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ZnO薄膜中的高的背景电子浓度能够对p型掺杂形成补偿,从而对p型掺杂造成障碍,了解高背景电子浓度的来源有助于对p型掺杂的研究。本文采用分子束外延技术在不同真空度下在a面蓝宝石衬底上生长了一系列氧化锌薄膜,发现在低真空度下生长的样品的载流子浓度较高,为1019cm-3量级;而高真空度下生长的样品,其载流子浓度比低真空生长的样品显著降低,降低了3个数量级。在相同条件下生长的样品,通过不同的后处理手段进行处理后,其电子浓度未发生明显变化,说明氧空位等本征缺陷不是ZnO薄膜中电子的主要来源,高背景电子浓度应该与生长过程中非故意引入的杂质相关。通过低温光致发光表征,发现低真空度下生长的样品在低温下3.366 eV处有强的施主束缚激子发光峰,而高真空度下生长的样品的此发光峰显著变弱。由此,高电子浓度被归结为与生长过程中非故意引入的氢杂质相关。
The high background electron concentration in ZnO films can compensate for p-type doping, which hinders p-type doping. Understanding the source of high background electron concentration is helpful for the study of p-type doping. In this paper, a series of ZnO thin films were grown on a-plane sapphire substrate by molecular beam epitaxy at different vacuum levels. The results showed that the carrier concentration of samples grown under low vacuum was higher than 1019 cm-3. However, the sample grown under high vacuum had a significantly lower carrier concentration than the sample grown under low vacuum, which was reduced by 3 orders of magnitude. The samples grown under the same conditions were treated by different post-treatment methods without any significant change in their electron concentration, indicating that intrinsic defects such as oxygen vacancies are not the main source of electrons in the ZnO thin film. The high background electron concentration should be related to the growth process The impurity introduced by China-Africa is relevant. By low temperature photoluminescence characterization, it was found that the sample grown under low vacuum had a strong donor-bound exciton emission peak at 3.366 eV at low temperature, while the emission peak of the sample grown under high vacuum was significantly weaker. Thus, the high electron concentration is attributed to hydrogen impurities that are not deliberately introduced during growth.