Regensburg 2013 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 68: Poster Session: GaN: devices & preparation & characterization; III-V semiconductors; Photonic crystals; Semiconductor lasers

HL 68.8: Poster

Mittwoch, 13. März 2013, 16:00–20:00, Poster A

Quantification of internal electric fields in InGaN/GaN quantum wells by differential phase contrast microscopy — •Matthias Lohr¹, Ralph Schregle¹, Ines Pietzonka², Martin Strassburg², Robert Leute³, Ferdinand Scholz³, Knut Müller⁴, Andreas Rosenauer⁴, and Josef Zweck¹ — ¹Fakultät für Physik, Universität Regensburg — ²Osram Opto Semiconductors, Regensburg — ³Institut für Optoelektronik, Universität Ulm — ⁴Institut für Festkörperphysik, Universität Bremen

LEDs and laser diodes play an important role in our daily lives. A very promising and intensively studied material system is GaN with InGaN quantum wells. It is capable to cover the whole visible spectral range by changing the In content. When trying to tune the output wavelength from blue to green light however, big problems in efficiency emerged. In the literature this became known as the "green gap". An important property of the non-centrosymmetric GaN crystal and possible cause of the efficiency droop is the internal piezoelectric field.

In this work direct and quantitative measurements of InGaN/GaN heterostructures combining STEM and differential phase contrast (DPC) method will be shown. The detected signal is related to the product of the piezoelectric field strength and the sample thickness. The calibration of the inelastic mean free path (IMFP) of electrons in GaN was determined by HAADF STEM and EELS. Using this data, the thickness became accessible. Based on the IMFP thickness maps in combination with calibrated DPC measurements, fields in the range from 10-100 MV/m have been measured in different samples.