The thesis studies a three-dimensional rectangular hexahedron meshing (3D RHM) single-cell model to explore the cell behaviors for electronic cell-substrate impedance sensing (ECIS). In the model, a spatial network of resistors (R) and capacitors (C) is established to mimic a single-cell measurement system including electrodes, medium and mammalian cells. Unlike the existing ECIS models, which are limited by several approximations for current flow, spreading resistance and cell morphology, the proposed single-cell model is more flexible and enables us to provide high mesh resolution to reconstruct the real circumstances of cell and their surroundings. Moreover, the simulated results by single-cell model match the published measurement and simulation data by Thein and Huang. In addition, it is also demonstrated that the maximum change of total impedance (Z) between 100 Hz to 10 MHz varies based upon changes in cell properties, specifically the size of cell, cell membrane capacitance, cell-electrode distance, and cytoplasm resistivity, which is essential to understand the frequency-dependent cell behaviors.

Bottom-up semiconductor nanowires and their arrays have been frequently highlighted as building blocks for next-generation optoelectronic devices. Compared with planar thin films, vertical nanowires have unique properties, namely three-dimensional (3-D) geometries with high surface-to-volume ratios, small junction area, and heteroepitaxy. These capabilities lead to the designs of high-performance, integrated, and compact device platforms. Intrinsically, there is no fundamental difference in the semiconductor device physics or material characteristics between nanowires and traditional planar thin films. However, the relationship between the 3-D nanowire geometries and the material properties introduces unique aspects of carrier dynamics. Studying these dynamics is critical to exploring the rich electrical properties underlying the material characterizations and guiding the design of nanowire optoelectronic devices.

In this dissertation, we provide new insight into nanowire optoelectronics at infrared by investigating nanowire modeling, epitaxy, and devices. Since carrier dynamics in nanowires are much more complicated than those in thin films, we combine optical and electrical simulations to develop a more powerful scheme of 3-D modeling, allowing us to comprehensively interpret and understand the temporal and spatial motion of carriers in nanowires. Equipped with this simulation capability, we are able to propose novel device structures for infrared photodetection with better performance than their planar device counterparts. With these new insight as well as nanowire designs obtained from modeling, we then tackle the heteroepitaxy of nanowires on lattice mismatched substrates by selective-area metal-organic chemical vapor deposition and demonstrate the growth capability of high-quality materials within the 2 – 5 μm wavelength spectrum. Finally, we demonstrate an uncooled nanowire-based device platform for photodetection at short-wavelength infrared and mid-wavelength infrared. These three points of focus in this dissertation–modeling, epitaxy, and devices–are closely intertwined, and together provide a holistic picture of 3-D nanowire performance. We believe the presented theoretical and experimental work will stimulate more validating studies of nanowire optoelectronics at infrared to further reveal the inherent carrier dynamics of nanowires and develop more sophisticated nanowire optoelectronic devices.