Date of Award

8-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics

First Advisor

Devki Talwar, Ph.D.

Second Advisor

Muhammad Numan, Ph.D.

Third Advisor

Ajawad I. Haija, Ph.D.

Abstract

A great deal of interest has emerged in recent years to design novel compound semiconductor materials to fulfill the growing societal needs of efficient light sources, powerful solar cells, miniaturized-electronic-circuitry for lab-on-chip equipment, and a plethora of handheld opto-electronic devices. GaAs-based III-V compounds are significant materials with important fundamental characteristics allowing the scientists and engineers to envision their use in a variety of devices including light-emitting diodes (LEDs), laser diodes (LDs), and high-electron mobility transistors (HEMTs). In this regard, there has been a growing interest of studying the far-infrared optical properties in both un-doped and doped bulk III-V compounds, thin films, ternary alloys, and their nano-structured quantum-wells and superlattices. For GaAs/AlxGa1-xAs materials grown especially by molecular-beam epitaxy (MBE), the optical constants [viz., n, k, N (Charge carrier concentration), R (Reflection), and T (Transmission)] over a broad frequency regime are fundamental inputs that must be known for constructing opto-electronic devices. Despite some success by using Raman Spectroscopy, the influence of free charge carrier concentration on the phonon-plasmon coupled modes (L±) by far-infrared (FIR) spectroscopy are still scantily known. Any effort to extract accurate information about the charge carrier concentration N in either n- or p-type doped III-V compounds using FIR would be of significant importance to the scientific community. In this thesis, we will use the electromagnetic theory to study the IR reflectivity and transmission at oblique incidence in both undoped and doped GaAs, AlxGa1-xAs thin films and superlattices in order to correlate the shifts of the L± mode frequencies with the free charge carrier concentration. The transmission study in compound semiconductors for s-polarization reveals a single minimum at the resonance frequency of the TO mode, while for p-polarization the transmission minima occur at both the resonance frequencies of the TO and LO modes. In doped semiconductor thin films, the transmission in p-polarization exhibits minima at TO and L+ with a shift of L+ mode to higher frequency as the charge carrier concentration increases.

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