第四纪处于气候的快速波动期,黄土记录了丰富的古气候信息。为探讨汉江上游地区晚更新世以来气候变化过程,对汉江上游洋县境内汉江Ⅰ级河流阶地朱家村剖面沉积特征、常量元素分布、地球化学参数及形成时代进行研究。结果表明:汉江上游...第四纪处于气候的快速波动期,黄土记录了丰富的古气候信息。为探讨汉江上游地区晚更新世以来气候变化过程,对汉江上游洋县境内汉江Ⅰ级河流阶地朱家村剖面沉积特征、常量元素分布、地球化学参数及形成时代进行研究。结果表明:汉江上游Ⅰ级河流阶地形成于50 ka BP前后;剖面由下到上具有典型黄土(L_(1))→古土壤(S_(0))→全新世黄土(L_(0))→表层土(TS)的地层序列;剖面主要化学成分为SiO_(2)、Al_(2)O_(3)和Fe_(2)O_(3),化学风化过程中Ca、Na元素迁移淋失程度较高,K、Mg元素迁移淋失程度相对较低;剖面化学风化程度呈现从典型黄土(L_(1))→古土壤(S_(0))逐渐增强,到全新世黄土(L_(0))层又略降低的规律,记录了该区域气候在50~11 ka BP干燥寒冷,由11.00 ka BP开始逐渐增温增湿,2.50 ka BP到达最暖湿,2.50~0 ka BP持续降温变干的演变过程。研究成果可为我国北亚热带古气候重建提供数据参考。展开更多
Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieve...Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieved,significantly limiting the photoelectric performance of UV VCSELs.We developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs.In this study,by improving hole in-jection efficiency,the hole concentration in the HIL is increased,and the hole barrier at the electron barrier layer(EBL)/HIL interface is decreased.This minimises the hindering effect of hole injection.A mathematic-al model of this structure was established using a commercial software,photonic integrated circuit simulator in three-dimension(PICS3D).We conducted simulations and theoretical analyses of the band structure and carrier concentration.Introducing polarisation doping through the Al composition gradient in the HIL en-hanced the hole concentration,thereby improving the hole injection efficiency.Furthermore,modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface,smoothing the valence band.This improved the stimulated radiative recombination rate in the MQW,increasing the laser power.There-fore,the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.展开更多
文摘第四纪处于气候的快速波动期,黄土记录了丰富的古气候信息。为探讨汉江上游地区晚更新世以来气候变化过程,对汉江上游洋县境内汉江Ⅰ级河流阶地朱家村剖面沉积特征、常量元素分布、地球化学参数及形成时代进行研究。结果表明:汉江上游Ⅰ级河流阶地形成于50 ka BP前后;剖面由下到上具有典型黄土(L_(1))→古土壤(S_(0))→全新世黄土(L_(0))→表层土(TS)的地层序列;剖面主要化学成分为SiO_(2)、Al_(2)O_(3)和Fe_(2)O_(3),化学风化过程中Ca、Na元素迁移淋失程度较高,K、Mg元素迁移淋失程度相对较低;剖面化学风化程度呈现从典型黄土(L_(1))→古土壤(S_(0))逐渐增强,到全新世黄土(L_(0))层又略降低的规律,记录了该区域气候在50~11 ka BP干燥寒冷,由11.00 ka BP开始逐渐增温增湿,2.50 ka BP到达最暖湿,2.50~0 ka BP持续降温变干的演变过程。研究成果可为我国北亚热带古气候重建提供数据参考。
文摘Owing to the low p-type doping efficiency in the hole injection layers(HILs)of GaN-based ultra-violet(UV)vertical-cavity surface-emitting laser(VCSEL),effective hole injection in multi-quantum wells(MQW)is not achieved,significantly limiting the photoelectric performance of UV VCSELs.We developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs.In this study,by improving hole in-jection efficiency,the hole concentration in the HIL is increased,and the hole barrier at the electron barrier layer(EBL)/HIL interface is decreased.This minimises the hindering effect of hole injection.A mathematic-al model of this structure was established using a commercial software,photonic integrated circuit simulator in three-dimension(PICS3D).We conducted simulations and theoretical analyses of the band structure and carrier concentration.Introducing polarisation doping through the Al composition gradient in the HIL en-hanced the hole concentration,thereby improving the hole injection efficiency.Furthermore,modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface,smoothing the valence band.This improved the stimulated radiative recombination rate in the MQW,increasing the laser power.There-fore,the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.
