| Popis: |
Thermal effect is one of the most important factors limiting the photoluminescence performances of semiconductor devices. With the increase of temperature, the PL intensity decreases gradually due to the effect of thermal quenching. However, the abnormal negative thermal quenching effect has been found in many semiconductor materials in recent years, e.g. ZnO, BiFeO3, InPBi, etc. This effect is generally considered as the sign of the existence for middle/local energy state in the electron-hole recombination process, which usually needs to be confirmed by the temperature-dependent PL spectra. Here, we report the thermal regulation mechanism of photoluminescence in intrinsic acceptor-rich ZnO (A-ZnO) microtubes grown by the optical vapour supersaturated precipitation method. The grown A-ZnO microtube with a length of 5 mm and diameter of 100 μm has regular hexagonal cross-section morphology. Its optical band gap at room temperature is about 3.30 eV. With the increase of temperature, the PL intensity of A-ZnO microtube exhibits an abnormal behavior from the thermal quenching to the negative thermal quenching and then to the thermal quenching. The thermal quenching effect at 80–200 K is associated with regurgitation/ionization of shallow donor, thermal ionization of free exciton, and conversion of neutral acceptor bound exciton. The negative thermal quenching effect at 200–240 K is associated with thermal excitation of electrons in a deep level trap of 488 meV below the conduction band minimum (CBM). The thermal quenching effect at 240–470 K is related to Shockley-Read-Hall recombination based on the non-radiative recombination center of 628 meV below the CBM. The non-radiative recombination center and trap level are far from the acceptor level of A-ZnO microtube, which may be related to the deep-level defect of oxygen vacancy in the intrinsic A-ZnO microtube. This work establishes the temperature-dependent transition model of photo-generated carriers and reveals the thermal regulation mechanism of PL for the A-ZnO microtubes. It provides a novel platform for designing the high-temperature and high-efficiency ZnO-based photoelectric devices. |
