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。

降雨作用下滑坡转化泥石流分析研究

对降雨入渗条件下诱发北川县魏家沟泥石流起动的影响因素进行研究。在室内人工降雨试验模拟泥石流起动的基础上,得到魏家沟泥石流起动的临界雨强,并利用FLAC软件建立降雨在坡体中入渗分析的数值模拟模型,分析坡度、雨强、土性参数以及土体饱和度对坡体失稳的影响,坡体在降雨情况下塑性区的出现与延展及坡面拉应力区的发展情况。研究结果表明:降雨入渗后孔隙水压力的升高主要在坡脚附近,即距坡脚1/5的坡高范围内。坡脚处孔隙水压力最大,沿着坡面往上逐渐减小,且坡面较大水平位移也主要集中在1/5坡高范围内。因此,降雨入渗诱发泥石流的起动最先可能出现在坡脚附近,并随着坡度增加、雨强增大、土体饱和度增大,坡体稳定性降低至失稳,促进泥石流的起动。