高质量InGaN的等离子体辅助分子束外延生长和In的反常并入行为

采用射频等离子体辅助分子束外延技术生长得到了In组分精确可控且高质量的In_xGa_1-xN (x ≤ 0.2) 外延薄膜. 生长温度为580 ℃的In_0.19Ga_0.81N薄膜(10.2) 面非对称衍射峰的半高宽只有587弧秒, 背景电子浓度为3.96× 10¹⁸/cm³. 在富金属生长区域, Ga束流超过N的等效束流时, In组分不为零, 即Ga并没有全部并入外延层; 另外, 稍微增加In束流会降低InGaN的晶体质量. 关键词： InGaN 外延薄膜 射频等离子体辅助分子束外延 In 并入 晶体质量     

计入衍射几何因子和多重性因子的立方GaN相含量的测定

以回摆法衍射峰的积分强度为基础,提出了X射线衍射分析单晶体时的多重性因子和衍射几何因子的概念,推导出普遍适用的相含量计算公式.利用双晶X射线多功能四圆衍射仪测绘GaN/GaAs(001)外延层中立方相（002）面、{111}面和六角相{100}面的极图和倒易空间Mapping,分析了六角相和立方相微孪晶的各晶面在极图中的分布特征及计算相含量时的多重性因子和衍射几何因子,并根据立方相(002)、立方相微孪晶{111}、六角相{101}和{100}衍射峰的积分强度,求得外延层中立方相微孪晶和六角相的含量.     

立方相GaN外延层的表面起伏和高密度孪晶与六角相

利用扫描电子显微镜(SEM)、原子力显微镜(AFM)、透射电子显微镜(TEM)和X射线衍射(XRD)技术研究了低压金属有机化学气相淀积(LP-MOCVD)的立方相GaN/GaAs(001)外延层的表面起伏特征,及其与外延层极性和内部六角相、立方相微孪晶之间的联系.结果表明外延表面存在有大量沿方向延伸的条带状台阶,而表面起伏处对应着高密度的六角相或立方相微孪晶,在表面平整的区域内其密度则较低.{111}_Ga和{111}_N面上形成六角相和微孪晶概率的明显差异是导致外延层表面台阶状起伏特征的根本原因.     

Si(001)衬底上APCVD生长3C-SiC薄膜的微孪晶及含量

利用X射线双晶多功能四圆衍射仪,对在Si(001)衬底上使用常压化学气相方法(APCVD)生长的3C-SiC进行了微孪晶的分析.Φ扫描证明了3C-SiC外延生长于Si衬底上,生长的取向关系为：(001)_3C-SiC//(001)_Si,［111］_3C-SiC//［111］_Si.3C-SiC的{111}极图在χ=15.8°出现了新的衍射,采用六角相{10^{1010}晶面的极图以及孪晶SiC(002)的倒易空间Mapping分析了χ=15.8°处产生的衍射为3C-SiC的孪晶所致,并利用ω扫描估算了孪晶的含量约为1%.     

Recent progress of colloidal quantum dot based solar cells

Colloidal quantum dot(CQD) solar cells have attracted great interest due to their low cost and superior photo-electric properties. Remarkable improvements in cell performances of both quantum dot sensitized solar cells(QDSCs) and PbX(X = S, Se) based CQD solar cells have been achieved in recent years, and the power conversion efficiencies(PCEs) exceeding 12% were reported so far. In this review, we will focus on the recent progress in CQD solar cells. We firstly summarize the advance of CQD sensitizer materials and the strategies for enhancing carrier collection efficiency in QDSCs, including developing multi-component alloyed CQDs and core-shell structured CQDs, as well as various methods to suppress interfacial carrier recombination. Then, we discuss the device architecture development of PbX CQD based solar cells and surface/interface passivation methods to increase light absorption and carrier extraction efficiencies. Finally, a short summary, challenge, and perspective are given.     

GaNAs基超晶格太阳电池的分子束外延生长与器件特性

采用分子束外延(MBE)生长技术生长了周期厚度不同的1 e V吸收带边的Ga N0.03As0.97/In0.09Ga0.91As应变补偿短周期超晶格(SPSL)。高分辨率X射线衍射(HRXRD)测量结果显示,当周期厚度从6 nm增加到20 nm时,超晶格的结晶质量明显改善。然而,当周期厚度继续增加时,超晶格品质劣化。对超晶格周期良好的样品通过退火优化,获得了具有低温光致发光现象的高含N量Ga NAs/In Ga As超晶格,吸收带边位于1 e V附近。使用10个周期的Ga NAs/In Ga As超晶格(10 nm/10 nm)和Ga As组成的p-i-n太阳电池的短路电流达到10.23 m A/cm2。经聚光测试获得的饱和电流密度、二极管理想因子与由电池暗态电流-电压曲线得到的结果一致。     

GaN横向外延中晶面倾斜的形成机制

采用双晶X射线衍射(DC-XRD)研究蓝宝石(0001)衬底上横向外延GaN层中晶面倾斜的形成原因. 发现横向生长区的GaN在垂直掩模方向上朝SiN_x掩模层弯曲. 采用选择性腐蚀逐渐去掉SiN_x掩模层, 发现XRD中GaN(0002)w扫描衍射峰两侧存在与晶面倾斜有关的衍射信息. 该衍射信息起初为一个很宽的峰, 随着选择性腐蚀的进行, 会先分裂为两个峰, 最后当SiN_x掩模层全部腐蚀掉后, 其中一个衍射峰会消失, 而只剩下一个很窄的峰. 作者证实造成横向外延GaN 中晶面倾斜的原因有两个: 一是由于GaN与掩模层之间界面应力造成的弹性非均匀应变; 另一个是由于GaN中穿透位错的90°转向造成的塑性形变.     

1 eV吸收带边GaInAs/GaNAs超晶格太阳能电池的阱层设计

使用In, N分离的GaInAs/GaNAs超晶格作为有源区是实现高质量1eV带隙 GaInNAs基太阳能电池的重要方案之一. 为在实验上生长出高质量相应吸收带边的超晶格结构, 本文采用计算超晶格电子态常用的Kronig-Penney模型比较了不同阱层材料选择下, 吸收带边为1 eV的GaInAs/GaNAs超晶格相关参数的对应关系以及超晶格应变状态. 结果表明: GaNAs与GaInAs作为超晶格阱层材料在实现1 eV的吸收带边时具有不同的考虑和要求; 在固定1 eV的吸收带边时, GaNAs材料作为阱层可获得较好的超晶格应变补偿, 将有利于生长高质量且充分吸收的太阳能电池有源区. 关键词： GaInAs/GaNAs超晶格 Kronig-Penney模型 太阳能电池     

Crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth

The crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth (ELO) on sapphire (0001) substrates was investigated by using double crystal X-ray diffraction (DC-XRD). It was found that ELO GaN stripes bent towards the SiN_x mask in the direction perpendicular to seeding lines. Each side of GaN (0002) peak in DC-XRD rocking curves was a broad peak related with the crystallographic tilt. This broad peak split into two peaks (denoted as A and B), and peak B disappeared gradually when the mask began to be removed by selective etching. Only narrow peak A remained when the SiN_x mask was removed completely. A model based on these results has been developed to show that there are two factors responsible for the crystallographic tilt: One is the non-uniformity elastic deformation caused by the interphase force between the ELO GaN layer and the SiN_x mask. The other is the plastic deformation, which is attributed to the change of the threading dislocations (TDs)—from vertical in the window regions to the lateral in the regions over the mask.