我们研究了Al Ga As/Ga As不对称阶梯形量子阱中准二维电子气的集体激发色散关系随电场的变化特性。发现正向电场会使子带间等离激元模变短甚至消失,反向电场会使子带间等离激元模变变长。该子带间集体激发模波矢的有效大小取决于最低两能级的波函数交叠程度。这些特性可能有利于研究基于电场效应的阶梯形量子阱结构的器件。
We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.
用无规相近似的二子带模型,系统研究了阶梯层宽度、深阱宽度、阶梯层的Al组分(阶梯层势垒的高度)对Al Ga As/Ga As不对称阶梯型量子阱中准二维电子气的等离激元特性的影响。发现子带间等离激元模的能量大小取决于基态和第一激发态的能级差,而模的长短取决于这两个能级波函数的交叠大小。这些结论可能为研究空间不对称效应对准二维电子气特性的影响以及基于阶梯型量子阱结构的器件应用等方面提供有益的参考。
The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.
A new three-layer hot-wall horizontal flow metal-organic chemical vapor deposition （MOCVD） reactor is proposed. When the susceptor is heated, the temperature of the wall over the susceptor also increases to the same temperature. Furthermore, the flowing speed of the top layer is also increased by up to four times that of the bottom layer. Both methods effectively decrease the convection and make most of the metal organic （MO） gas and the reactive gas distribute at the bottom surface of the reactor. By selecting appropriate shapes, sizes, nozzles array, and heating area of the walls, the source gases are kept in a laminar flow state. Results of the numeric simulation indicate that the nitrogen is a good carrier to reduce the diffusion among the precursors before arriving at the substrate, which leads to the reduction ofpre-reaction. To get a good comparison with the conventional MOCVD horizontal reactor, the two-layer horizontal MOCVD reactor is also investigated. The results indicate that a two- layer reactor cannot control the gas flow effectively when its size and shape are the same as that of the three-layer reactor, so that the concentration distributions of the source gases in the susceptor surface are much more uniform in the new design than those in the conventional one.
The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine＇s random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode（with an energy of 12 meV（～ 3 THz）） becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.
