Growth and Fabrication of GaN and InxGa1-xN Based Optoelectronic Devices

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Title: Growth and Fabrication of GaN and InxGa1-xN Based Optoelectronic Devices
Author: Berkman, Erkan Acar
Advisors: Dr. Salah M. Bedair, Committee Co-Chair
Dr. Nadia A. El-Masry, Committee Chair
Dr. Mark Johnson, Committee Member
Dr. Jerry J. Cuomo, Committee Member
Abstract: In this study, heteroepitaxial growth of III-Nitrides was performed by metalorganic chemical vapor deposition (MOCVD) technique on (0001) Al2O3 substrates to develop GaN and InxGa1-xN based optoelectronic devices. Comprehensive experimental studies on emission and relaxation mechanisms of InxGa1-xN quantum wells (QWs) and InxGa1-xN single layers were performed. The grown films were characterized by x-ray diffraction (XRD), Hall Effect measurements, photoluminescence measurements (PL) and transmission electron microscopy (TEM). An investigation on the effect of number and width of QWs on PL emission properties of InxGa1-xN single QWs and multi-quantum wells (MQW) was conducted. The experimental results were explained by the developed theoretical bandgap model. The study on the single layer InxGa1-xN films within and beyond critical layer thickness (CLT) demonstrated that thick InxGa1-xN films display simultaneous presence of strained and (partially) relaxed layers. The In incorporation into the lattice was observed to be dependent on the strain state of the film. The findings on InxGa1-xN QWs and single layers were implemented in the development of InxGa1-xN based LEDs and photodiodes, respectively. The as-grown samples were fabricated using conventional lithography techniques into various optoelectronic devices including long wavelength LEDs, dichromatic monolithic white LEDs, and p-i-n photodiodes. Emission from InxGa1-xN⁄GaN MQW LEDs at wavelengths as long as 625nm was demonstrated. This is one of the longest peak emission wavelengths reported for MOCVD grown InxGa1-xN MQW structures. Dichromatic white emission in LEDs was realized by utilizing two InGaN MQW active regions emitting at complementary wavelengths. InGaN p-i-n photodiodes operating at various regions of the visible spectrum tailored by the i-layer properties were developed. This was achieved by the novel approach of employing InxGa1-xN in all layers of the p-i-n photodiodes, enabling nearly-lattice matched growth. The photodiodes displayed zero-bias responsivity values as high as 0.037A⁄W, and the peak responsivity wavelength of the photodiodes ranged between 416nm and 466nm. To the author's best knowledge, the latter value remains the longest peak detection wavelength among InxGa1-xN based p-i-n photodiodes.
Date: 2008-08-18
Degree: PhD
Discipline: Materials Science and Engineering

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