纤锌矿结构ZnO中定位Ga-N共掺杂对p型掺杂效率的影响

Effects of Site-selective Ga-N Codoping on p-type Doping Efficiency of Wurtzite ZnO

采用第一性原理和密度泛函理论的方法,计算未掺杂、N单掺杂和Ga-N共掺杂纤锌矿结构ZnO的总能、电荷密度和能带结构。总能计算表明,Ga原子的共掺杂使总能极大地降低,从而显著提高杂质N原子在ZnO中的稳定性。电荷密度分布显示,总能的降低主要是Ga-N共掺杂后Ga原子的3d态和N原子的2p态电子之间的强杂化相互作用所致。特别是在Ga原子的负电荷和N原子的正电荷沿c轴排成一线的共掺杂构型中,较大的局域极化场的变化引起价带顶向禁带中的大分裂,降低了N受主的激活能,将空穴的浓度提高了三个量级,有效地提高p型掺杂效率。

ZnO has become a promising material for ultraviolet light emitting diodes and lasers, transparent high power electronic devices dut to their wide direct band gap and large exciton binding energy. Undoped ZnO exhibits intrinsic n-type Conductivity, and it is, therefore, difficult to achieve p-type ZnO. Among group-V dopants, N is considered to be a shallow p-type impurity; however, there are still many difficulties for using N as dopant. Recently, much effort has been devoted to fabricate p-type ZnO with codopants. So it is important to understand the codoping effect on electronic structures of wurtzite ZnO. N dopant stability and p-type doping efficiency of wurtzite ZnO were investigated by calculating the total energies, charge densities and band structures. The differences of total energy between the undoped configuration and N mono-doped, Ga-N codoped configuration Ⅰ and Ⅱ are △ET-N = 1.22 eV, △ET-Ⅰ = - 2.89 eV and △ET-Ⅱ = -2.84 eV, respectively. This shows that the N dopant stability is improved by Ga codopant. This resuit is attributable to the strong hybridization between the Ga 3d and N charge density differences. Furthermore, the polarization is significantly ch 2p states according to the induced anged in the Ga-N codoped configu- ration Ⅱ where the negative charges of the Ga atom and the positive charges of the N atom align along the c-axis. The energy band structures are thus clearly influenced. The twofold-degenerate Г5v level of the top of the valence band for undoped ZnO splits into Г9v and Г^（1）7v levels and shifts into the band gap to further separate with the non-degenerate Г1v level （labelled as Г（2）7v）. Then the activation energy of the N acceptor is lowered due t2o the splitting of the top of the valence band. Finally, according to the relationship between the hole concentration and the activation energy, the hole concentration under the modulation of configuration Ⅱ is enhanced more than three orders of magnitude.