| ZnO is a direct band gap semiconductor, which has band gap of 3.37eV at room temperature, and the binding energy of exciton as high as 60meV. Owing to so many advantages, ZnO has been considered as the ideal semiconductor material to manufacture the short-wavelength optoelectronic devices (such as UV light-emitting diodes, laser), and preparation of high-performance p-type ZnO has become the key problem of its application. According to the present research, the difficulties of preparation of p-type ZnO mainly come from the following two reasons: first, intrinsic defects (such as oxygen vacancies (Vo), interstitial zinc (Zni) or impurities H) caused self-compensation effect; second, the solid solution of doped elements in ZnO is low and has a deep acceptor level. For the first problem, by improving the crystal quality to reduce self-compensation effect; For the second problem, because pressure can change the thermodynamic equilibrium state of system, so it is considered as an effective mean in raising the solid solution of accepter .Based on the above considerations, we applied high pressure and temperature (HPHT) technology in preparation of p-type ZnO and hope to enhance the acceptor doping concentration to obtain p-type ZnO with stability, low resistivity, high carrier concentration. However, test results show that the p-type electrical properties of sample is not from the doping, but from the interface state which is formed in grain boundaryIn addition, to meet the requirements of ZnO-based light-emitting devices, we also applied HPHT technology in preparation of intrinsic n type ZnO, as a result, produced the transparent ZnO ceramic materials with better electrical and optical properties at certain pressure and temperature conditions.The details and conclusions are as follows:1,The transparent ZnO ceramics with the structure of wurtzite has been prepared at 5.0GPa and 800℃for the first time, breaking the restriction that the oxide with the hexagonal structure is difficult to be prepared to the transparent ceramics without the additive. Moreover, the ZnO transparent ceramics prepared by the high pressure technology has the excellent electrical and optical properties. Its carrier concentration was 8.36×1018cm-3, the resistivity was 0.57?.cm and the mobile was 23cm2V-1s-1. The stronger free exciton emission was presented at 3.37eV.2,P-type ZnO has been prepared by the high pressure technology with the pressure of 5.0GPa, temperature range from 800-1450℃and the atomic ratio(Sb atomic/total atomic) of initial sample vary from 1.4% to 8.7% . The sample with better properties was prepared at the conditions of 5.0GPa and 1450℃, its resistivity was 1.254×10-1(Ωcm), carrier concentration was 1.023×1019(cm-3) and the mobile was 4.852(cm2V-1s-1).3,P-type conduction mechanism of ZnO/Sb sample was discussed. The changes of SEM and EDX of sample before and after annealing and the results of XRD and XPS showed that Sb element exists in two forms, one exists in the grain boundary as metal Sb; the other exists in the (Zn, Sb, O) ternary compounds and the p-type conductivity of the samples comes from band bending formed by elemental Sb in grain boundaries.4,The decomposition phenomenon of Sb2O3 was found accidentally at high pressure condition, a series of experiments were carried out to discuss the relationship between decomposition behavior and pressure (temperature), and gave the relevant thermodynamic mechanism... |
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