Effect of high temperature annealing on defects and optical properties of ZnO single crystals

Abstract

Hydrothermal grown ZnO single crystals were annealed in N2 or O2 between 900 and 1300 °C. Positron lifetime measurements reveal a single lifetime in all the ZnO samples before and after annealing. The positron lifetime is about 181 ps after annealing at 900 °C in either N2 or O2 atmosphere. However, increase of the positron lifetime is observed after further annealing the sample at higher temperatures up to 1300 °C, and it has a faster increase in O2 ambient. Temperature dependence measurements show that the positron lifetime has very slight increase with temperature for the 900 °C annealed sample, while it shows notable variation for the sample annealed at 1300 °C. This implied that annealing at high temperature introduces additional defects. These defects are supposed to be Zn vacancy‐related defects. Cathodoluminescence (CL) measurements indicates enhancement of both UV and green emission after annealing, and the enhancement of green emission is much stronger for the samples annealed in O2 ambient. The possible origin of green emission is tentatively discussed.

Effect of microwave irradiation on the electronic structure of ZnO

“…3.36 eV room temperature, respectively. The band at 2.20 eV in Fig.3 reportedly originates from 1 the defect level [22,24,26]. In addition, the broad PL emission band, which is observed 2 for all excitation energies (2.92-3.42 eV) is similar to the case for a large Stokes-shift 3 PL.…”

“…The broad 16 peak shifts from 2.31 eV to 2.20 eV as the excitation energy is elevated from 3.23 eV to 173.35 eV (Phenomenon 4). 18The peak at 2.20-2.40 eV in ZnO is attributed to point defects such as oxygen 19 vacancies, zinc vacancies, zinc interstitials, oxygen interstitials, and oxygen-antisites 20[21][22][23][24][25][26][27]. The electron transition process changes as the excitation energy is swept and 21 has a maximum of approximately 2.31 eV when the excitation energy is 3.23 eV.…”

Zinc Oxide Grown by Atomic Layer Deposition: From Heavily n‐Type to p‐Type Material

“…[71,72] and references therein). The lower n , at the level of 10 14 cm −3 , is only reported for single zinc oxide crystals grown by the hydrothermal method where group I elements are incorporated as unintentional dopants, likely contributing to a self‐compensation effect …”

“…Among these are sensors, surface acoustic wave devices, transparent electrodes for solar cells, transparent electronics, ultraviolet light emitters, and others. An additional advantage of this material, important for applications, is feasibility to grow a wide range of nanostructures, thin films, and single crystals . The latter ones provide good quality single‐crystal substrates for a homoepitaxy .…”

Towards understanding the hydrogen molecule in ZnO

“…It was also shown, that subsequent annealing results in a significant decrease of lattice strain [71]. Recently, zinc vacancy-related defects were shown to be formed after annealing ZnO in oxygen or nitrogen atmosphere above 900 • C [72].…”