650nm AlGaInP quantum well lasers for the application of DVD

Main application of 650nm band laser diodes are for digital versatile disk (DVD). We demonstrate here the 650nm AlGaInP LD grown by LP-MOCVD with the structure of selected buried ridge waveguide. Excellent performance of LD have been achieved such as threshold current, threshold current density as low as 20mA and 350A/cm(2) respectively at room temperature, the operating temperature up to 90 for the linear power output of 5mw. RIN is about -130db/Hz, The samples of LD have been certified by PUH manufacturers.

High brightness AlGaInP orange light emitting diodes

Orange AlGaInP high brightness light emitting diodes (LEDs) were fabricated by low pressure metalorganic chemical vapor deposition(LP-MOCVD) technology. AlGaInP double heterojunction structure was used as active layer. 15 pairs of Al0.5Ga0.5As/AlAs distributed Bragg reflector and 7 mu m Al0.8Ga0.2As current spreading layer were employed to reduce the absorption of GaAs substrate and upper anode respectively. At 20mA the LEDs emitting wavelength was between 600-610nm with 18.3nm FWHM, 0.45mW radiation power and 1.7% external quantum efficiency. Brightness of the LED chips and LED lamps with 15 degrees viewing angle(2 theta(1/2)) reached 30mcd and 1000mcd respectively.

Growth and characterization of GaN on LiGaO2 and LiAlO2

The nearly lattice-matched LiGaO2 and LiAlO2 substrates have been used for the growth of GaN by LP-MOVPE. GaN epilayers have been grown on the two substrates at very low input partial pressure of hydrogen and relatively low growth temperature. The difference in the growth rate, crystal and optical qualities of hexagonal GaN epilayers grown on LiAlO2 and LiGaO2 substrate with two polar domains are investigated. LiAlO2 and LiGaO2 single crystal with a single domain structure and an adequate surface plane are promising substrates for the growth of high quality of hexagonal GaN thin films.

High performance 1.55 mu m InGaAsP/InP strained layer quantum well laser diodes fabricated by MOCVD overgrowth method

High performance uncooled 1.55 mu m InGaAsP/InP strained layer quantum well (SL-QW) lasers grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) were reported in this paper. Whole MOCVD over growth method were applied in this work. The threshold currents of 5mA and the highest lasing temperature of 122 degrees C were obtained.

Visible vertical cavity surface emitting laser

We have designed and fabricated the visible vertical-cavity surface-emitting lasers (VCSEL's) by using metalorganic vapor phase epitaxy (MOVPE). We use the 8 lambda optical cavities with 3 quantum wells in AlGaInP/AlGaAs red VCSEL's to reduce the drift leakage current and enhance the model gain in AlGaInP active region. The structure has a p-type stack with 36 DBR pairs on the top and an n-type with 55-1/2 pairs on the bottom. Using micro-area reflectance spectrum, we try to get a better concordance between the center wavelength of DBR and the emitting wavelength of the active region. We used a component graded layer of 0.05 lambda thick (x = 0.5 similar to 0.9) at the p-type DBR AlGaAs/AlAs interface to reduce the resistance of p-type DBR. We use selective oxidation to define the current injection path. Because the oxidation rate of a thick layer is faster than a thinner one, we grown a thick AlAs layer close to the active region. In this way, we got a smaller active region for efficient confinement of injected carriers (the aperture area is 3 x 3 mu m) to reduce the threshold and, at the same time, a bigger conductive area in the DBR layers to reduce the resistance. We employ Zn doping on the p-side of the junction to improve hole injection and control the Zn dopant diffusion to get proper p-i-n junction. At room temperature, pulse operation of the laser has been achieved with the low threshold current of 0.8mA; the wavelength is about 670nm.

The study of single mode 650nm AlGaInP quantum well laser diodes for DVD

Single mode 650nm AlGaInP quantum well laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) was reported in this paper. Selected buried rigewaveguid were applied for single mode operation especially for DVD use. The operating temperature over 90 degree at CW output power 5 mW was achieved.

Temperature dependence of photoluminescence of flat and undulated SiGe/Si multiple quantum wells

Photoluminescence (PL) of strained SiGe/Si multiple quantum wells (MQW) with flat and undulated SiGe well layers was studied at different temperature. With elevated temperature from 10K, the no-phonon (NP) peak of the SiGe layers in the flat sample has firstly a blue shift due to the dominant transition converting from bound excitons (BE) to free excitons (FE), and then has a red shift when the temperature is higher than 30K because of the narrowing of the band gap. In the undulated sample, however, monotonous blue shift was observed as the temperature was elevated from 10 K to 287 K. The thermally activated electrons, confined in Si due to type-II band alignment, leak into the SiGe crest regions, and the leakage is enhanced with the elevated temperature. It results in a blue shift of the SiGe luminescence spectra.

Type-II SiGe/Si MQWS (multi-quantum wells) and self-organized Ge/Si islands grown by UHV/CVD system

Type-II SiGe/Si MQWs (Multi-Quantum Wells) and Self-Organized Ge/Si Islands were successfully grown by a homemade ultra-high vacuum/chemical vapor deposition (UHV/CVD) system. Growth characteristics and PL (photoluminescence) spectra at different temperature were measured. It demonstrated that some accumulation of carriers in the islands results in the increase of the integrated PL intensity of island-related at a certain temperature range.

In situ annealing treatment and In-doping of GaN epilayers grown by MOVPE

The effects of in situ annealing treatment in the initial growth stage and In-doping during growth of the GaN on the material properties were investigated. GaN was grown by LP-MOVPE. In situ annealing reduced the full-width at half-maximum (FWHM) of X-ray rocking curves and reduced etch pit density of GaN films. It improved the optical properties of the epilayer. Undoped and In-doped GaN films of initial growth stage were investigated. It was found that morphology and optical properties were improved in In-doped samples. (C) 2000 Elsevier Science B.V. All rights reserved.

AlGaInP visible quantum well lasers for information technology

650 nm-range AlGaInP multi-quantum well (MQW) laser diodes grown by low pressure metal organic chemical vapor deposition (LP-MOCVD) have been studied and the results are presented in this paper. Threshold current density of broad area contact laser diodes can be as low as 350 A/cm(2). Laser diodes with buried-ridge strip waveguide structures were made, threshold currents and differential efficiencies are (22-40) mA and (0.2-0.7) mW/mA, respectively. Typical output power for the laser diodes is 5 mW, maximum output power of 15 mW has been obtained. Their operation temperature can be up to 90 degrees C under power of 5 mW. After operating under 90 degrees C and 5 mW for 72 hrs, the average increments for the threshold currents of the lasers at 25 degrees C and the operation currents at 5 mW (at 25 degrees C) are (2-3) mA and (3-5) mA, respectively. Reliability tests showed that no obvious degradation was observed after 1400 hours of CW operation under 50 degrees C and 2.5 mW.

Growth and characterization of GaN on LiGaO2

The nearly lattice-matched (0 0 1)LiGaO2 substrates have been used for the growth of GaN by LP-MOVPE, GaN epilayers have been grown on both domains at very low input partial pressure of hydrogen and relatively low growth temperature. The differences in the growth rate, crystal and optical qualities of hexagonal GaN epilayers grown on LiGaO2 substrate with two polar domains are investigated. LiGaO2 single crystal with a single domain structure and an adequate surface plane is a promising substrate for the growth of high quality of hexagonal GaN thin films. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

固氮树木丛枝菌根真菌(AMF)遗传多样性的研究

丛枝菌根是自然生态系统中分布最广的内生菌根，在促进植物生存与生长、植被恢复以及生物多样性保护等方面有着非常重要的作用。 随着现代分子生物学技术的不断发展，丛枝菌根真菌研究得到空前发展。大量DNA分析新技术在丛枝菌根真菌的分子遗传、分类鉴定、种间及种内亲缘关系、菌株持久性等方面得到应用，与传统菌根研究方法相比，表现出巨大的优越性。 本项研究利用分子生物学技术和研究方法对中国吉林长白山地区非豆科固氮植物以及东北地区固氮树木的丛枝菌根真菌DNA分子多态性及其与宿主植物之间的相互关系等进行初步研究，旨在利用分子生态学理论和研究方法揭示丛枝菌根真菌多样性及其与宿主植物之间相互适应和协同进化的一般规律，为更好地保护和利用这一重要的微生物资源提供理论依据。 通过比较与筛选，建立起丛枝菌根真菌痕量DNA快速、简便、高效的提取纯化方法——改良CTAB法。经PCR检测，所得DNA满足进一步研究的要求。 根据丛枝菌根真菌18s rRNA 小亚基核基因片段的特点，利用“科”特异性引物进行半巢式标记PCR (Labelled Primers-PCR，LP-PCR) 及单链构象多态性（Single-Stranded Conformation Polymorphism，SSCP）分析技术研究了长白山赤杨在属水平上表现出的多样性。另外，利用巢式PCR-RFLP技术，分别对来源于长白山不同海拔的四种赤杨菌根样品的AMF侵染情况及其系统进化进行了研究。利用AMF特异性PCR技术对我国东北地区四种非豆科树木和5种豆科树木菌根侵染情况和系统发育规律进行了研究 研究结果显示：赤杨根内AMF存在丰富的基因多样性。AMF的侵染有从宿主混乱性向宿主专一性发展的趋势。 长白山地区赤杨属植物至少有东北赤杨、西伯利亚赤杨和色赤杨三个树种在其“属”的水平上与共生的球囊霉科（Glomaceae）至少一个“种” 的丛枝菌根真菌，即根内球囊霉（Glomus intraradix），在“种”的水平上表现出不相关于宿主海拔高度的某种相互选择性。 东北赤杨AMF菌的宿主专一性水平最强，球囊霉属已成为东北赤杨的优势侵染类群；对于其余三种赤杨，AMF则出现宿主混乱现象。宿主因素比海拔因素对AMF侵染特异性的影响更为重要。 豆科与非豆科样本的混乱性都比较强，在特定植物和AMF属之间无特异侵染规律，相对来说，非豆科树木比豆科树木对于AMF的选择性要更强一些，更倾向于和球囊霉属与无梗孢囊霉属的AMF构建共生体。

固氮树木丛枝菌根真菌（AMF）遗传多样性的研究

丛枝菌根是自然生态系统中分布最广的内生菌根，在促进植物生存与生长、植被恢复以及生物多样性保护等方面有着非常重要的作用。 随着现代分子生物学技术的不断发展，丛枝菌根真菌研究得到空前发展。大量DNA分析新技术在丛枝菌根真菌的分子遗传、分类鉴定、种间及种内亲缘关系、菌株持久性等方面得到应用，与传统菌根研究方法相比，表现出巨大的优越性。 本项研究利用分子生物学技术和研究方法对中国吉林长白山地区非豆科固氮植物以及东北地区固氮树木的丛枝菌根真菌DNA分子多态性及其与宿主植物之间的相互关系等进行初步研究，旨在利用分子生态学理论和研究方法揭示丛枝菌根真菌多样性及其与宿主植物之间相互适应和协同进化的一般规律，为更好地保护和利用这一重要的微生物资源提供理论依据。 通过比较与筛选，建立起丛枝菌根真菌痕量DNA快速、简便、高效的提取纯化方法——改良CTAB法。经PCR检测，所得DNA满足进一步研究的要求。 根据丛枝菌根真菌18s rRNA 小亚基核基因片段的特点，利用“科”特异性引物进行半巢式标记PCR (Labelled Primers-PCR，LP-PCR) 及单链构象多态性（Single-Stranded Conformation Polymorphism，SSCP）分析技术研究了长白山赤杨在属水平上表现出的多样性。另外，利用巢式PCR-RFLP技术，分别对来源于长白山不同海拔的四种赤杨菌根样品的AMF侵染情况及其系统进化进行了研究。利用AMF特异性PCR技术对我国东北地区四种非豆科树木和5种豆科树木菌根侵染情况和系统发育规律进行了研究 研究结果显示：赤杨根内AMF存在丰富的基因多样性。AMF的侵染有从宿主混乱性向宿主专一性发展的趋势。 长白山地区赤杨属植物至少有东北赤杨、西伯利亚赤杨和色赤杨三个树种在其“属”的水平上与共生的球囊霉科（Glomaceae）至少一个“种” 的丛枝菌根真菌，即根内球囊霉（Glomus intraradix），在“种”的水平上表现出不相关于宿主海拔高度的某种相互选择性。 东北赤杨AMF菌的宿主专一性水平最强，球囊霉属已成为东北赤杨的优势侵染类群；对于其余三种赤杨，AMF则出现宿主混乱现象。宿主因素比海拔因素对AMF侵染特异性的影响更为重要。 豆科与非豆科样本的混乱性都比较强，在特定植物和AMF属之间无特异侵染规律，相对来说，非豆科树木比豆科树木对于AMF的选择性要更强一些，更倾向于和球囊霉属与无梗孢囊霉属的AMF构建共生体.

杉木人工林土壤有机碳动态及其稳定性研究

土壤有机碳的动态和稳定性是陆地生态系统碳循环和全球气候变化研究中的关键问题。人工林土壤有机碳受到气候条件、植被组成、植物生长发育过程以及人类干扰等多种因素的影响，其动态变化过程和稳定机制具有一定的特殊性。本研究以亚热带典型杉木人工林生态系统为研究对象，通过活性有机碳分析、酸水解和密度分组等方法将土壤有机碳分为周转速率不同的碳库，考查杉木人工林各土壤碳库在不同时间尺度上的动态变化，并通过分析找出杉木人工林土壤有机碳损失的主要途径和恢复的可能性。为准确评价杉木人工林土壤碳库的稳定性和可持续经营提供科学依据。通过系统的研究，得出以下结论： (1) 溶解性土壤有机碳和微生物生物量碳（MBC）含量具有明显的季节差异。土壤水溶性有机碳以夏季最高，杉木人工林最低值出现在秋季，常绿阔叶林和火力楠纯林则出现在冬季。土壤MBC均在秋季最高，冬季和夏季较低。从春季到秋季，土壤热水浸提有机碳（HWC）和碳水化合物（HWcC）含量持续降低；转入冬季以后，HWcC含量继续降低，而HWC含量只有常绿阔叶林继续降低，两种人工林略有升高。因此，土壤活性有机碳的季节变化规律受到植被类型的影响。 (2) 总体而言，杉木人工林从幼林阶段至成熟林阶段是一个土壤有机碳积累的过程。在杉木人工林发育的初期，土壤微生物数量、活性及其对底物的利用效率均较低，各碳库的含量呈减少的趋势，但土壤有机碳自身的顽固性增强；随着杉木人工林发育成熟，土壤微生物数量、活性及其对底物的利用效率均明显增加，土壤有机碳自身的顽固性减弱，各碳库含量则有所增加或趋于稳定。但与幼林阶段相比，成熟阶段土壤有机碳自身的顽固性增强，物理保护程度减弱。 (3) 在杉木纯林取代常绿阔叶林及其连栽过程中，土壤总有机碳含量逐渐降低，二代与三代纯林之间趋于平稳；活性碳库I (LP I)、顽固性碳、各密度组分有机碳含量、土壤微生物量、活性及其对底物的利用效率明显降低，生态系统不断退化。常绿阔叶林土壤有机碳顽固性指数显著高于杉木纯林。随着杉木连栽代数的增加，土壤有机碳顽固性并没有明显的变化，但受到的物理保护作用逐渐增强。而且土壤中非纤维素碳水化合物含量逐渐减少，而纤维素及其占总碳水化合物的比例逐渐增加，即生物有效性降低。 (4) 杉木人工林随着连栽代数的增加，土壤C贮量下降的数量和幅度均降低，表明其土壤有机碳库趋于稳定。 (5) 杉阔混交和杉阔轮栽模式均可显著增加土壤活性有机碳的含量和比重，提高土壤微生物对底物的利用效率，促使生态系统趋向成熟和稳定，有利于土壤生态功能的恢复和杉木人工林的可持续经营。 (6) 在不同植被类型和人为干扰条件下，热水浸提有机碳占总有机碳的比例（HWC/SOC）是表征土壤生物活性有机碳库周转的较好指标，可以用来指示土壤生物活性有机碳库的动态变化。纤维素占总碳水化合物的比例（LP II/ (LP I + LP II)）能够一定程度上反映人为干扰对土壤有机碳质量的影响，可以作为森林土壤有机碳生化质量的指标。碳库管理指数（CMI）可以反映森林生态系统土壤微生物对底物的利用效率，而碳库指数（CPI）则与活性有机碳的周转速率密切相关。

长白山赤杨从枝菌根真菌DNA分子多态性的研究

丛枝菌根是自然生态系统中分布最广的内生菌根，在促进植物生存与生长、植被恢复以及生物多样性保护等方面有着非常重要的作用。随着现代分子生物学技术的发展，丛枝菌根真菌的研究得到空前发展。大量DNA分析新技术在丛枝菌根真菌的分子遗传、分类鉴定、种间及种内亲缘关系、菌株持久性等方面得到应用，与传统菌根研究方法相比，表现出巨大的优越性。但相比国际而言，国内针对菌根真菌分子水平上的研究发展较为缓慢。本项研究对中国吉林长白山东北赤杨、西伯利亚赤杨、色赤杨丛枝菌根真菌DNA分子多态性进行初步研究，试图揭示其一般规律，为更好地利用这一资源提供理论依据。通过比较与筛选，得到丛枝菌根真菌痕量DNA快速、简便的提取纯化方法—改良CTAB法。经PCR检测，所得DNA满足进一步研究的要求。根据丛枝菌根真菌185 rRNA小亚基核基因片段的特点，利用“科”特异性引物进行半巢式标记PCR（Labelled Primers-PCR，LP-PCR）扩增，再经单链构象多态性（Single-Stranded Conformation Polymorphism，SSCP）分析来检测其DNA分子在“种”水平上表现出的多态性。研究结果显示：丛枝菌根真菌在“种”的水平上并未随各宿主的变化表现出丰富的多样性；长白山地区赤杨属植物至少有东北赤杨、西伯利亚赤杨和色赤杨三个树种在自身“属”的水平上与共生的球囊霉科（Glomaceae）至少一个“种”的丛枝菌根真菌，即根内球囊霉（Glomus intradix），在“种”的水平上表现出不相关于宿主海拔高度的某种相互选择性。