Ghanashyam Krishna Mamidipudi

Bio: Ghanashyam Krishna Mamidipudi is an academic researcher. The author has contributed to research in topics: Materials science & Visible spectrum. The author has an hindex of 1, co-authored 1 publications receiving 13 citations.

Metal Induced Crystallization

Abstract: Polycrystalline silicon thin films have attracted the attention of semiconductor industries in the past few decades due to their wide applications in thin film transistors, solar cells, display units and sensors (Schropp & Zeman, 1998; Choi et al., 2005; Mahan et al., 2008). Polycrystalline Si thin films are generally fabricated by crystallizing amorphous Si (a-Si) thin films, because these can render larger grains compared to the conventional poly Si film deposition. As a consequence, a variety of methods for lowering the crystallization temperature of a-Si have been developed. Excimer laser annealing is one of the promising ways to achieve large grain size poly Si films at lower substrate temperatures. Its high costs and nonuniform grain size, however, are significant obstacles that prevent its wide use (Parr et al., 2002). The other promising technique is the solid phase crystallization method. But this technique is essentially a high-temperature process and many substrates, including most forms of glass, cannot withstand the thermal processing. In order to achieve lower costs and have a wider range of application, inexpensive materials such as glass and special polymers have to substitute quartz or PyrexTM substrates. In the case of glass substrates, all of the processing steps need to be limited to temperatures below 550 °C. The other known technique is rapid thermal annealing (RTA). In RTA infrared radiation is used as a heating source, and has the advantage of the high heating speed (up to 60 oC/s) that reduces the crystallization time. In RTA radiation is applied in pulses to heat the sample without heating the glass substrate (which is transparent to the infrared radiation). However, the grain size obtained in the crystallization of a-Si is also in the range of a few micrometers.

Highly Reactive Crystalline (001) Facet of BiI3 Hexagonal Nanoplates for Visible Light Photodetectors

Abstract: A simple and facile solution phase synthesis of large-scale, micro-to-nanometer sized bismuth triiodide (BiI3) single crystalline hexagonal plates is reported. It is demonstrated that under optimized conditions the reactions result in dominant exposed (001) facets. Because of the large size, high surface-to-volume ratio, and thickness, BiI3 nanoplatelets are attractive as visible light photodetectors. At 1 V bias, the photoresponsivity is 0.87 A W–1; the specific detectivity is 4.8 × 1012 jones with a response rise time of 1 s and a fall time of 0.97 s. The Kelvin probe force microscope images revealed that the surface potential difference across the junction was 42.5 mV, which is attributed to the work function difference between the sample and substrate. The results of this study indicate that single hexagonal platelets of BiI3 are very promising for visible light photodetector applications.

BiFeO3-Black TiO2 Composite as a Visible Light Active Photocatalyst for the Degradation of Methylene Blue

Abstract: The application of a novel BiFeO3 (BFO)-black TiO2 (BTO) composite (called BFOT) as a photocatalyst for the degradation of methylene blue is reported. The p–n heterojunction photocatalyst was synthesized for the first time through microwave-assisted co-precipitation synthesis to change the molar ratio of BTO in BiFeO3 to increase the photocatalytic efficiency of the BiFeO3 photocatalyst. The UV–visible properties of p–n heterostructures showed excellent absorption of visible light and reduced electron–hole recombination properties compared to the pure-phase BFO. Photocatalytic studies on BFOT10, BFOT20, and BFOT30 have shown that they decompose methylene blue (MB) in sunlight better than pure-phase BFO in 70 min. The BFOT30 photocatalyst was the most effective at reducing MB when exposed to visible light (97%). Magnetic studies have shown that BTO is diamagnetic, and the BFOT10 photocatalyst exhibits a very weak antiferromagnetic behavior, whereas BFOT20 and BFO30 show diamagnetic behavior. This study confirms that the catalyst has poor stability and weak magnetic recovery properties due to the non-magnetic phase BTO in the BFO.

Tin induced a-Si crystallization in thin films of Si-Sn alloys

Abstract: Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si1−xSnx, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si1−xSnx exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

Self-sustained cyclic tin induced crystallization of amorphous silicon

Abstract: Experimental evidences for a recently proposed mechanism of tin-induced crystallization of amorphous silicon are presented. The mechanism discusses a crystalline phase growth through cyclic processes of formation and decay of a super-saturated solution of silicon in molten tin at the interface with the amorphous silicon. The suggested mechanism is validated using a nonlinear dynamical model that takes into account the mass diffusion of the components of the system, heat transfer caused by latent (crystallization) heat release and amorphous silicon dissolution events, and concentration nonuniformities created by silicon crystallization. The analysis of a stationary-state solution of the model confirms the existence of periodic solutions for the partial volume of the crystalline phase and other system’s variables. Possible applications of the proposed mechanism in manufacturing of cost-effective nanocrystalline silicon films for the third-generation solar cell technology are discussed.

Nanocrystals Growth Control during Laser Annealing of Sn

Abstract: An efficient technique for low temperature metal-induced nanocrystalline silicon fabrication is presented. The technique is based on laser annealing of thin films of “amorphous silicon-tin” composites combined with in situ control and monitoring with Raman technique. Laser annealing was shown to provide the possibility of fine-tuning the nanocrystals size and concentration, which is important in photovoltaic and thermoelectric devices fabrication.

Influence of Laser Light on the Formation and Properties of Silicon Nanocrystals in a-Si/Sn Layered Structures

Abstract: The influence of the laser light intensity and the temperature on the tin-induced crystallization of amorphous silicon has been studied using the Raman screening and optical microscopy methods. The existence of non-thermal mechanisms giving rise to the influence of laser light on the formation of silicon nanocrystals and their Raman spectra is demonstrated experimentally. The photoionization of silicon and the electron-phonon interaction are considered as possible origins of the detected effects. The prospects of their application in new technologies for producing nano-silicon films used in solar cells are discussed.