Synthesis of Gallium Nitride by Laser-Assisted Metal Organic Vapor Phase Epitaxy

Authors

Matthew J. Mitchell, University of Nebraska- LincolnFollow

Date of this Version

5-2012

Document Type

Article

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Electrical Engineering, Under the Supervision of Professor Yongfeng Lu. Lincoln, NE: May, 2012

Copyright 2012 Matthew J. Mitchell

Abstract

For the past two decades, gallium nitride (GaN) has become one of the most studied materials in the fields of optics and electronics due to its unique properties.Currently available methods for the synthesis of GaN require a high substrate temperature of 1100 ^oC, which can lead to several issues including a high defect concentration and increased probability of cracking and warping of films due to differences in thermal expansion coefficients between the substrate and film. The high growth temperature also prevents the integration of GaN devices with CMOS fabrication techniques, which has a post-process temperature limit of ~575 oC. Accordingly, there is a need for a low-temperature synthesis technique such as laser-assisted metal organic vapor phase epitaxy(L-MOVPE) to combat these issues. By using a carbon dioxide (CO₂) laser as the energy source for MOVPE, localized heating can be achieved, which lowers the overall substratetemperature.Over the course of this project, an L-MOVPE system was designed and built, and experiments were carried out to synthesize various morphologies of GaN nanostructure sat low substrate temperatures. The results show the L-MOVPE is capable of producing GaN nanowires with lengths up to 2 μm, and widths around 2 nm. Crystal structures were grown in all sizes ranging from 40 nm to 40 μm, all of which displayed prominentA1(LO) and E2H peaks, indicating high quality GaN. The largest crystal was found to have a growth rate of ~ 500 to 600 μm/hour, which is significantly higher than growth rates associated with conventional methods. In addition to films and nanowires, other nanostructures including nano-pillars, nano-flowers, and patterned GaN crystals were also grown, all at substrate temperatures ranging from 550 to 850 o C. These results are significant, because they show that through L- MOVPE, it is possible to achieve low-temperature growth of GaN. The low-temperature method allows GaN synthesis to be efficiently paired with current CMOS techniques, significantly increasing its potential applications in electronics.