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Growth of AlN crystals and AlGaN epitaxy on AlN wafers
North Carolina State University, MSE (NCSU), 1001 Capability Dr., Raleigh, NC 27695, United States
|For the first time in history of III-nitrides, the availability of low defect density (<103 cm-2) native AlN substrates offers an opportunity for growth of AlGaN alloys and device layers that exhibit million-fold lower defect densities than the incumbent technologies and enable one to assess and control optical end electrical properties in absence of extended defects. Epi-ready AlN wafers are fabricated from AlN boules grown by physical vapor transport at temperatures between 2200 and 2300°C. Gradual crystal expansion is achieved through a scalable, iterative re-growth process in which the high crystal quality is maintained over many generations of boules.
Despite the excellent crystal quality, below bandgap optical absorption bands in the blue/UV range affect the UV transparency of wafers. We use density functional theory (DFT) to develop a model to understand the interplay of point defects responsible for this absorption. We show a direct dependence of the mid-gap absorption band with the carbon concentration within the AlN.
Low defect density AlN and AlGaN epitaxial films are grown upon these wafers that exhibit superior optical properties in terms of emission efficiency and line width and can be doped with an efficiency that is several orders of magnitude higher than possible in technologies using non-native substrates. UV LED structures and laser diodes were fabricated on these materials that exhibit low turn-on voltages and record low lasing threshold.
This presentation will review state-of-the-art of AlN-based technology and give examples of potential applications in future devices and contrast these with other wide bandgap technologies.
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Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Zlatko Sitar
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-05-07 19:11 Revised: 2013-05-08 14:54