Performance limitation of Si Nanowire solar cells: Effects of nanowire length and surface defects
Deepika Bora, Shrestha Bhattacharya, Nitin Kumar, Aishik Basu Mallick, Avriti Srivastava, Mrinal Dutta, Sanjay K. Srivastava, P. Prathap, C. M. S. Rauthan
In Si nanowire (SiNW) solar cells enhanced light confinement property in addition to decoupling of charge carrier collection and light absorption directions plays a significant role to resolve the draw backs of bulk Si solar cells. In this report we have studied the dependence of the phovoltaic properties of Si NW array solar cells on the SiNW length and enhanced surface defect states as a result of enhanced surface area of the NWs. The SiNW arrays have been fabricated using metal catalyzed electroless etching (MCEE) technique. p-n junction has been produced by spin-on-dopant technique followed by thermal diffusion process. Front and rear electrodes have been deposited by e-beam evaporation techniques. SiNW lengths have been controlled from ~ 320 nm to 6.4 micro meter by controlling the parameters of MCEE technique. Photovoltaic properties of the solar cells have been characterized by measuring quantum efficiency and photocurrent density vs. voltage characteristics. Morphological studies have been carried out by using scanning electron microscopy. Reduction in light trapping capability comes at the benefit of reduced surface defects. The reduction of surface defects has been proved to be more advantageous in comparison to the decrement of light trapping capability. The major contribution to the changes in cell efficiency comes from the enhancement of short circuit current density with a very weak dependence on open circuit voltage. This work is beneficial for the production commercial Si solar cell where SiNW arrays could be used as a antireflection coating instead of using separate antireflection layers and thus could reduced the production cost.
Drastic effect of sequential deposition resulting from flux directionality on the luminescence efficiency of nanowire shells
核-壳纳米线异质结构形成了许多创新器件的基础。当通过定向沉积技术生长复合纳米线壳时，生长反应器中不同组分的源的方位角位置、衬底旋转和纳米线自遮蔽不可避免地导致顺序沉积。在这里，我们发现，在$_{0.15}$ Ga $_{0.85}$ As/GaAs壳层量子阱的分子束外延生长的发光效率的这种顺序性的剧烈影响。采用与迁移增强外延相对应的助熔剂顺序生长的壳层量子阱的光致发光强度。e.当As和III族金属基本上不同时撞击时，比用基本上重叠的通量制备的壳量子阱高两个数量级以上。透射电子显微镜没有发现任何扩展缺陷解释这种差异。我们的光致发光瞬态分析表明，共沉积有两个不利的微观效应。首先，较高密度的电活性点缺陷导致内部电场降低电子-空穴波函数重叠。第二，更多的点缺陷形成，作为非辐射复合中心。我们的研究表明，源的生长反应器，这仅仅是平面结构的技术相关性的安排，可以有严重的后果纳米线壳的材料性能。我们希望这一发现也适用于其他合金纳米线壳。
High-Responsivity Photodetection by Self-Catalyzed Phase-Pure P-GaAs Nanowire
缺陷对于光电子器件是有害的，例如堆垛层错可以形成载流子传输势垒，并且具有深能级的外来杂质（Au）可以形成载流子陷阱和非辐射复合中心。本文首先研制了具有纯锌层（ZB）结构的自催化p型GaAs纳米线（NWs），并以此制作了光电探测器。由于不存在堆垛层错并抑制了大量深能级缺陷，该光电探测器在室温下具有1.45 x 105 A W^-1的高光响应度，对波长为632.8 nm的低强度光信号具有高达1.48 x 10^14琼斯的优异比探测率（D*），优于先前报道的NW基光电探测器。这些结果表明，这些自催化纯ZB GaAs纳米线是光电子应用的有前途的候选人。
