富锌条件下生长氮掺杂氧化锌薄膜的光学和电学性质

Optical and Electrical Properties of N-doped ZnO Grown in Zn-rich Condition

报道了采用等离子体辅助分子束外延方法(P-MBE),利用NO作为N源和O源,在c-面蓝宝石(c-Al2O3)衬底上外延生长了N掺杂ZnO薄膜。X射线衍射谱(XRD)和吸收谱中都出现了不同于未掺杂样品的特性,X射线光电子谱(XPS)中也发现了N的受主信号。但是在霍尔效应(Hall-effect)测量中,发现该样品并没有出现预期的p型导电特性,而是出现载流子浓度很高(2.15×1020cm-3)的n型导电特性。结合XPS结果和理论分析,认为在富Zn条件下生长会导致过量的填隙Zn原子,补偿了全部的受主后,又促使其出现了从半导体-金属的Mott转变。

N-doped zinc oxide （ZnO） thin films grown on c-face sapphire （c-Al2O3） substrate by plasmaassisted molecular beam epitaxy （P-MBE） in Zn-rich condition were reported. NO gas activated by a radio frequency source was used as both oxygen and nitrogen sources. The crystalline structure, chemical composition and electrical properties were investigated by X-ray diffraction （XRD） spectra, X-ray photoemission spectra （XPS） and temperature-dependent Hall effect measurement. In XRD spectra, the full width at half maximal （FWHM） of （0002） diffraction peak for N-doped ZnO was broader than that of undoped sample due to the incorporation of nitrogen atoms in the N-doped ZnO film. At the same time, X-ray photoelectron spectra （XPS） showed the atomic fractions for N, Zn and O are 1.1% 53.7% and 45.2%, respectively. XPS results proved nitrogen atoms had occupied the oxygen lattice and acted as acceptors. It also proved that ZnO was grown in a Zn-rich condition in the experiment. However, the Hall effect measurement （ at room temperature） showed the sample was still n-type conduction with a higher carrier concentration （2.15×10^20cm^-3）. This concentration was much higher than that of undoped sample （ 10^18 cm^-3 ）. In order to further investigate the electrical property of ZnO, the sample was annealed in 02 ambient at 500 % for 30 rain. The temperature dependent of Hall effect measurements showed different behaviors between the as-grown and the annealed samples. Before annealing, the as-grown sample showed metal conduction behavior, while it showed normal semiconductor conduction behavior after annealing. Accordmg to theory analysis and calculation, it was believed after compensating the limited acceptor （nitrogen atoms occupied the oxygen lattice）, the behavior for residual ZnO atoms is similar to heavy-doped conduction in ZnO sample and caused the ZnO sample changed from semiconductor conduction to metal condution behavior （Mott transition）.