Compressive

1. AlGaN:Si SiH4 AlGaN Tensile _ g m=6.5 GPa/mm 1120 250 nm Compressive Stress gradient in AlGaN:Si induced by dislocation bendingJoan M. Redwing, Penn State University, DMR 0606451 The incorporation of Si dopants in GaN and AlGaN thin films has previously been shown to increase tensile strain in the films and reduce the critical thickness for film cracking. We have used in-situ wafer curvature techniques to study the effect of Si doping on the stress and microstructure of AlxGa1-xN (x0.39–0.45) films grown by metalorganic chemical vapor deposition on SiC substrates. The measurements revealed a compressive-to-tensile transition of the stress state at the film surface upon the addition of SiH4 during growth, which correlated with a change in the angle of inclination of threading dislocations (TDs) in the film. The experimentally measured stress gradient (6.5 GPa/mm) was in good agreement with the value of 8.8±3.2 GPa/mm predicted by the dislocation effective climb model, indicating that dislocation inclination is the dominant mechanism responsible for tensile stress generation in the films. Weak-beam dark-field TEM image of AlGaN film showing change in angle of TDs at point of SiH4 addition. Experimentally measured change in incremental stress in Si-doped AlGaN as a function of film thickness.

2. Outreach to Middle School/High School StudentsJoan M. Redwing, Penn State University, DMR 0606451 The PI participated in a mentoring program for middle school girls. The program is designed to stimulate interest in science and technology via the development of personal relationships with women faculty at Penn State. Over the past year, three activities were held including two hands-on workshops on smart sensors and nanofabrication and a field trip to the Franklin Institute Museum in Philadelphia. Partial financial support for this program was provided by the NSF through this grant, a NIRT grant and the Penn State MRSEC. Graduate students supported by this grant participated in an engineering open house event for visiting high school students and presented a series of hands-on demonstrations illustrating the applications of compound semiconductors in lighting and illumination. PI and mentor program participants at the Franklin Institute Museum in Philadelphia Graduate student Ian Manning demonstrating applications of light emitting diodes in lighting