All-optical switching application of germano-silicate optical fiber incorporated with Ag nanocrystals

银纳米晶体掺杂的高非线性石英光纤的全光转换应用

子午岭林区人工与天然油松林(Pinus tabulaeformis)养分库和碳库特征

为了揭示黄土高原地区人工油松林自然化发育过程中的植物叶片与土壤养分库和碳库的变化规律,采用典型样地法,以子午岭林区天然油松群落为参照,选择了不同立地条件的人工油松林,分别对其土壤的氮库、碳库及植物叶片养分库和碳库进行了分析。结果表明,该区油松针叶C、N、P的含量平均值分别为(499.5±63.75)mg/g、(8.53±0.50)mg/g和(0.94±0.64)mg/g,叶片C含量大小依次为阳坡天然林>阴坡天然林>阴坡人工林>阳坡人工林,阳坡人工林叶片N、P含量显著高于阳坡天然林。不同立地条件下油松林叶片C/N、C/P差异显著,叶片N、P和N/P均达到极显著水平,但是叶片C含量差异不显著。油松叶片C含量与N、P含量均呈极显著负相关,N和P之间的呈显著正相关。不同立地的油松林除40～60cm土层土壤C、N含量无显著差异外,0～20cm和20～40cm两个土层的人工林土壤C、N含量显著高于天然林,同时阳坡人工林土壤C、N含量显著高于阴坡人工林。0～20cm、20～40cm两个土层土壤C含量与N含量均呈极显著正相关,与植物N、P均呈显著正相关。子午岭林区阳坡的人工油松林不仅叶片养分含量较高,而且林地土壤是该区土壤的...

云雾山自然保护区优势植物种群分布格局的分形特征

对宁夏云雾山草原自然保护区植物种群分布格局的分形计盒维数进行了研究。结果表明:本氏针茅、铁杆蒿和百里香是该区的优势种。3种优势种的计盒维数在1.7左右,表明它们具有较大的空间占据能力。但是它们的计盒维数最大值出现的时间不同,本氏针茅、百里香计盒维数最大值出现在封育20a的样地中,铁杆蒿出现在封育25a的样地中。

A Multi-Finger Si_(1-x)Ge_x/Si Heterojunction Bipolar Transistor for Wireless Power Amplifier Applications

A large area multi-finger configuration power SiGe HBT device(with an emitter area of about 880μm~2)was fabricated with 2μm double-mesa technology.The maximum DC current gain β is 214.The BV_(CEO) is up to 10V,and the BV_(CBO) is up to 16V with a collector doping concentration of 1×10~(17)cm~(-3) and collector thickness of 400nm.The device exhibits a maximum oscillation frequency f_(max) of 19.3GHz and a cut-off frequency f_T of 18.0GHz at a DC bias point of I_C=30mA and V_(CE)=3V.MSG(maximum stable gain)is 24.5dB,and U(Mason unilateral gain)is 26.6dB at 1GHz.Due to the novel distribution layout,no notable current gain fall-off or thermal effects are observed in the I-V characteristics at high collector current.

Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

清洗后硅片表面的电子结构

介绍了一种含表面活性剂和螯合剂的新型半导体清洗剂和清洗工艺。利用红外吸收谱、X射线光电子谱和原子力显微镜等，把它和标准RCA清洗工艺的清洗效果做了比较。测试结果表明，经清洗过的硅片表面主要是由硅、氧和碳三种元素组成，它们分别以Si-O健、C-O健和Si-C键的形式存在。两种清洗技术都在硅片表面产生氧化硅层，在硅片表面都存在有机碳污染，但新型半导体清洗工艺产生的有机碳污染少于标准RCA清洗。在对硅片表面的粗糙化影响方面，新型半导体清洗技术清洗明显优于标准RCA清洗技术。