应变纤锌矿ZnO/Mg_xZn_(1-x)O柱形量子点中离子受主束缚激子的光学性质

Optical properties of ionized acceptor-bound excitons confined in wurtzite ZnO/Mg_xZn_(1-x)O cylindrical quantum dots

在有效质量近似下,考虑内建电场效应,采用变分法详细研究了受限于纤锌矿Mg_xZn_(1-x)O/ZnO/Mg_xZn_(1-x)O圆柱形应变量子点中离子受主束缚激子(A^-,X)的带间光跃迁吸收系数随量子点尺寸、Mg含量和离子受主杂质中心位置的变化情况,并和离子施主束缚激子(D^+,X)及自由激子进行了比较.结果表明:随着量子点尺寸的减小,(A^-,X)的光跃迁吸收强度增强,吸收曲线向高能方向移动,出现蓝移现象.随着Mg含量增加,(A^-,X)的光跃迁吸收曲线蓝移,且吸收强度减弱.随着离子受主杂质从量子点的左界面沿材料生长方向移至量子点的右界面,光跃迁吸收曲线向低能方向移动,出现红移现象.此外,与离子施主束缚激子(D^+,X)相比,随着沿材料生长方向掺入杂质位置的变化,光跃迁吸收曲线移动的方向相反.但不管是掺入离子受主杂质还是离子施主杂质,当离子杂质从量子点的左异质界面沿材料生长方向移至右异质界面时,光跃迁吸收峰的移动量大致相同.

Within the framework of the single band effective -mass approximation and the dipole approximation, considering the built- in electric field due to the spontaneous and piezoelectric polarizations in wurtzite （WZ） ZnO/MgxZn1 -xO strained cylindrical quantum dots （QDs） with finite potential barriers, numerical calculations have been performed using variational procedure. The dependence of the optical absorption coefficient due to an exciton bound to an ion with charge -e （called ionized acceptor bound exciton （A- , X）） on the QD size （ height L and radius R）, Mg content x of the barrier material MgxZn1 -xO and the position of the ionized acceptor has been investigated in details. Numerical results indicate that the intensity of the optical absorption is increased and the absorption peak is moved towards the higher energy. Blue - shift is observed. Increasing Mg content causes a blue -shift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. Moreover, the absorption coefficient peak of （A- , X） complex is moved towards the lower energy and has a red - shift with moving the ionized acceptor from the left interface of QD to the right interface along the growth direction （c - axis of the WZ crystal）. In addition, the result is compared with that of ionized donor - bound exciton （D ＋ , X）, the absorption coefficient peak of （A-, X） complex is moved in the opposite direction with themovement of the ionized impurity along the growth direction. However, no matter the acceptor or donor impurity doping into ZnO QD, the movement amount of the absorption coefficient peak is same when the ionized impurity is moved from the left heterointerface of QD to the right heterointerface along the growth axis. The physical reasons for these relationships have been analyzed in depth.