AlN插入层对AlxGa1-xN/GaN界面电子散射的影响

本文研究AlN作为Al_xGa_1-xN/GaN插入层引起的电子输运性质的变化, 考虑了Al_xGa_1-xN和AlN势垒层的自发极化、压电极化对Al_xGa_1-xN/AlN/GaN双异质结高电子迁移率晶体管(HEMT)中极化电荷面密度、二维电子气(2DEG) 浓度的影响, 分析了AlN厚度与界面粗糙度散射和合金无序散射的关系; 结果表明, 2DEG 浓度、界面粗糙度散射和合金无序散射依赖于AlN层厚度, 插入一层1–3 nm薄的AlN层, 可以明显提高电子迁移率.     

氟磷共掺杂二氧化硅光纤预制棒的表面晶化

对F、P共掺杂光纤预制棒退火后的表面晶化行为进行了研究.由改进的化学汽相沉淀法制备的氟和磷共掺杂二氧化硅光纤预制棒玻璃样品在6 h的1 150 ℃控温加热处理后,其表面发生晶化.用X-射线衍射仪观测其晶相,主要为α-方石英,可使玻璃具有二阶光学非线性;用光学显微镜观察了其表面形貌并对结晶微粒的大小进行测量,知晶粒大小在十几到几十μm之间,会造成散射损耗的增加.实验结果,还显示氟对结晶过程有很大的影响.     

Influence of a two-dimensional electron gas on current—voltage characteristics of Al0.3{Ga}0.7 N/GaN high electron mobility transistors

The J-V characteristics of AltGa1 tN/GaN high electron mobility transistors（HEMTs） are investigated and simulated using the self-consistent solution of the Schro dinger and Poisson equations for a two-dimensional electron gas（2DEG） in a triangular potential well with the Al mole fraction t = 0.3 as an example.Using a simple analytical model,the electronic drift velocity in a 2DEG channel is obtained.It is found that the current density through the 2DEG channel is on the order of 10^13 A/m^2 within a very narrow region（about 5 nm）.For a current density of 7 × 10^13 A/m62 passing through the 2DEG channel with a 2DEG density of above 1.2 × 10^17 m^-2 under a drain voltage Vds = 1.5 V at room temperature,the barrier thickness Lb should be more than 10 nm and the gate bias must be higher than 2 V.     

石墨烯中嵌入硅纳米线的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法研究了石墨烯中嵌入不同构型硅纳米线的电子特性.分析了不同构型的硅纳米线嵌入石墨烯后结构的稳定性、能带结构、态密度和差分电荷密度.研究发现:(1)直线型-I硅纳米线嵌入结构存在带隙,并且带隙的大小受到硅含量的调节.(2)扶手椅型硅纳米线嵌入结构和直线型-II硅纳米线嵌入结构由半导体变为导体.     

Population inversion study of GaAs/AlGaAs three-quantum-well quantum cascade structures

A population inversion study of GaAs/AlxGa1-x As three-quantum-well quantum cascade structures is presented. We derive the population inversion condition (PIC) of the active region (AR) and discuss the PICs on different structures by changing structural parameters such as the widths of quantum wells or barriers in the AR. For some instances, the PIC can be simplified and is proportional to the spontaneous emission lifetime between the second and the first excited states, whereas some other instances imply that the PIC is proportional to the state lifetime of the second excited state.     

Strained and Piezoelectric Characteristics of Nitride Quantum Dots

The deformation potential and piezoelectric field in nitride GaN/AIN quantum dots （QDs） are investigated in the framework of effective mass approximation （EMA） and finite element method （FEM）. The strained fields and piezoelectric characteristics are studied by using FEM for GaN/AIN QDs （GaN embedded in AIN） in the shape of truncated hexagonal pyramids. We presented the calculated results of the electronic states, wave functions, QD strain field distribution and piezoelectric effects in the QDs. Effects of spontaneous and piezoelectric polarization are taken into account in the calculation. The theoretical results are dependent on QD shapes and sizes. Some of them make the GaN/AIN QDs interesting candidates in optoelectronic applications.     

有限元法计算GaN/AIN量子点结构中的电子结构

根据有效质量理论单带模型,采用有限元方法(FEM)计算了GaN/AlN量子点结构中的电子结构,分析了应变和极化对电子结构的影响,计算了不同尺寸的量子点的能级,分析了量子点的大小对电子能级的影响.结果表明,形变势和压电势提升了电子能级,而且使简并能级分裂.随着量子点尺寸的增大,量子限制能减小,而压电势能起到更显著的作用,使电子的能级降低,吸收峰发生红移.     

单层与双层WSe2纳米片层的光致发光

采用气相沉积法制备了WSe₂二维纳米材料,对其低温光致发光谱进行了研究。结果表明：随着WSe₂层数的增加,其光致发光强度单调下降;当WSe₂层数从单层增加为双层时,其发光强度急剧下降,表明其能带结构已从直接带隙转变为间接带隙。进一步研究了双层WSe₂的变温光致发光谱,发现随着温度的升高,双层WSe₂发光峰中A峰峰位的变化基本符合半导体带隙的温度变化规律,而I峰峰位红移与温度基本成线性关系,表明双层WSe₂同时存在间接和直接跃迁,且直接跃迁和间接跃迁特性不同。     

Phase diffusion of a two-component Bose-Einstein condensates:exact and short-time solutions for arbitrary coherent spin state

We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state |θ₀,φ₀|. Analytical expression of the phase-diffusion time is presented for θ₀～π/2 case. In comparison with the symmetrical case (i.e., θ₀=π/2), we find that the diffusion process becomes slow due to the reduced atom number variance.