Semester

Summer

Date of Graduation

2011

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Lane Department of Computer Science and Electrical Engineering

Committee Chair

Dimitris Korakakis

Abstract

III-Nitride based semiconductors have emerged as one of the promising materials for electronic and opto-electronic devices, including but not limited to, solid state emitters, photodetectors, and transistors. Despite commercial success, several issues ranging from material growth to device fabrication remain unresolved and continue to hinder the efficiency of these devices. One such issue includes strain management in III-Nitride heterostructures. The binary alloys in the (Al,In,Ga)N family are characterized by a large lattice and thermal mismatch which leads to defect formation and cracking within heterostructures. These defects are detrimental to device fabrication and operation. This work investigates growth based techniques to manage strain in III-Nitride heterostructures and thereby reduce defect formation.;In particular, this work focuses on the development surfactant assisted growth and digital alloys as strain relieving techniques to minimize cracking in Aluminum Gallium Nitride (AlxGa1- xN) alloys and related heterostructures via Metal Organic Vapor Phase Epitaxy. Indium has been investigated as a surfactant in the growth of AlN/GaN Distributed Bragg Reflectors (DBRs) and has been shown to reduce the cracking by a factor of two. Using variable temperature x-ray diffraction studies, indium has been shown to influence the thermal expansion coefficients of the AlN layers. The digital growth technique has been investigated as a viable method for achieving high quality, crack free AlxGa 1-xN films. Alloys with an AlN mole fraction ranging from 0.1 to 0.9 have been grown by adjusting the periodicity of these short period superlattice structures. High resolution x-ray diffraction has been used to determine the superlattice period along with the a- and c-lattice parameter of the structure. High aluminum content digital AlxGa1-xN alloys have been employed in DBRs for high reflectivity, >94%, crack-free structures. The characterization of these structures via scanning electron microscopy, atomic force microscopy, and x-ray diffraction is presented along with the results from the integration of the DBR with visible wavelength LEDs.

Download

Share

COinS