Li掺杂ZnO薄膜的导电和发光特性

Electrical and Optical Characteristics of Li-doped ZnO

通过将含有原子数分数为2%锂的Zn-Li合金薄膜和金属锌薄膜在500℃氮气氛中退火2h,然后在700℃氧气氛下退火1h的方法分别制备出ZnO∶Li和ZnO薄膜。Hall效应测量表明,其导电类型分别为p型和n型。通过He-Cd激光器的325nm线激发,测量了样品室温和低温(12K)光致发光光谱,并根据ZnO∶Li薄膜的低温发光光谱特征,计算出Li相关受主能级位于价带顶137meV处。

The difficulty in the fabrication of p-type ZnO hinders the development of ZnO-based devices. Group- Ⅰ and group- Ⅴ elements substituting for Zn and O can respectively form the different acceptor dopants. Park C H calculated the energy levels of different acceptor dopants in ZnO, and it is found that group- Ⅰ elements substituting for Zn are of a shallower acceptor level than group-Ⅴ elements substituting for O. Especially the aceeptor level of Li substituting for Zn （ Liz, ） is 0.09 eV, which is the shallowest value among the energy levels of acceptor dopants in ZnO reported. However, when Li atom substitutes for Zn, it will easily be accompanied by the formation of interstitial Li （ Lii ） , which is likely to be shallow donor. This causes the p-type doping to be limited by the formation of a Lizn-Lii complex donor. Based on above, Li was used as the acceptor dopant substituting for Zn in this work. In order to repress the formation of Lii, nitrogen was used as a codopant with lithium by a two step annealing process to form Lizn-N complex acceptor. The electrical and photoluminescence （PL） characteristics of p-type ZnO： Li are discussed. As comparison, the electrical and photoluminescence （PL） characteristics of the undoped ZnO grown under the same condition were also measured. By the measurement of Hall effect, it is shown that the room-temperature p-type ZnO： Li resistivity is of 678.34Ω· cm with a Hall mobility of 1.03 cm^2 · V^ -1·s^-1 and a carrier concentration of 8. 934 × 10^15 cm^-3. By the measurement of room-temperature photoluminescence （PL） , it is found that the near band-edge PL peak of p-type ZnO： Li shift to the lower energy by 23 meV than ihat of the undoped ZnO. By the measurement of low-temperature （ 12 K ） photoluminescence （ PL）, the optical level of the Lizn-N complex acceptor is estimated to be about 137 meV.