AVS 53rd International Symposium
    Thin Film Friday Sessions
       Session TF+EM-FrM

Invited Paper TF+EM-FrM6
In-Situ Studies of Stress Evolution during the Heteroepitaxial Growth of Group III-Nitrides

Friday, November 17, 2006, 9:40 am, Room 2022

Session: In-Situ/Ex-Situ & Real-Time Monitoring and Characterization
Presenter: J.M. Redwing, Penn State University
Authors: J.M. Redwing, Penn State University
S. Raghavan, Penn State University
X. Weng, Penn State University
J.D. Acord, Penn State University
E.C. Dickey, Penn State University
Correspondent: Click to Email
The group III-nitrides (GaN, AlN, InN and related alloys) are an important class of III-V semiconductors that form the basis for commercial high brightness blue/green light emitting diodes, laser diodes and high power microwave electronics for military and communication applications. Due to difficulties associated with the bulk crystal growth of GaN, group-III nitride thin films are grown heteroepitaxially on substrates such as sapphire, silicon carbide and silicon. These substrates have significantly different lattice constants and coefficients of thermal expansion than GaN, which can result in thin film stress, dislocation formation and film cracking. In addition to the epitaxial and thermal mismatch stresses, which are well known, growth-related stresses due to developing film morphology also play an important role, but are not as well understood for the GaN materials system. In this study, we have utilized in-situ wafer curvature measurements to study the magnitude and evolution of growth stress during the metalorganic chemical vapor deposition of group III-nitride thin films. Specific examples will be presented including the case of GaN growth on silicon and AlGaN growth on silicon carbide. By combining the in-situ measurements with post-growth atomic force microscopy and cross-sectional transmission electron microscopy, we correlate the growth stress to microstructural changes in the film arising from island coalescence and dislocation bending and demonstrate that dislocation density reduction in AlGaN films primarily occurs when the film is growing under a compressive stress. Methods to mitigate stress and reduce film cracking including the use of compositionally graded buffer layers will also be discussed.