Berlin 2008 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

DS: Fachverband Dünne Schichten

DS 8: Semiconductor Nanophotonics: Materials, Models, Devices - GaN based Photonics I: Polaritzation Fields

DS 8.2: Invited Talk

Monday, February 25, 2008, 14:45–15:15, H 2032

Polarization induced effects in GaN-based devices — •Oliver Ambacher — Fraunhofer Institute for Applied Solid State Physics, Tullastr. 72, D-79108 Freiburg, Germany

The macroscopic non-linear pyroelectric polarization of wurtzite AlGaN, InGaN and AlInN ternary compounds dramatically affects the optical and electrical properties of multilayered Al(In)GaN/GaN hetero-, nanostructures and devices, due to the huge built-in electrostatic fields and bound interface charges caused by gradients in polarization at surfaces and heterointerfaces. In the presentation we review the theoretical and experimental results of the elastic and pyroelectric properties of binary and ternary group-III-nitrides with wurtzite crystal structure. We develop an improved method to calculate the piezoelectric and spontaneous polarization taking non-linearities due to alloying and/or high internal strain into account. Polarization induced interface charges and sheet carrier concentrations of 2DEGs are predicted for pseudomorphic InGaN/GaN, AlGaN/GaN and AlInN/GaN quantum well and heterostructures on the basis of the improved theory and compared with experimental results achieved by a combination of elastic recoil detection, high resolution X-ray diffraction, X-ray standing wave, photoluminescence, C-V profiling, and Hall effect measurements. Based on the improved model of polarization induced surface and interface charges a review of novel sensors based on AlGaN/GaN-heterostructures is provided, enabling a detailed understanding of the detection mechanisms and new functionalities of these interesting devices.