Delay of the excited state lasing of 1310 nm InAs/GaAs quantum dot lasers by facet coating

In this letter, we present a facet coating design to delay the excited state (ES) lasing for 1310 nm InAs/GaAs quantum dot lasers. The key point of our design is to ensure that the mirror loss of ES is larger than that of the ground state by decreasing the reflectivity of the ES. In the facet coating design, the central wavelength is at 1480 nm, and the high- and low-index materials are Ta2O5 and SiO2, respectively. Compared with the traditional Si/SiO2 facet coating with a central wavelength of 1310 nm, we have found that with the optimal design the turning temperature of the ES lasing has been delayed from 90 to 100 degrees C for the laser diodes with cavity length of 1.2 mm. Furthermore, the characteristic temperature (T-0) of the laser diodes is also improved.

复杂无机离子晶体晶格能的研究

对于简单二元晶体（I-VII，II-VI，III-V族晶体），我们发现了它们的晶格能、德拜温度、等离子体能量、体变模量间的一些简单关系，分析发现了德拜模型的局限性，得到离子品体晶格能最小可能值为546kjmol-1，也发现碱金属卤化物的晶格能与格波的纵、横光学支的波数都呈线性关系，相同阳离子及相同阴离子的碱金属卤化物的LEELS、HEELS，ORS的谱峰能量值也与晶格能呈线性关系，说明这些量都与离子间的｛妾合强度有一定的关系。基于复杂靛．体化学键介电理论，并考虑到晶格能和键性的关系，我们发展了一种新的经验地计算晶．格能的方法，晶格能被视为是由各类键贡献的，对于每类键，其对晶格能的贡献被分为离子性和共价性两部分，复杂离子晶体被分解后得到的各类键可做相似处理。我们又基于Born理论模型，考虑到离子晶体中离子间主要作用是库仑作用及电子壳层的排斥作用，发展了另一种简单的计算晶格能的方法。对于很多静电键为主的功能材料（如巨磁阻材料、超导体等），用这两种方法计算的晶格能值与实验值及他人的计算结果相当接近，它们可以作为复杂离子晶体晶格能可信I均估算方法。我们还计算了YBCO体系的晶格能，并得到其与氧浓度的函数关系。

分光光度法测定钛和钒的价态

本论文“分光光度法则测定钛和钒的价态”包括互相独立的两部分工作：一、关于钛，经比较选用2－噻吩甲酰三氟丙酮作为Ti(III)的显色剂。在含二氯化锡的盐酸介质中，形成具有M:R = 1:3的稳定络合物，在685和485nm处有两个吸收峰，摩尔吸光系数分别为1.10 * 10~3和1.79 * 10~3。在685nm处测定Ti(III)有很高的选择性，百倍量的Ti(IV)和除氧化剂外的毫克量的多数常见离子无影响。0－300微克Ti(III)/10毫升范围内遵守比尔定律。应用本法测定了三氯化钛氧化剂和异丙橡胶中的Ti(III)和Ti(IV)。另外建立了新的配制和保存Ti(III)标准溶液的方法。二、关于钒、用磷钼杂多酸－罗丹明B作试剂，在存在聚乙烯醇的情况下，水相分光光度测定了三、四、五价钒。V（▽）与试剂形成四元络合物R_4[Mo_(11)V(▽)PO_(40)], V(IV)无显色反应，V(III)还原磷钼杂多酸成磷钼等，再与罗凡明B形成三元络合物R_5[Mo_(10)(VI)Mo_2(▽)PO_(40)]，过剩磷钼杂多酸由加入柠檬酸掩蔽。当V(IV)与V(▽)共存时，将其氧化成V(▽)，测合量后减去V(▽)而得V(IV)含量；当V(IV)与V(III)共存时，将其还原成V(III)，测合量后减去V(III)而得V(IV)含量。试剂最大吸收峰在555nm，两种络合物最大吸收峰都在586nm处，络合物的摩尔吸光系数分别为2.80 * 10~5和2.16 * 10~5。0-3.0微克V(▽)和0-4.0微克V(III)/25毫升遵守比尔定律。仅钛、锆、铌和钽及氧化、还原剂有影响。一个体系能高灵敏的测定三、四、五价钒，本工作还是首次。

砷的化学形态分析方法的研究

本论文由三部分组成。第一部分是天然水中痕量砷（III）和无机砷总量的测定。我们提出了用硼氢化钾片作还原剂，在柠檬酸铵介质中选择还原砷（III），在洒石酸介质中还原无机砷总量，还原生成的砷化氢与同时生成的氢气一起通过吸收液显色，再用分光光度计分别测定砷（III）和无机砷总量的分析方法，并且对几种天然水样进行了分析和标准加入加收试验。本方法具有较好的精密度和较高的灵敏度，砷（III）的检出限为0.16ppb，无机砷总量的检出限为0.36ppb，而且分析速度快，操作简便，易于推广。第二部分是无机砷和有机胂的分离与测定。我们选用砷（III）和砷（v-bar）代表无机砷，二甲基胂酸和苯基胂酸代表有机胂，利用氢氧化铁对无机砷和有机胂的共沉淀能力的差异分离无机砷和有机胂，再用高氯酸—硝酸消化有机胂，以分光光度法分别测定。通过对水、土壤，特别是药物样品的分析，并把分析结果与高氯酸—硝酸消化测定的总砷量进行比较表明，本方法确实具有很好的实用价值。该方法的建立对于一些含砷量高的药物建立除砷方法和砷对人体毒害机理的进一步研究具有重要的意义。第三部分是对氢氧化铁吸附砷机理的探讨。文中讨论了氢氧化铁吸附砷的机制，认为溶液中砷离子是与不同水解度的铁的羟基化合物形成了离子缔合物而被氢氧化铁共沉淀的。同时观察到，随着砷的形态不同，氢氧化铁对它们的吸附能力也不相同。通过比较几种氢氧化物对不同形态砷吸附能力的差异和氢氧根离子对吸附能力的影响等试验，初步证明，三价铁离子水解过程中的某些产物以及不同形态砷离子的空间构型的氢氧化铁吸附不同形态砷的能力解产生很大的影响。文中还通过实验，确定了氢氧化铁吸附砷（III）和砷（v-bar）的等温吸附经验公式中的常数，并对砷（III）和砷（v-bar）在氢氧化铁上的吸附速率作了比较和讨论。

稀磁半导体的研究进展

本文主要介绍了III-V族稀磁半导体(Ga,Mn)As的研究进展,包括(Ga,Mn)As的生长制备、基本磁性质、磁输运特征、磁光性质、磁性起源、相关的异质结构和自旋注入等,同时还简单介绍了其它稀磁半导体如IV族、III-VI族和IV-VI族等稀磁半导体的研究进展,在文章的最后描述了理想的稀磁半导体应该具备的特征以及对未来的展望。

（111）A InP衬底上MOCVD外延InGaAsP的表面形貌和光学特性

为了研究(111)衬底的特性以及实现等边三角形微腔激光器，利用金属有机化学气相淀积(MOCVD)研究了(111)A InP衬底上InGaAsP外延层的表面形貌和光学特性。考虑到(111)A InP衬底的悬挂键密度比较低，在生长过程中有意提高了V／III比。通过扫描电子显微镜(SEM)和光荧光(PL)谱分别研究了外延层的表面形貌和光学特性。实验发现，表面形貌和光学特性随V／III比和温度的变化非常大。最佳V／IlI比和温度分别为400和625℃。

同步辐射光电子能谱研究室温下Na对InP（100）表面氮化反应的影响

利用同步辐射光电子能谱研究了室温下Na吸附下于P型InP(100)表面对其氮化反应的影响,通过P2p、In 4d芯能级谱的变化,对Na/InP(100)表面的氮化反应的研究表明,碱金属Na的吸附对InP(100)无明显的催化氮化作用,即使采用N_2/Na/N_2/Na/N_2/Na/InP(100)的类多层结构,在室温下也只有极少量的氮化物形成,而无明显的催化氮化反应发生.碱金属吸附层对III-V族半导体氮化反应的催化机制不同于碱金属对于元素半导体的催化反应机制,碱金属对元素半导体的催化氮化反应,吸附的碱金属与元素半导体衬底之间无需界面反应发生,而碱金属吸附层和III-V族半导体衬底之间发生界面反应而形成的表面缺陷在III-V族半导体的催化氮化反应过程中具有重要的作用.

Effects of polarization field on formation of two-dimensional electron gas in (0001) and (11(2)over-bar0) plane AlGaN/GaN heterostructures

Photoluminescence (PL) and temperature-dependent Hall effect measurements were carried out in (0001) and (11 (2) over bar0) AlGaN/GaN heterostructures grown on sapphire substrates by metalorganic chemical vapor deposition. There are strong spontaneous and piezoelectric electric fields (SPF) along the growth orientation of the (0001) AlGaN/GaN heterostructures. At the same time there are no corresponding SPF along that of the (1120) AlGaN/GaN. A strong PL peak related to the recombination between two-dimensional electron gas (2DEG) and photoexcited holes was observed at 3.258 eV at room temperature in (0001) AlGaN/GaN heterointerfaces while no corresponding PL peak was observed in (11 (2) over bar0). The existence of a 2DEG was observed in (0001) AlGaN/GaN multi-layers with a mobility saturated at 6000 cm(2)/V s below 80 K, whereas a much lower mobility was measured in (11 (2) over bar0). These results indicated that the SPF was the main element to cause the high mobility and high sheet-electron-density 2DEG in AlGaN/GaN heterostructures. (C) 2004 Elsevier B.V. All rights reserved.

Orientation relationship between hexagonal inclusions and cubic GaN grown on GaAs(001) substrates

Cubic GaN/GaAs(0 0 1) epilayers and hexagonal inclusions are characterized by X-ray diffraction (XRD), Photoluminescence (PL), Raman spectroscopy, and transmission electron microscopy (TEM). The X-ray {0 0 0 2} and (1 0 (1) over bar 0) pole figures show that the orientation relationships between cubic GaN and hexagonal inclusions are (1 1 1)//(0 0 0 1), <1 1 2 >//<1 0 (1) over bar 0 >. The distribution of hexagonal inclusions mainly results from the interfacial bonding disorder in the grain boundaries parallel to hexagonal <0 0 0 1 > directions and the lattice mismatch in <0 0 0 1 > directions on {1 0 (1) over bar 0} planes. In order to reduce the energy increase in cubic epilayers, hexagonal lamellas with smaller sizes in <0 0 0 1 > directions often nucleate inside the buffer layer or near the interface between the buffer layer and the epitaxial layer, and penetrate through the whole epitaxial layer with this orientation relationship. (C) 2001 Elsevier Science B.V. All rights reserved.

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.

Hybrid integration and packaging of grating-coupled silicon photonics

This thesis covers both the packaging of silicon photonic devices with fiber inputs and outputs as well as the integration of laser light sources with these same devices. The principal challenge in both of these pursuits is coupling light into the submicrometer waveguides that are the hallmark of silicon-on-insulator (SOI) systems. Previous work on grating couplers is leveraged to design new approaches to bridge the gap between the highly-integrated domain of silicon, the Interconnected world of fiber and the active region of III-V materials. First, a novel process for the planar packaging of grating couplers with fibers is explored in detail. This technology allows the creation of easy-to-use test platforms for laser integration and also stands on its own merits as an enabling technology for next-generation silicon photonics systems. The alignment tolerances of this process are shown to be well-suited to a passive alignment process and for wafer-scale assembly. Furthermore, this technology has already been used to package demonstrators for research partners and is included in the offerings of the ePIXfab silicon photonics foundry and as a design kit for PhoeniX Software’s MaskEngineer product. After this, a process for hybridly integrating a discrete edge-emitting laser with a silicon photonic circuit using near-vertical coupling is developed and characterized. The details of the various steps of the design process are given, including mechanical, thermal, optical and electrical steps. The interrelation of these design domains is also discussed. The construction process for a demonstrator is outlined, and measurements are presented of a series of single-wavelength Fabry-Pérot lasers along with a two-section laser tunable in the telecommunications C-band. The suitability and potential of this technology for mass manufacture is demonstrated, with further opportunities for improvement detailed and discussed in the conclusion.

Development of germanium/silicon integration for near infrared detection

Silicon (Si) is the base material for electronic technologies and is emerging as a very attractive platform for photonic integrated circuits (PICs). PICs allow optical systems to be made more compact with higher performance than discrete optical components. Applications for PICs are in the area of fibre-optic communication, biomedical devices, photovoltaics and imaging. Germanium (Ge), due to its suitable bandgap for telecommunications and its compatibility with Si technology is preferred over III-V compounds as an integrated on-chip detector at near infrared wavelengths. There are two main approaches for Ge/Si integration: through epitaxial growth and through direct wafer bonding. The lattice mismatch of ~4.2% between Ge and Si is the main problem of the former technique which leads to a high density of dislocations while the bond strength and conductivity of the interface are the main challenges of the latter. Both result in trap states which are expected to play a critical role. Understanding the physics of the interface is a key contribution of this thesis. This thesis investigates Ge/Si diodes using these two methods. The effects of interface traps on the static and dynamic performance of Ge/Si avalanche photodetectors have been modelled for the first time. The thesis outlines the original process development and characterization of mesa diodes which were fabricated by transferring a ~700 nm thick layer of p-type Ge onto n-type Si using direct wafer bonding and layer exfoliation. The effects of low temperature annealing on the device performance and on the conductivity of the interface have been investigated. It is shown that the diode ideality factor and the series resistance of the device are reduced after annealing. The carrier transport mechanism is shown to be dominated by generation–recombination before annealing and by direct tunnelling in forward bias and band-to-band tunnelling in reverse bias after annealing. The thesis presents a novel technique to realise photodetectors where one of the substrates is thinned by chemical mechanical polishing (CMP) after bonding the Si-Ge wafers. Based on this technique, Ge/Si detectors with remarkably high responsivities, in excess of 3.5 A/W at 1.55 μm at −2 V, under surface normal illumination have been measured. By performing electrical and optical measurements at various temperatures, the carrier transport through the hetero-interface is analysed by monitoring the Ge band bending from which a detailed band structure of the Ge/Si interface is proposed for the first time. The above unity responsivity of the detectors was explained by light induced potential barrier lowering at the interface. To our knowledge this is the first report of light-gated responsivity for vertically illuminated Ge/Si photodiodes. The wafer bonding approach followed by layer exfoliation or by CMP is a low temperature wafer scale process. In principle, the technique could be extended to other materials such as Ge on GaAs, or Ge on SOI. The unique results reported here are compatible with surface normal illumination and are capable of being integrated with CMOS electronics and readout units in the form of 2D arrays of detectors. One potential future application is a low-cost Si process-compatible near infrared camera.

High speed nonlinear optical components for next-generation optical communications

Electronic signal processing systems currently employed at core internet routers require huge amounts of power to operate and they may be unable to continue to satisfy consumer demand for more bandwidth without an inordinate increase in cost, size and/or energy consumption. Optical signal processing techniques may be deployed in next-generation optical networks for simple tasks such as wavelength conversion, demultiplexing and format conversion at high speed (≥100Gb.s-1) to alleviate the pressure on existing core router infrastructure. To implement optical signal processing functionalities, it is necessary to exploit the nonlinear optical properties of suitable materials such as III-V semiconductor compounds, silicon, periodically-poled lithium niobate (PPLN), highly nonlinear fibre (HNLF) or chalcogenide glasses. However, nonlinear optical (NLO) components such as semiconductor optical amplifiers (SOAs), electroabsorption modulators (EAMs) and silicon nanowires are the most promising candidates as all-optical switching elements vis-à-vis ease of integration, device footprint and energy consumption. This PhD thesis presents the amplitude and phase dynamics in a range of device configurations containing SOAs, EAMs and/or silicon nanowires to support the design of all optical switching elements for deployment in next-generation optical networks. Time-resolved pump-probe spectroscopy using pulses with a pulse width of 3ps from mode-locked laser sources was utilized to accurately measure the carrier dynamics in the device(s) under test. The research work into four main topics: (a) a long SOA, (b) the concatenated SOA-EAMSOA (CSES) configuration, (c) silicon nanowires embedded in SU8 polymer and (d) a custom epitaxy design EAM with fast carrier sweepout dynamics. The principal aim was to identify the optimum operation conditions for each of these NLO device configurations to enhance their switching capability and to assess their potential for various optical signal processing functionalities. All of the NLO device configurations investigated in this thesis are compact and suitable for monolithic and/or hybrid integration.

Dilute nitride semiconductors : band structure, scattering and high field transport

The substitution of a small fraction x of nitrogen atoms, for the group V elements in conventional III-V semiconductors such as GaAs and GaSb strongly perturbs the conduction band of the host semiconductor. In this thesis we investigate the effects of nitrogen states on the band dispersion, carrier scattering and mobility of dilute nitride alloys. In the supercell model we solve the single particle Hamiltonian for a very large supercell containing randomly placed nitrogen. This model predicts a gap in the density of states of GaNxAs1−x, where this gap is filled in the Green’s function model. Therefore we develop a self-consistent Green’s function (SCGF) approach, which provides excellent agreement with supercell calculations and reveals a gap in the DOS, in contrast with the results of previous non-self-consistent Green’s function calculations. However, including the distribution of N states destroys this gap, as seen in experiment. We then examine the high field transport of carriers by solving the steadystate Boltzmann transport equation and find that it is necessary to include the full distribution of N levels in order to account for the small, low-field mobility and the absence of a negative differential velocity regime observed experimentally with increasing x. Overall the results account well for a wide range of experimental data. We also investigate the band structure, scattering and mobility of carriers by finding the poles of the SCGF, which gives lower carrier mobility for GaNxAs1−x, compared to those already calculated, in better agreement with experiments. The calculated optical absorption spectra for InyGa1−yNxAs1−x and GaNxSb1−x using the SCGF agree well with the experimental data, confirming the validity of this approach to study the band structure of these materials.

Synthesis and reactivity of pyridine substituted α-diazocarbonyl compounds and exploration of rhodium carboxylates as asymmetric catalysts

The primary objective of this thesis was the preparation of a series of pyridine-containing α-diazocarbonyl compounds and subsequent investigation of the reactivity of these compounds on exposure to transition metal catalysts. In particular, the reactivity of the pyridyl α-diazocarbonyls was compared to that of the analogous phenyl α-diazocarbonyl compounds to ascertain the impact of replacement of the phenyl ring with pyridine. The first chapter initially provides a brief introduction into α-diazocarbonyl chemistry, comprising a compendium of well-established and recently developed methods in the preparation of these compounds, as well as an outline of the reactivity of these versatile substrates. The substantive element of this introductory chapter comprises a detailed review focused on transition metal-catalysed transformations of heterocyclic α-diazocarbonyl compounds, highlighting the extraordinary diversity of reaction products which can be accessed. This review is undertaken to set the work of this thesis in context. The results of this research are discussed in the second and third chapters together with the associated experimental details, including spectroscopic and analytical data obtained in the synthesis of all compounds during this research. The second chapter describes the preparation of a range of novel pyridine-containing α-diazocarbonyl compounds via a number of synthetic strategies including both acylation and diazo transfer methodologies. In contrast to the phenyl analogues, the generation of the pyridine α-diazocarbonyl substrates was complicated by a number of factors including the inherent basicity of the pyridine ring, tautomerism and existence of rotamers. Rhodium- and copper-mediated transformations of the pyridine-containing α-diazocarbonyl compounds is discussed in detail displaying very different reactivity patterns to those seen with the phenyl analogues; oxidation to 2,3- diketones, 1,2-hydride shift to form enones and oxonium and sulfonium ylide formation/rearrangement are prominent in the pyridyl series, with no evidence of aromatic addition to the pyridine ring. The third chapter focuses on exploration of novel chiral rhodium(II) catalysts, developed in the Maguire team, in both intermolecular cyclopropanations and intramolecular C–H insertion reactions. In this chapter, the studies are focused on standard α-diazocarbonyl compounds without heteroaryl substituents. The most notable outcome was the achievement of high enantiopurities for intramolecular C–H insertions, which were competitive with, and even surpassed, established catalyst systems in some cases. This work has provided insight into solvent and temperature effects on yields as well as enantio- and diastereoselectivity, thereby providing guidance for future development and design of chiral rhodium carboxylate catalysts. While this is a preliminary study, the significance of the results lie in the fact that these are the first reactions to give substantial asymmetric induction with these novel rhodium carboxylates. While the majority of the α-diazocarbonyl compounds explored in this work were α-diazoketones, a number of α-diazoesters are also described. Details of chiral stationary phase HPLC analysis, single crystal analysis and 2D NMR experiments are included in the Appendix (Appendix III-V).