Dresden 2006 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

HL: Halbleiterphysik

HL 50: Poster II

HL 50.20: Poster

Donnerstag, 30. März 2006, 16:30–19:00, P3

Optical and electrical properties of nitride-based UV LEDs — •D. Fuhrmann, T. Retzlaff, T. Litte, H. Bremers, U. Rossow, D. Dräger, and A. Hangleiter — TU Braunschweig, Inst. f. Angewandte Physik, Mendelssohnstr. 2, 38106 Braunschweig, Germany

During the last years, the efficiency of UV light emitting diodes based on AlGaN/AlGaN or GaN/AlGaN quantum well (QW) structures was strongly improved. But still, they are about one order of magnitude less efficient compared to their GaInN/GaN-based counterparts emitting in the visible spectrum. In this contribution we show our approach in order to optimize the internal quantum efficiency (IQE) of GaN/AlGaN QWs with an emission wavelength around 350nm. The samples were grown by low pressure MOVPE. The good material quality of the AlGaN buffer layer was revealed by both XRD measurements and the low temperature PL linewidth. We used temperature and excitation power dependent photoluminescence to determine the IQE. For our structures we find IQE values as high as 26% under resonant excitation. Using a nonresonant excitation with a power density of some kW/cm² the IQE increases even to 38%. For optimized SQW structures we find a very similar behavior concerning the IQE dependence on temperature and excitation power for both GaN/AlGaN UV-emitting structures and GaInN/GaN blue light emitters. This indicates that in both cases similar mechanisms limiting the IQE are present. A further improvement was achieved by applying an AlN buffer layer between the sapphire substrate and the AlGaN layer. Then we observed a significant improvement of the n- and p-type doping of the AlGaN layer, which will help to realize a high power UV-LED.