论文标题:磁场下异质结系统中的杂质态和束缚极化子及温度与压力效应
Impurity States and Bound Polarons in Heterojunctions under Magnetic Field and the Temperature, Pressure Effects
论文作者 张敏
论文导师 班士良,论文学位 硕士,论文专业 凝聚态物理
论文单位 内蒙古大学,点击次数 94,论文页数 38页File Size1188k
2004-05-15论文网 http://www.lw23.com/lunwen_521236872/ 半导体异质结,杂质态,极化子,结合能,磁场,温度,压力
Semiconductor heterojunction, Polaron, Binding energy, Magnetic field, temperature, pressure
本文对异质结势采用三角势近似，讨论磁场下半导体异质结中电子气对施主杂质态结合能的影响、声子对束缚极化子结合能的影响。采用实际异质结势，讨论半导体异质结中自由极化子自陷能的温度与压力效应。 对GaAs／Al_xGa_(1-x)As异质结，采用三角势近似异质结势，考虑外界恒定磁场以及电子气的屏蔽对施主杂质单电子基态能量的影响。结果表明：杂质态结合能随磁场的增强而显著增大。结合能随杂质位置、电子面密度的变化趋势与无磁场时相同。存在磁场时，屏蔽效果仍然十分显著，明显降低了杂质态的结合能，结合能随杂质位置、电子面密度的变化趋势与无屏蔽的结果相同。 对该异质结，考虑体纵光学声子和两支界面声子的影响，利用改进的LLP中间耦合方法处理电子-声子相互作用和杂质-声子相互作用，计算了极化子结合能随磁场强度、杂质位置和电子面密度的变化关系。结果表明：极化子结合能随磁场呈现增加的趋势，LO声子对结合能的负贡献受磁场的影响显著，而IO声子的负贡献受磁场的影响并不显著。另外，三角势的选取说明：导带弯曲不容忽视。还须指出的是，电子像势对结合能的影响很小，可以忽略。 对GaN／Al_xGa_(1-x)N异质结，采用实际异质结势，同时计入体纵光学声子和两支界面声子，考虑温度及流体静压力对自由极化子自陷能和有效质量的影响，用变分法计算了异质结系统中极化子自陷能和有效质量随温度、压力、电子面密度以及Al组分的变化关系。结果表明：压力对异质结诸参数的综合作用导致自由极化子的自陷能随压力呈近线性显著增加。温度效应则使极化子自陷能明显降低，向近自由电子蜕变。同时，压力和温度对极化子的有效质量也有较大影响，其趋势与自陷能的变化相同。
In this paper, the ground state binding energy of an electron bound to a positively charged donor impurity near the interface of a semiconductor heterojunction with a triangular potential approximation is investigated by considering the electron-gas screening effect under an external magnetic field. Furthermore, the phonon and magnetic field influence on the bound polaron is discussed. A realistic heterojunction potential is adopted to study the temperature and pressure effect on the self-trapping energy of a free polaron in a semiconductor heterojunction.In a GaAs/AlxGa1-xAs heterojunction, the triangular potential approximation is used to investigate the influences of an external static uniform magnetic field and the electron-gas screening on the ground state binding energy of an impurity with a single electron. It is found that the impurity binding energy increases obviously with the magnetic field. The trend of the binding energy as a function of impurity position and electron areal density is the same as the result without a magnetic field. It is also found that the screening influence on the binding energy is also obviously when there is an external magnetic field, which reduces dramatically the binding energy. The trend of the binding energy as a function of impurity position and electron areal density is the same as the result without screening.. For the heterojunction, a modified LLP variational method is adopted to calculate the bound polaron binding energy as a function of the magnetic field, impurity position and electron areal density. The influences of the electron-phonon and impurity-phonon interaction including the effect of half-space bulk longitudinal and interface-optical phonon modes are considered. It is found that the bound polaron binding energy shows a monotonic increase tendency with increasing the magnetic field strength. The contribution from bulk longitudinal optical phonons to the binding energy obviously increases as the impurity being near the interface. It is also proved that the conductive band bending should not be neglected. Furthermore, it should be pointed out that the influence of the electron image potential is negligibly small so that it can be neglected in the further discussion.For a GaN/AlxGa1-xN heterojunction, a variational method and a realistic heterojunction potential are adopted to obtain the dependencies of the polaron self-trapping energy and theeffective mass on temperature, pressure, electron areal density and Al concentration by considering the temperature and the hydrostatic pressure effect, including the effect of half-space bulk longitudinal and interface-optical phonon modes. It is found that the pressure comprehensive effect on the heterojunction factors induces the free polaron self-trapping energy to increase near linearly with pressure. On the other hand, the temperature effect make the polaron self-trapping energy decrease obviously so that the polaron becomes free-electron-like as temperature increases. The pressure and temperature influence distinctly on the polaron effective mass with a trend similar to that the self-trapping energy shows.
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