Abstract:
In this research, a detailed study of electronic and optical properties of InGaN/GaN nanowire array photodetectors employing numerical techniques has been demonstrated. Intersubband transition energies and corresponding optical absorption coefficients, regarding quantum well based active region of the nanowire, have been studied by adjusting quantum well width, barrier width, diameter and polarization fields in the nanowire heterostructure solving Poisson and Schrodinger equations self consistently both in one and two dimensions. Upon studying first principle DFT technique, density of states and optical absorption coefficients regarding InGaN quantum dot based active region have been elucidated considering multiple sets of exchange correlation functionals and pseudopotentials. Optical absorption coefficient peaks, regarding InGaN quantum dot consisting of height 30 Å, base 10 Å and number of atoms 288, has been observed around 1.8 µm and 1.6 µm wavelengths employing generalized gradient approximation (GGA) and meta generalized gradient approximation (MGGA) exchange correlation functionals respectively taking into account 20%, 34% and 45% indium incorporations. Upon investigating quantum confinement in the active region of InGaN/GaN nanowire array-based photodetectors, nature of propagation in such array guided system has been investigated employing finite element method (FEM). Reflectance, transmittance and absorbance of light in InGaN/GaN nanowire array-based waveguide have been determined as a function of wavelength for both with and without indium incorporation in the nanowire. Material inhomogeneity of the nanowire waveguide has been employed by considering complex refractive index of the constituent materials whereas structural inhomogeneity has been taken into account by randomly varying the diameter of the nanowire in three different sets of ranges namely 60 nm to 100 nm, 90 nm to 130 nm and 120 nm to 160 nm. Role of lateral surface potential associated with InGaN/GaN nanowire array based photodetectors have been studied under visible and near-infrared illumination by solving Poisson and continuity equations in a coupled manner in two dimensions. Based on the obtained results, photoconductive gain and photocurrent have been investigated to elucidate the role of 2-D effects on the performance of these InGaN/GaN nanowire array based photodetectors. This thesis in effect provides necessary guidelines to develop InGaN/GaN nanowire array based photodetectors which will facilitate the design of monolithic photonic integrated circuits to be utilized for next generation optoelectronics.
