Date of Award

Fall 12-15-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Nikolaus Dietz

Second Advisor

Vadym Apalkov

Third Advisor

Michael Williams

Fourth Advisor

Yohannes Abate

Abstract

The objective of this dissertation is to understand the structural and optoelectronic properties of group III-nitride materials grown by High-Pressure Metal Organic Chemical Vapor Deposition (HP-MOCVD) and Migration Enhanced Plasma Assisted MOCVD by FTIR reflectance spectroscopy, Raman spectroscopy, X-ray diffraction, and Atomic Force Microscopy.

The influence of the substrates/templates (Sapphire, AlN, Ga-polar GaN, N-polar GaN, n-GaN, and p-GaN) on the free carrier concentration, carrier mobility, short-range crystalline ordering, and surface morphology of the InN layers grown on HP-MOCVD were investigated using those techniques. The lowest carrier concentration of 7.1×1018 cm-3 with mobility of 660 cm2V-1s-1 was found in the InN film on AlN template, by FTIR reflectance spectra analysis. Furthermore, in addition to the bulk layer, an intermediate InN layers with different optoelectronic properties were identified in these samples. The best local crystalline order was observed in the InN/AlN/Sapphire by the Raman E2 high analysis. The smoothest InN surface was observed on the InN film on p-GaN template.

The influence of reactor pressures (2.5–18.5 bar) on the long-range crystalline order, in plane structural quality, local crystalline order, free carrier concentration, and carrier mobility of the InN epilayers deposited on GaN/sapphire by HP-MOCVD has also been studied using those methods. Within the studied process parameter space, the best material properties were achieved at a reactor pressure of 12.5 bar and a group-V/III ratio of 2500 with a free carrier concentration of 1.5x1018 cm-3, a mobility in the bulk InN layer of 270 cm2 V-1s-1 and the Raman (E2 high) FWHM of 10.3 cm-1. The crystalline properties, probed by XRD 2θ–ω scans have shown an improvement with the increasing reactor pressure.

The effect of an AlN buffer layer on the free carrier concentration, carrier mobility, local crystalline order, and surface morphology of InN layers grown by Migration-Enhanced Plasma Assisted MOCVD were also investigated. Here, the AlN nucleation layer was varied to assess the physical properties of the InN layers. This study was focused on optimization of the AlN nucleation layer (e.g. temporal precursor exposure, nitrogen plasma exposure, and plasma power) and its effect on the InN layer properties.

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