Fabrication of silicon nanowires by electroless etching and investigation of their photovoltaic applications

Özdemir, Barış
Silicon is the most important semiconducting material for optoelectronics owing to its suitable and tunable physical properties. Even though there are several alternatives, silicon based solar cells are still the most widely produced and commercially feasible system. Extensive efforts have been spent in order to increase the efficiency and decrease the cost of these systems. The studies that do not focus on replacement of the semiconducting material, mostly concentrate on the developments that could be brought by nanotechnological approaches. In this aspect, utilization of silicon nanowires has been predicted to improve the efficiency of the silicon based solar cell technology. Moreover, besides solar cells, silicon nanowires have been investigated for many other electronic systems such as thermoelectrics, light emitting diodes, biological/chemical sensors, photodetectors and lithium ion v batteries. Therefore, production of silicon nanowires through a cost-effective and well controlled method could make important contributions to many fields. In this thesis, electroless etching method, which is a novel and solution based method enabling vertically aligned silicon nanowire array fabrication over large areas, is investigated. A detailed parametric study resulting in a full control over the resultant nanowire morphology is provided. The parameters affecting the structure have been determined as etching time, solution temperature, solution concentration, pressure and starting wafer characteristics. The results show that electroless etching method could replace the conventional silicon nanowire fabrication methods. It was shown that specific nanowire lengths for any application, can be obtained simply by adjusting the parameters of electroless etching system. One of the most crucial features of vertically aligned silicon nanowire arrays is their remarkable antireflective properties. The optical reflectivity measurements showed that 42% reflectivity of pristine polished silicon wafer decreases down to 1% following fabrication of silicon nanowire arrays on their surface. This unique characteristic reveals that these nanowires could be used as antireflective surfaces in solar cells. Moreover, it was determined that p-n heterojunctions that are formed by silicon nanowires, namely radial heterojunctions, would yield higher efficiencies compared to planar heterojunctions because of the dramatic increase in the charge carrier collection efficiency and orthogonal photon absorption. On this subject, n-type silicon nanowire arrays were fabricated by electroless etching followed by drop casting Poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) (PEDOT:PSS) organic layer on these nanowires as the complementary layer, forming the radial heterojunction. The energy conversion efficiency of silicon nanowire / PEDOT: PSS device was found as 5.30%, while planar silicon / PEDOT: PSS control device displayed only 0.62% efficiency. Developments and optimizations in both the electroless etching method and solar cell models could lead to important developments in photovoltaic industry.


Fabrication of SiO2-stacked diamond membranes and their characteristics for microelectromechanical applications
Bayram, Barış (Elsevier BV, 2011-04-01)
Diamond is a promising microelectromechanical systems (MEMS) material due to its high Young's Modulus and very large thermal conductivity. In this work, ultrananocrystalline diamond was stacked between silicon dioxide to form thermally-stable and robust membranes. These SiO2-stacked diamond layers were processed into MEMS-compatible membranes. For comparison, membranes composed of only SiO2 were fabricated as well. The structural characteristics of these membranes are compared and analyzed for membranes of ...
A study on the production and properties of in-situ titanium diboride particulate reinforced aluminum A356 alloy composite
Serdarlı, Osman; Sevinç, Naci; Kalkanlı, Ali; Department of Metallurgical and Materials Engineering (2011)
TiB2 particle reinforced aluminum matrix composites have been the subject of several investigations. An M.Sc. thesis on production of TiB2 reinforced aluminum composites by reaction between liquid aluminum and B2O3 and TiO2 dissolved in cryolite has been completed in this Department in 2005. This study is a continuation of the mentioned M.Sc.study. Composition of the starting cryolite-B2O3-TiO2 system, temperature and time were used as experimental variables. The resulting composite was squeeze cast and its...
Production of epoxide functionalized boehmite nanoparticles and their use in epoxide nanocomposites
Coniku, Anisa; Gündüz, Güngör; Maviş, Bora; Department of Chemical Engineering (2012)
In the present study the effects of addition of organically functionalized boehmite nano-particles on the mechanical properties of epoxy polymers were analyzed. Nanosize platelets of boehmite powders were produced via a hydrothermal process from the raw material aluminum trihydroxide Al(OH)3 provided by a a chemical supplier, but which in future studies can be replaced by local resources of aluminum trihydroxide available in Seydişehir, Turkey. The ground aluminum trihydroxide particles were submitted to a ...
Production and characterization of aluminum matrix composites for small-scale unmanned aircraft engine pistons
Demiralp, Muammer; Kalkanlı, Ali; Department of Metallurgical and Materials Engineering (2020)
The composite materials are used in every stage in life, from the aerospace industry to agriculture. In most composites, the primary purpose of adding reinforcement to the matrix material is to increase the strength and stiffness of the matrix. Nowadays, most engineering materials are replaced with the composite materials due to higher specific strength. In this study, particle reinforced metal matrix composite is used to produce pistons for a small-scale unmanned aircraft engine. Conventional pistons are p...
Atomic-layer-deposited zinc oxide as tunable uncooled infrared microbolometer material
Battal, Enes; Bolat, Sami; TANRIKULU, MAHMUD YUSUF; OKYAY, Ali Kemal; Akın, Tayfun (2014-11-01)
ZnO is an attractive material for both electrical and optical applications due to its wide bandgap of 3.37eV and tunable electrical properties. Here, we investigate the application potential of atomic-layer-deposited ZnO in uncooled microbolometers. The temperature coefficient of resistance is observed to be as high as -10.4%K-1 near room temperature with the ZnO thin film grown at 120 degrees C. Spectral noise characteristics of thin films grown at various temperatures are also investigated and show that t...
Citation Formats
B. Özdemir, “Fabrication of silicon nanowires by electroless etching and investigation of their photovoltaic applications,” M.S. - Master of Science, Middle East Technical University, 2011.