Md Rezaul Karim – Seminar/Master Defense, Friday, March 17, 2017 at 11:00 A.M.

JSNN – Md Rezaul Karim – Master Thesis Defense/Friday Seminar

Candidate: Md Rezaul Karim

Advisor and Committee Chair: Shanthi Iyer, Ph.D.

Department: Nanoengineering

Date: Friday, March 17, 2017

Time: 11:00 A.M. – 1:00 P.M.

Location: JSNN Auditorium

2907 E. Gate City Blvd., Greensboro, NC 27401

Title: “Modeling of the Growth Rate, Electrical and Optical Properties of GaAsSb Nanowires.”

Abstract:

GaAsSb nanowires have attracted much attention due to its bandgap tunability over a wide range from 0.73 eV to 1.42 eV, the possibility of both type I and type II band alignments with GaAs, enhanced compositional homogeneity and improved structural and optical properties. For harnessing the full potential of semiconductor nanowires, insight to the growth mechanism in the form of analytical model is essential. Further, numerical simulation of experimental characteristics can be exploited for quantification of pertinent electrical and optical properties.

In this thesis, first a semi-empirical mass conservation of the growth-species-based-model has been proposed encompassing different material transport pathways. The secondary fluxes re-emitted from the surface of the side facets of the neighboring NWs contribute substantially towards the growth for smaller pitch lengths, while those from the oxide surface dominate at larger pitch lengths at higher V/III beam equivalent pressure ratios. Excellent agreement between the experimental and simulated results have been observed for the pitch dependent axial and radial NW dimensions of both the axial and core-shell configured GaAsSb NWs.

Second, pseudo- three dimensional (3-D) finite element method simulation has been applied for numerical modeling of current-voltage characteristics and photoluminescence spectra of GaAsSb nanowires. Electrical transport parameters, namely, mobility, carrier lifetime and carrier concentration have been extracted by best fit of the simulation to the experimental results.

Finally, 3-D finite difference time domain simulation technique has been utilized to perform electromagnetic simulations of GaAsSb nanowire arrays.  The optical absorptance has been estimated and optimum array design parameters (nanowire diameter and pitch length) in terms of integrated absorption were determined for GaAsSb axial and GaAs/GaAsSb core-shell nanowire arrays. Moreover, pitch length induced variation in photoluminescence peak intensity has been demonstrated to arise from the differences in absorptance of nanowire arrays with different pitch lengths.