Semester

Fall

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Lawrence A Hornak

Committee Co-Chair

Jeremy Dawson

Committee Member

Dimitris Korakakis

Abstract

In recent years Light Emitting Diodes (LEDs) of high efficiency and long lifetime have been produced. Gallium Nitride in particular is used in the manufacture of Blue LEDs because it is a direct band gap semiconductor which can be alloyed with AlN and InN allowing band gap energies to range from 1.9eV to 6.2eV, which allows the emission of short wavelengths including blue light. The interest in replacing conventional lighting by solid-state lighting has led to focus on the development of high brightness Gallium Nitride (GaN) LEDs. Efficient LED structures such as flip chip configurations and Resonant Cavity LEDs (RCLEDs) typically need a highly reflective ohmic contact on p-GaN. RCLEDs are of great interest due their features such as, high spectral purity, and high emission intensity when compared to conventional GaN based LEDs [1]. Au based contacts are not appropriate for the RCLEDs due to low reflectance in the blue region. Ag films have much higher reflectivity in the visible region when compared to Au films.;The first part of the thesis presents the detailed fabrication process and characterization of Ag based electrodes for III-Nitride Resonant Cavity LEDs. A GaN/AlGaN Distributed Bragg reflector (DBR) of very high reflectance is employed on the sapphire substrate below the LED, which acts as the bottom mirror. For the top mirror, low resistance and highly reflective ohmic contacts on p-type GaN were achieved using an Ag-based metallization scheme. The second part of the thesis presents, development of a transparent, conductive zinc oxide contact to a GaN/InGaN MQW LED. A process and post-deposition annealing have been optimized to obtain ZnO films with high electrical conductivity and transparency, and ZnO-based contacts with a low contact resistance. This work represents a step toward the fabrication of high-efficiency GaN-based blue and green LEDs with transparent ZnO electrodes.

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