利用理论化学描述符预测多氯联苯的贝类净化

利用理论化学描述符和偏最小二乘法（PLS）对多氯联苯（PCBs）在贝类perna viridis和dreissena polymorpha体内的净化速率常数（kd）分别进行模拟分析,获得两个定量结构-活性相关模型（QSAR）.模型的交叉验证相关系数（Q2cum）分别为0.501,0.756,标准偏差为别为0.084,0.076,模型具有较高的预测能力和可靠性.模型中具有重要意义的参数包括平均分子极化率（α）,分子体积（MV）,分子质量（MW）,分子表面积（S）及总能（TE）.这些参数表明范德华力在贝类净化PCBs的过程中起到关键作用,PCBs在贝类体内的净化机制可能为PCBs在生物相和水相间的分配作用.     

基于双电荷层结构的CMOS单光子雪崩二极管

基于180nm标准CMOS工艺,设计了一种能够有效提高光子探测效率的双电荷层结构的单光子雪崩二极管.该器件结构采用P电荷层和逆行掺杂的深N阱形成PN结,选取不同的P电荷层掺杂浓度,对击穿电压进行优化,当P电荷层浓度为1×1018cm-3时,击穿电压为17.8V,电场强度为5.26×105 V/cm.进一步研究发现N电荷层的位置会影响漂移电流密度和扩散电流密度.当在深N阱与N隔离层交界处掺杂形成N电荷层,即N电荷层掺杂峰值距离器件表面为2.5μm时,器件性能最优.通过Silvaco TCAD仿真分析得到:在过偏压1V下,波长500nm处的探测效率峰值为62%,同时在300～700nm范围内的光子探测效率均大于30%.     

Dark count in single-photon avalanche diodes:A novel statistical behavioral model

Dark count is one of the inherent noise types in single-photon diodes,which may restrict the performances of detectors based on these diodes.To formulate better designs for peripheral circuits of such diodes,an accurate statistical behavioral model of dark current must be established.Research has shown that there are four main mechanisms that contribute to the dark count in single-photon avalanche diodes.However,in the existing dark count models only three models have been considered,thus leading to inaccuracies in these models.To resolve these shortcomings,the dark current caused by carrier diffusion in the neutral region is deduced by multiplying the carrier detection probability with the carrier particle current at the boundary of the depletion layer.Thus,a comprehensive dark current model is constructed by adding the dark current caused by carrier diffusion to the dark current caused by the other three mechanisms.To the best of our knowledge,this is the first dark count simulation model into which incorporated simultaneously are the thermal generation,trap-assisted tunneling,band-to-band tunneling mechanisms,and carrier diffusion in neutral regions to evaluate dark count behavior.The comparison between the measured data and the simulation results from the models shows that the proposed model is more accurate than other existing models,and the maximum of accuracy increases up to 31.48%when excess bias voltage equals 3.5 V and temperature is 50℃.