This proposal will be awarded using funds made available by the American Recovery and Reinvestment Act of 2009 (Public Law 111-5), and meets the requirements established in Section 2 of the White House Memorandum entitled, Ensuring Responsible Spending of Recovery Act Funds, dated March 20, 2009. I also affirm, as the cognizant Program Officer, that the proposal does not support projects described in Section 1604 of Division A of the Recovery Act.
The objectives of this research are to i) gain an understanding of and ii) create a predictive methodology for crack initiation and overall crystal quality evolution for Aluminum Nitride (AlN) single crystals during processing. AlN has outstanding electrical and thermal properties making it particularly well-suited for high power, high frequency, energy efficient electronic and photonic devices, such as light emitting diodes (LEDs) and laser diodes, but the use of AlN is currently limited by the high production cost. Crystal IS, the industrial partner on this proposal, has developed a new technology for growing large AlN crystals - up to 50 mm in diameter. However, these large crystals often crack due to stresses that arise when the material is cooled from its growth temperature as high as 2300C. In this project, a team of experts in the fields of stress measurement and simulation of loaded materials from Cornell and Rensselaer will study AlN as a "structural" material. High energy X-rays will be used to "see" the crystal structure of the AlN deep inside a test specimen as it is loaded. By matching simulations to the experimental results, key temperature-dependent mechanical properties, related to strength, stiffness and fracture resistance will be determined. This information will be used in a crystal growth process model to predict crystal quality for given growth conditions.
This work will guide crystal growth process designers so that large, high quality crystals can be produced. This work will be integrated into educational programs at the participating institutions. The industrial collaboration will provide excellent learning opportunities. Any experimental capabilities developed will reside at the x-ray beamline and become available to other users.
