Regensburg 2007 – scientific programme

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DS: Fachverband Dünne Schichten

DS 18: Symposium: In situ Optics I

DS 18.4: Invited Talk

Wednesday, March 28, 2007, 16:30–17:00, H34

In-situ monitoring of stress evolution in growing group-III-nitride layers — •Alois Krost, Armin Dadgar, Rainer Clos, Gunther Straßburger, and Fabian Schulze — Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg

Strains and stresses in heteroepitaxy are omnipresent but until recently, due to a lack of in-situ access, the potential problems were often not observed at the source: Stress can lead to misfit dislocations or cracking of layers as well as strongly curved wafers after epitaxy, which has to be avoided for high quality devices. An in-situ sensor monitoring stress is not only useful for monitoring strain during the growth of highly mismatched systems as Group-III-Nitrides, which are usually grown on heterosubstrates, but also for strain balanced Quantum-Wells or Bragg mirrors. It is a very useful tool, especially in difficult to control systems as GaN-on-Si, where tensile thermal strain leads to cracking for layers even below 1 µm in thickness. Therefore to apply strain engineering methods and optimize growth an in-situ stress sensor is prerequisite. We will show how stress can be determined during epitaxy and that not only film stress but also the composition of ternary alloys can be determined exactly. We will discuss the limits of Stoney’s equation, usually applied to calculate film stress, and present an analytical method for the determination of wafer curvature and elastic stress also in the non-linear range.