Self-assembled quantum dots, wires and quantum-dot lasers

Molecular beam epitaxy-grown self-assembled In(Ga)As/GaAs and InAs/InAlAs/InP quantum dots (QDs) and quantum wires (QWRs) have been studied. By adjusting growth conditions, surprising alignment. preferential elongation, and pronounced sequential coalescence of dots and wires under specific condition are realized. The lateral ordering of QDs and the vertical anti-correlation of QWRs are theoretically discussed. Room-temperature (RT) continuous-wave (CW) lasing at the wavelength of 960 nm with output power of 3.6 W from both uncoated facets is achieved fi-om vertical coupled InAs/GaAs QDs ensemble. The RT threshold current density is 218 A/cm(2). A RT CW output power of 0.6 W/facet ensures at least 3570 h lasing (only drops 0.83 dB). (C) 2001 Elsevier Science B.V, All rights reserved.

Influence of interdot electronic coupling on photoluminescence spectra of self-assembled InAs/GaAs quantum dots

The influence of interdot electronic coupling on photoluminescence (PL) spectra of self-assembled InAs/GaAs quantum dots (QDs) has been systematically investigated combining with the measurement of transmission electron microscopy. The experimentally observed fast red-shift of PL energy and an anomalous reduction of the linewidth with increasing temperature indicate that the QD ensemble can be regarded as a coupled system. The study of multilayer vertically coupled QD structures shows that a red-shift of PL peak energy and a reduction of PL linewidth are expected as the number of QD layers is increased. On the other hand, two layer QDs with different sizes have been grown according to the mechanism of a vertically correlated arrangement. However, only one PL peak related to the large QD ensemble has been observed due to the strong coupling in InAs pairs. A new possible mechanism to reduce the PL linewidth of QD ensemble is also discussed.

温带湿润区荒地潜力评价和生态建设设计－以柳河县郭家沟为例

本文采取在实验区定位研究的方式，对荒地生态系统的土壤物理性质、植被性质及荒地斑块性质与基质的关系进行了系列观测。试图在荒地斑块分类和潜力评价的基础上，确定出荒地斑块的生态建设设计方案。本文重点研究了：（1）景观变化与荒地植被演替、土壤物理性质变化之间的关系；（2）荒地斑块的土壤物理性质、植被状况及景观基质的地理特征在空间上的变异规律和以景观制图的形式对其进行表述的方法；（3）荒地斑块的稳定程度、干扰传播状况和荒地斑块对景观稳定性的影响程度；（4）荒地斑块生态建设迫切性排序、生态建设的方向、方式。本论文通过实验研究，寻求验证了小尺度下生态建设设计的核心方法：（1）斑块及景观稳定性评价方法；（2）确定各斑块生态建设方式、时间及种群配置的方法。研究结果表明，欲完成了详尽到斑块的尺度生态建设设计，必须借鉴并完善：（1）斑块划分与分类方法；（2）湿润山区的自然生产潜力评价方法；（3）生态建设的经济效益分析方法。本文最终确定出实验区的218个荒地斑块生态建设的方式和实验区生态建设时空结构。