Band filling and energy relaxation in InGaN/GaN-multiple quantum well structures

An InGaN/GaN multiple quantum well structure grown by low pressure MOCVD on c-Al2O3 substrate is investigated using spectral-time-resolved cathodoluminescence microscopy (CL). At 6K the laterally integrated CL spectrum shows a very efficient blue emission from the InGaN multiple quantum well centered at 2.841 eV with an FWHM of 50 meV (sigma = 21 meV). Spatially resolved CL wavelength mappings give a standard deviation of sigma=7 meV for the InGaN peak position across an area of 55 x 36 mu m(2). In time-resolved CL a strong monotonous redshift (Delta E = -60 meV) of the main emission line is observed during 4.5 mu s decay following the function E-peak = E-0 - 25 meV log (t/t(0)) which is attributed to a thermalization of carriers within a statistically distribution of localized states. This is supported by a blueshift (Delta E = 75 meV) of the emission line upon increasing cw excitation power by three orders of magnitude (Epeak = E-0 + 25 meV log (P/P-0).