退火对ZnO薄膜质量的影响

Effects of Anneal on Properties of ZnO Thin Films

用金属有机化学气相沉积法(MOCVD)在蓝宝石(0001)衬底上制备了c轴取向的高质量的ZnO薄膜,通过在生长温度下氧气和氮气中退火处理的比较,研究了退火对ZnO薄膜结构和发光特性的影响。通过X射线衍射测量得知,经过氮气和氧气退火都可以使其002峰增强,且在氧退火中表现得尤为明显。光致发光测量发现氮气中退火的ZnO薄膜的紫外发光峰明显增强,而深能级发光峰明显减弱;而氧气中退火的ZnO薄膜的紫外发光峰略有减弱,而深能级峰显著增强。

ZnO is a direct and wide-band gap semiconductor with WZ crystal structure. It has recently attracted considerable attention due to its favorable properties such as the wider band gap （3.37 eV） at room temperature, the large binding energy of excitons （60 meV ） at room temperature, and highly c-axis oriented. ZnO has so good photoelectric and piezoelectric properties that it has immensity space for developing at surface acoustic wave devices, light emitting diodes （ LEDs）, photodetectors, gas sensor and solar cells etc. A variety of deposition techniques have been employed to prepare ZnO thin films, such as pulsed laser deposition （PLD） , molecule beam epitaxy （MBE） and metal-organic chemical vapor deposition （MOCVD）. Among them, MOCVD provides the advantages of large-area deposition and high throughput due to higher growth rates. Consequently, MOCVD was adopted to grow ZnO thin films. High-quality ZnO thin films were grown on sapphire （0001） substrates at 590℃ for 20 min by metal-organic chemical vapor deposition （MOCVD）. The effect of annealing under different condition on crystal structure and optical properties of ZnO thin films have been studied. The results show that the crystal quality of the films grown on c-plane has been improved largely. Especially the film annealed in oxygen, the XRD peak of ZnO （002） became stronger greatly and the FWHM of XRD peak is only 0. 11°. The PL spectra show that the deep energy level emitting disappears in the sample annealed in nitrogen. On the contrary, the deep energy level emitting became stronger for the sample annealed in oxygen. The results show that the deep energy level emitting intensity is related to the concentration of VZn and OZn defects. Additionally, the resistivity of ZnO thin films annealed in oxygen could increase remarkably for the change of the rate of Zn and O. It was an effective method to achieve the high-quality ZnO films, high-resistance ZnO films, even p-type ZnO by annealing under proper condition from our results.