磁场下半导体GaAs/AlxGa1-xAs异质结中的杂质态

对异质结势采用三角势近似,考虑屏蔽效应,用变分法讨论磁场下半导体异质结系统中的施主杂质态,数值计算了GaAs/AlxGa_1-xAs单异质结系统中杂质态结合能随磁场的变化关系。结果表明,由于外界磁场使界面附近束缚于正施主杂质的单电子波函数的定域性增强,从而对杂质态的结合能有明显的影响,结合能随磁感应强度的增强而显著增大。还计算了杂质位置、电子面密度产生的导带弯曲以及屏蔽效应诸因素对结合能的影响。结果显示,结合能对电子面密度和杂质位置的变化十分敏感,屏蔽则使得有效库仑吸引作用减弱而导致结合能明显下降。

Impurity States in Semiconductor GaAs/AlxGa1-xAs Heterojunctions with an External Magnetic Field

In recent years,the experimental advance has stimulated interest in semiconductor quantum wells and heterojunctions to explore the novel phenomena and their applications.Some authors investigated the shallow donors in quantum well with presence of a magnetic field.But few studies focused on the states of impurities near the heterojunction interface with the external magnetic field,especially in consideration of the electronic screening effect.A variational method is adopted to investigate the binding energies of shallow donor impurities near the interface of a single semiconductor heterojunction system in the presence of a static uniform magnetic field by considering a triangular potential to approximate the interface potential.The electronic image potential and the screened Coulombic impurity potential are also taken into account to investigate the impurity state binding energy.Numerical computation has been performed for the GaAs/Al_xGa_1-xAs structure.For a given impurity position the binding energy as a function of magnetic field,perpendicular to the interface,shows a monotonic increase tendency with increasing the magnetic field strength B,which makes the electronic wave functions highly localized to magnify the effective Coulombic attraction.This monotonic property is different from the maximum property obtained by Hollox.The binding energy is also computed as a function of the impurity position z₀ to show that the binding energy increases at first,and then decreases with increasing the distance between the impurity and the interface.The results corresponding to with and without the screening effect are compared.It is found that even in the presence of a magnetic field the screening effect dramatically decreases the impurity state binding energy,which is obviously influenced by the barrier potential and the conduction band bending.The binding energy is sensitive to the areal electron density.It is also found that the influence of the electron image potential is negligibly small so that it needs to be considered in the further discussion.This is consistent with the early conclusion for without a magnetic field case.