Band Fillling 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 6 K 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 (σ = 21 meV). Spatially resolved CL wavelength mappings give a standard deviation of σ = 7 meV for the InGaN peak position across an area of 55 × 36 μm2. In time-resolved CL a strong monotonous redshift (ΔE = —60 meV) of the main emission line is observed during 4.5 μs decay following the function Epeak = E0 — 25 meV log (t/t0) which is attributed to a thermalization of carriers within a statistically distribution of localized states. This is supported by a blueshift (ΔE = 75 meV) of the emission line upon increasing cw excitation power by three orders of magnitude (Epeak = E0 + 25 meV log (P/P0).