Selective electrodeposition of indium microstructures on silicon and their conversion into InAs and InSb semiconductors

Abstract: The idea of benefitting from the properties of III-V semiconductors and silicon on the same substrate has been occupying the minds of scientists for several years. Although the principle of III-V integration on a silicon-based platform is simple, it is often challenging to perform due to demanding requirements for sample preparation rising from a mismatch in physical properties between those semiconductor groups (e.g. different lattice constants and thermal expansion coefficients), high cost of device-grade materials formation and their post-processing. In this paper, we demonstrate the deposition of group-III metal and III-V semiconductors in microfabricated template structures on silicon as a strategy for heterogeneous device integration on Si. The metal (indium) is selectively electrodeposited in a 2-electrode galvanostatic configuration with the working electrode (WE) located in each template, resulting in well-defined In structures of high purity. The semiconductors InAs and InSb are obtained by vapour phase diffusion of the corresponding group-V element (As, Sb) into the liquified In confined in the template. We discuss in detail the morphological and structural characterization of the synthesized In, InAs and InSb crystals as well as chemical analysis through scanning electron microscopy (SEM), scanning transmission electron microscopy (TEM/STEM), and energy-dispersive X-ray spectroscopy (EDX). The proposed integration path combines the advantage of the mature top-down lithography technology to define device geometries and employs economic electrodeposition (ED) and vapour phase processes to directly integrate difficult-to-process materials on a silicon platform. Graphical abstract: [Figure not available: see fulltext.]

Electrochemically deposited nanocrystalline InSb thin films and their electrical properties

We present an electrochemical route to prepare nanocrystalline InSb thin films that can be transferred to an industrial scale. The morphology, composition, and crystallinity of the prepared uniform and compact thin films with a surface area of around 1 cm2 were investigated. The essential electrical characteristics such as conductivity, Seebeck coefficient, the type, concentration and mobility of charge carriers have been examined and compared with InSb nanowires obtained in the same system for electrochemical deposition (fixed pulse sequence, temperature, electrolyte composition, and system geometry). Moreover, obtained thin films show much higher band gap energy (0.53 eV) compared to the bulk material (0.17 eV) and InSb nanowires (0.195 eV)

Template assisted synthesis of highly ordered semiconducting nanowire arrays for thermoelectric application

Z punktu widzenia inżynierii materiałowej, rozwój nauki i technologii zmierza w kierunku zmniejszania wymiarów, po to aby otrzymywać struktury z coraz większą precyzją i o lepszej wydajności pracy. Powszechne zainteresowanie nanostrukturalnymi materiałami wynika głównie z faktu, że ich właściwości: optyczne, elektryczne i mechaniczne, zazwyczaj różnią się od tych obserwowanych dla materiałów o takim samym składzie chemicznym czy fazowym ale w większej skali. Wiele obiecujących strategii zostały już zaproponowanych do wytwarzania nanomateriałów. Wśród nich jest anodyzacja, z powodzeniem stosowana do produkcji nanoporowatych warstwy tlenku na powierzchni różnych metali. Po odpowiednim przygotowaniu, templaty z anodyzowanego glinu (AAO) mogą służyć jako szablony przeznaczone do produkcji wielu różnych nanomateriałów, takich jak: nanodruty, nanorurki i nanokropki. Syntezy oparta na matrycach jest jednym z najprostszych i tanich sposób wytwarzania nanostruktur. Celem przedstawionych w niniejszej pracy badań jest zoptymalizowanie metody otrzymywania nanostruktur, które mogą wykazywać znacznie lepsze właściwości elektryczne/termoelektryczne niż obecnie używane materiały. Kolejnym zadaniem postawionym przed autorem niniejszej rozprawy było zbadanie właściwości fizycznych uzyskanych nanostruktur i określenia możliwości ich praktycznego zastosowania. Przeprowadzono badania nad syntezą pięciu materiałów półprzewodnikowych lub kompozytowych. Na drodze elektrochemicznego osadzania przygotowano polikrystaliczne nanodruty oraz cienkie filmy z antymonku indu, dwuskładnikowe nanodruty i nanorurki kobaltowo-antymonowe, nanodruty kompozytowe polimerowo-metaliczne oraz nanodruty o złożonej strukturze z otoczka tlenkową i rdzeniem w postaci łańcucha nanocząstek. Dla wszystkich przygotowanych materiałów przeprowadzono badania nad ich morfologią, składem, krystalicznością. Dodatkowo przeprowadzono badania właściwości elektrycznych/termoelektrycznych nanostruktur InSb. Dla nanodrutów uzyskanych na drodze jednostopniowej elektropolimeryzacji połączonej z osadzaniem metalu zaproponowano mechanizm reakcji.From a material viewpoint, the advancement of science and technology provides the smaller and smaller dimensions with higher precision and enhanced performance. The widespread interest in nanostructured materials is mainly due to the fact that their properties, such as: optical, electrical, and mechanical are usually different from those of the bulk materials. Many promising strategies have been already reported for fabrication of nanomaterials. Among them, anodization has been successfully employed to fabricate nanoporous oxide layers on the surface of different metals. After suitable preparation, anodic aluminum oxide (AAO) membranes can serve as templates for fabrication of great variety of nanomaterials such as: nanowires, nanotubes and nanodots which offers a lot of modern technological applications. The goal of the research was to design the electrochemical methods for obtaining semiconducting or composite nanostructures which might exhibit significantly better electric/thermoelectric properties than currently used materials. The another task was to investigate the properties of synthesized materials and determine the possibility of their future applications. Optimization of synthesis of five materials in the form of nanostructures were carried out. Polycrystalline indium antimonide in form of nanowires and thin films, binary cobalt-antimony nanowires and nanotubes, composite polymeric-metallic nanowires and nanopeapods structures were prepared by electrodeposition. Morphology, composition, crystallinity, spectroscopic and electrical properties of the obtained nanostructures were characterized. Seebeck constant measurements were carried out for single InSb nanowires and thin films. For electropolymerization occurring simultaneously with deposition of metal, reaction mechanism was proposed

Distributed Bragg reflector based on porous anodic alumina fabricated by pulse anodization

In this paper, we demonstrate a distributed Bragg reflector (DBR) based on nanoporous anodic aluminum oxide (AAO) formed by pulse anodization. The AAO structure with alternating mild anodized (MA) and hard anodized (HA) layers having different porosities and thereby different refractive indices was fabricated in 0.3 M H 2 SO 4 using potential pulses of 25 and 35 V. The effective refractive index of the HA layers can be tailored by changing the porosity of the HA layers. The porosity of the HA layers can be significantly increased by selective chemical etching of HA segments in 0.52 M H 3 PO 4 . Before etching, the porous AAO structure was supported by a polymer nanorod frame. On the selected surface area pores were infiltrated with polymers (polystyrene and PMMA). The designed AAO structure consists of alternating high and low refractive index layers and behaves as a distributed Bragg mirror reflecting light in two different ranges of wavelength. This behavior is extremely important in optical communication lines where two separate spectral bands of high reflectivity in the infrared region are desired

pH sensors based on polypyrrole nanowire arrays

The hydroquinone monosulfonate-doped polypyrrole (PPy-HQS) nanowires were successfully fabricated by potentiostatic electropolymerization of pyrrole (Py) inside the pores of home-made through-hole anodic aluminum oxide (AAO) membranes. The AAO templates with a nominal pore diameter of 80 nm were prepared by a two-step anodization process. The potentiostatic electropolymerization of HQS-doped polymer nanowires was carried out in 0.1 M NaClO4, or 0.1 M LiClO4 or 0.1 M citric acid containing 0.05 M pyrrole and 0.05 M potassium hydroquinone monosulfonate. The synthesized PPy-HQS nanowire arrays were tested as potential potentiometric pH sensors. It was found that pH sensors based on PPy-HQS nanowires exhibited better electrochemical performance toward pH sensing than those based on PPy-HQS thin films. The best potentiometric response to pH changes and a very good stability in time showed the sensor based on the PPy-HQS nanowires polymerized in a 0.1 M LiClO4 solution

Electrochemical method of preparing metallic, polymeric and organic-inorganic hybrid nanowires inside porous anodic alumina templates

The fabrication of free standing silver, polypyrrole (PPy) and hybrid PPy – Ag nanowire arrays was reported. Silver, P Py and PPy – Ag nanowires were produced by electrochemical deposition/polymerization of metal/polymer in anodic aluminum oxide (AAO) templates. The home – made AAO templates were fabricated by two – step anodization of aluminum performed in oxalic acid, sulfuric acid and phosphoric acid at the anodizing potentials of 25 V, 45 V and 195 V, respectively. Silver nanowires with a diameter of ~40, 80 and 300 nm were synthesized by DC electrode position from a commercially available plating bath. PPy nanowires, ~80 nm in diameter, were synthesized by electropolymerization of a monomer in a solution containing pyrrole (Py) and NaClO 4 by applying a constant potential. The hybrid PPy – Ag nanowires, ~80 nm in diameter, were synthesized by a simple simultaneous cathodic elect ropolymerization of pyrrole and metal deposition in a solution containing HNO 3 , NaNO 3 , pyrrole (Py) and AgNO 3 by applying a constant potential. After the electrochemical deposition, free standing Ag, PPy and PPy – Ag nanowire arrays were obtained by a subseq uent chemical etching of the AAO template in an aqueous NaOH solution. The morphology and structural characterization of fabricated nanowires were performed by FE – SEM and EDAX analyses

Template-assisted electrodeposition of indium–antimony nanowires : comparison of electrochemical methods

Indium antimonide (InSb) is a III–V compound semiconductor that in a form of nanowires can possess improved thermoelectrical and optical properties compared to the corresponding bulk crystal. Here, we applied three electrodeposition techniques for a fast and inexpensive template-assisted fabrication of InSb nanowires from a sodium citrate-citric acid solution at room temperature. The home-made anodic aluminum oxide (AAO) templates with the pore diameter of 100 nm were used. InSb nanowires were synthesized by potentiostatic, galvanostatic and periodic pulse reverse techniques. The morphology, composition and crystallinity of as-obtained and annealed nanowires were investigated and compared with the literature data. It was found that the potentiostatic and pulse reverse methods gave crystalline nanowires. On the other hand, the constant current density deposition results in a partially amorphous nanowire material