Sapphire Substrate Geometrical Effects on III-N Blue LED Material Properties
In this presentation, we will analyze a set of experiments designed to understand the effect of (0001) sapphire c-plane substrate physical dimensions (thickness, diameter, bow/warp/TTV, edge beveling) and crystal properties (misorientation, surface roughness) on uniformity and reproducibility of constituent LED layers. Our initial studies have found that precisely controlled crystal misorientation (offcut) towards the m-plane is a significant factor influencing wafer-to-wafer peak wavelength variation, GaN surface roughness, and p-doping levels. Quantitative analysis of these results with respect to variation in typical substrate manufacturing capabilities will be presented; the trends are in agreement with the materials characteristics explored in our previous studies [1, 2]. Warp and bow are critical parameters for control over GaN material characteristics. Furthermore, tight control over the total thickness variation (TTV) is needed to obtain highly uniform, repeatable sub-micron dimensions used to create current patterned substrate (PSS) wafers.
 D. Lu, D.I. Florescu, D.S. Lee, V. Merai, J.C. Ramer, A. Parekh, and E.A. Armour, “Sapphire substrate misorientation effects on GaN nucleation layer properties”, J. Crystal Growth 272:353, (2004).
 D. Lu, D.I. Florescu, D.S. Lee, V. Merai, A. Parekh, J.C. Ramer, S.P. Guo, and E. Armour, “Advanced characterization studies of sapphire substrate misorientation effects on GaN-based LED device development”, Phys. Stat. Sol.(a) 200:71, (2003).