Berlin 2008 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 55: GaN: preparation and characterization II

HL 55.1: Vortrag

Freitag, 29. Februar 2008, 10:30–10:45, ER 164

Time dependent changes of the spontaneous polarization field in GaN investigated via UHV-cathodoluminescence and photoluminescence — •Martina Finke, Daniel Fuhrmann, Holger Jönnen, Uwe Rossow, and Andreas Hangleiter — TU Braunschweig, Inst. f. Angewandte Physik, 38106 Braunschweig

In GaN-based quantum well structures, the spontaneous and piezoelectric fields have a strong effect on the optical properties. The spontaneous field is normally screened by charged species on the surface. Since the spontaneous field counteracts the piezoelectrical field, a reduction of the quantum confined Stark effect (QCSE) indicated by a blueshift in the peak position of luminescence and an increased intensity is expected by descreening the spontaneous field. We use cathodoluminescence under well controlled surface conditions. This leads to metastable changes of the QW emission spectra as a function of irradiation dose, which was investigated via photo(PL)- and cathodoluminescence(CL) in an UHV environment. As samples we used various GaInN quantum well structures with or without AlGaN electron barrier and a variation in GaN cap thickness. The electron-beam produces electron-hole pairs in the sample, which can be separated by the spontaneous field. The holes created in the buffer layer reduce the spontaneous field, which can be observed as a redshift and decrease in intensity of emitted light. Simultaneous measurements of PL and CL allow us to study the screening and descreening of the spontaneous field due to electron-hole pairs at various electron-beam penetration depths.