demonstrates increased performance in both rectifying characteristics and PL properties.The Embedded ZnMgO ADB in Q device improve the performance of ZnO p-n homojunctions. It is meaningful for the application of ZnO based junction devices. |
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