空间有序的量子点超晶格的红外吸收

利用分子束外延技术,在高温下(540℃)生长了具有三维空间有序的自组织InGaAs/GaAs量子点超晶格结构,利用傅里叶变换红外光谱仪测量到了明显的垂直人射吸收峰,中心响应波长在11μm.作为对比,在低温下(480℃)生长了相同的结构,傅里叶变换红外光谱几乎没有测量到明显的垂直入射吸收峰.高分辨率X射线双晶衍射测量表明高温生长的量子点超晶格具有更好的晶体质量,原子力显微镜测量表明在高温540℃下生长的量子点具有明显的横向有序;而在低温480℃下生长的量子点并没有显示出横向有序.在进行垂直入射的吸收测量时,为了扣除量子点超晶格的周期结构带来的干涉效应,提出使用生长条件完全相同但量子点区没有掺杂的样品作为背景,提高了测量的准确性及分辨率.结果表明空间有序的量子点超晶格结构比空间无序的量子点超晶格更适宜作红外探测器结构.     

超晶格半导体材料的光磁电效应(Ⅰ)

从Shockley-read统计出发,引入载流子寿命与浓度的相关性,描述了超晶格半导体载流子的输运特征,将载流子的输运方程化为二阶非线性方程,并用双参数摄动法找到了方程的一般解.在二阶近似下,计算了半导体材料的短路电流和光导电流,进一步揭示了大信号情况下光磁电效应的非线性特征.     

Collective magnetic behavior of graphene nanohole superlattices

We predict a new class of 2-D crystalline “bulk” magnets—the graphene nanohole (GNH) superlattices with each GNH acting like a “super” magnetic atom, using first principles calculations. We show that such superlattices can exhibit long-range magnetic order above room temperature, with a collective magnetic behavior governed by inter-NH spin spin interactions in additional to intra-NH spin ordering. Furthermore, magnetic semiconductors can be made by doping magnetic NHs into semiconducting NH superlattices. The possibility of engineering magnetic GNHs for storage media and spintronics applications is discussed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Development of ultra-high density silicon nanowire arrays for electronics applications

This article reviews our recent progress on ultra-high density nanowires (NWs) array-based electronics. The superlattice nanowire pattern transfer (SNAP) method is utilized to produce aligned, ultra-high density Si NW arrays. We fi rst cover processing and materials issues related to achieving bulk-like conductivity characteristics from 10 20 nm wide Si NWs. We then discuss Si NW-based fi eld-effect transistors (FETs). These NWs & NW FETs provide terrifi c building blocks for various electronic circuits with applications to memory, energy conversion, fundamental physics, logic, and others. We focus our discussion on complementary symmetry NW logic circuitry, since that provides the most demanding metrics for guiding nanofabrication. Issues such as controlling the density and spatial distribution of both p-and n-type dopants within NW arrays are discussed, as are general methods for achieving Ohmic contacts to both p-and n-type NWs. These various materials and nanofabrication advances are brought together to demonstrate energy effi cient, complementary symmetry NW logic circuits.     

MOCVD外延Al_2O_3基AlGaN/GaN超晶格的结构和光学特性

通过X射线衍射分析、透射电镜观察、红外透射光谱分析、紫外-可见吸收光谱分析和光致发光试验,研究了用金属有机物化学汽相沉积(MOCVD)的方法,在带有GaN缓冲层的蓝宝石(Al2O3)衬底上生长的AlGaN/GaN超晶格材料的微观结构、光吸收性质和发光特性。X射线衍射结果表明,GaN基材料均为纤锌矿六方结构,薄膜具有良好的结晶质量,薄膜生长沿c轴择优取向。透射电镜观察表明,超晶格试样的周期结构分布均匀,实际周期为13.3nm,且观察到高密度的位错存在于外延膜中。通过光学试验数据,确定了试样的光学吸收边都是在370nm附近,理论计算显示试样为直接跃迁型半导体,禁带宽度约为3.4eV。试样的折射率随光子能量的增加而增加、随波长的增加而减小,计算表明消光系数的极小值位于370nm处。光致发光测试分析表明,超晶格有很好的发光性能,并发现存在黄带发光。     

定数截尾数据缺失场合下k（m）/n系统可靠性指标的Bayes估计

在定数截尾缺失数据样本下,研究了不可修中取串连续失效系统（简记为k（m）/n系统）的可靠性评估问题。利用Bayes方法得到了部件的平均寿命、系统可靠度及平均寿命等可靠性指标的Bayes估计。最后利用随机模拟例子说明了本文方法的正确性和可行性。     

Reduced light sensitivity and persistent photoconductivity in novel modulation doped heterostructures incorporating an n·GaAs/AlGaAs superlatt1ce as the high bandgap material

A short period 15 Å/15 Å GaAs/Al_xGa_1?xAs superlattice where only the GaAs layers are doped with Si donors has been incorporated in a GaAs/Al_xGa_1?xAs molecular beam epitaxial modulation doped heterostructure in place of the doped high bandgap ternary alloy. The removal of the donors from the Al_xGa_1?xAs eliminates the component of light sensitivity resulting from the deep persistent photoconductivity (PPC) traps present in this material. This results in a reduction in overall light sensitivity and an elimination of the PPC effect at 77K.     

Interband magneto-absorption in narrow-gap HgTe/CdTe superlattice structures

The use of a magnetic field for interband absorption experiments in the midinfrared regime can reveal the electronic band structure of HgTe/CdTe superlattices. In high-quality samples pronounced magnetic field-induced absorption peaks are observed in the transmission spectra due to hole to electron Landau level transitions. By extrapolating the excitation energies for such transitions to B = 0, gap energies between several hole and electron subbands can be determined accurately. In addition, we show that interband magnetoabsorption provides a sensitive feedback for growth of quantum structures.     

新型电子器件和光学器件的共振隧穿结构

描述了一种新型共振隧穿结构器件，这种器件包含了通过可变间隙超晶格能量滤波器（ＶＳＳＥＦ）中的耦合量子附态的隧穿过程．论证了通过ＡｌＡｓ／ＧａＡｓＶＳＳＥＦ器件高能态和ＡｌＧａＡｓ／ＧａＡｓ超晶格受激态的共振隧穿，描述了这种器件作为较高功率微波源和共振隧穿晶体管的应用，并讨论了共振隧穿结构作为雪崩探测器和红外发射器等光学器件的潜在应用．     

Layer intermixing and related long-term instability in heavily carbon-doped AlGaAs/GaAs superlattices

Superlattices (SLs) of Al_o.3Ga_o.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CClp₄ were annealed for 24 h at 825° C under a variety of ambient and surface encapsulation conditions. Photoluminescence atT = 1.7 K has been employed to determine approximate Al-Ga interdiffusion coefficients (D _Ai-Ga) for different annealing conditions. For all encapsulants studiedD _Al-Ga increases with increasing As₄ pressure in the annealing ampoule. This result disagrees with trends reported for Mg-doped crystals, and with predictions of the charged point-defect (Fermilevel) model. The Si₃N₄ cap provides the most effecitve surface sealing against ambientstimulated layer interdiffusion (D _Al-Ga ≈ 1.5-3.9 x 10^-19 cm²/sec). The most extensive layer intermixing has occurred for an uncapped SL annealed under As-rich ambient (D _Al-Ga ≈ 3.3 x 10^-18 cm²/sec). These values are up to ~40 times greater than those previously reported for nominally undoped AIGaAs/GaAs SLs, implying that theC _As doping slightly enhances layer intermixing, but significantly less than predicted by the Fermi-level effect. The discrepancies between the experimental data and the model are discussed. Pronounced changes in the optical properties of the annealed SLs with storage time at room temperature are also reported. These changes may indicate a degraded thermal stability of the annealed crystals due to high-temperature-induced lattice defects. A possibly related effect of the systematic failure to fabricate buried heterostructure quantum well lasers via impurity-induced layer disordering in similarly doped AIGaAs/GaAs crystals is discussed.