The current paper reports the prospects of a multiple-graphene-layer (MGL) based vertically doped p ++ -n-n --n ++ avalanche photo-sensor in visible wavelength region (300 nm-800 nm). High carrier mobility, intrinsic optical and mechanical properties in graphene at room temperature, have made this material promising for various novel applications. The authors have used an indigenously developed and experimentally verified quantum-corrected field maximum classical drift-diffusion (QCFMCDD) mathematical model for studying the optical characteristics of MGL based p ++ -n-n --n ++ avalanche photo-diode sensor. The validity of the simulator is established through a comparative study between the experimental and analytical observations under similar operating (structural/electrical/thermal) conditions. Additionally, the superiority of the QCFMCDD model over the conventional classical drift-diffusion model is established through this comprehensive study. The analysis reveals that the opto-electrical properties of the device-under-test improve significantly as a result of the incorporation of MGL in the low doped active region. The authors have compared the results with those of a Si/4H-SiC super-lattice avalanche photo-sensor at 500 nm wavelength of incident radiation. It is observed that graphene outperforms its Si/4H-SiC counterpart in terms of photo-responsivity (0.820 A W −1 vs. 0.650 A W −1 ) and quantum efficiency (84% vs. 62%) for optical irradiation with visible laser source. The opto-electrical performance of the 3 × 3 array type graphene photo-sensor is further analyzed and compared with those of its single array counterpart. The photo-responsivity as well as quantum efficiency increases by at least 30% in the case of the 3 × 3 photo-sensor array. In comparison to available photo detectors, reported so far in published literature, the designed photo-sensor shows overall performance betterment in the visible wavelength region. To the best of authors' knowledge, this is the first report on MGL based 3 × 3 array type ultra fast highly sensitive visible avalanche diode photo-sensor.

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In the chapter, the authors describe how a plant can be selected as a natural indicator of heavy metal (mercury) contamination, how one can select a plant species to monitor a particular type of heavy metal and use those plants to remove the contaminants from the area under consideration. The chapter also contains a brief idea of environmental contamination by heavy metals and how the situation can be managed by the techniques of modern plant biotechnology. The authors add some reports and data of their in-vitro studies of mercury toxicity on Ananas sp., generally known as pineapple, for better understanding of the text.

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