Stimulated emission and optical gain in nitride-based compounds and quantum structures

On the basis of investigation of photoluminescence (PL) dynamics of highly excited structures with different In content under strong excitation by short laser pulses and comparison with model calculations we analyze emission mechanisms in these In-containing systems. The obtained PL spectra in various In-containing samples exhibit stimulated emission line on the short-wavelength side of the spontaneous PL band. We suggest theoretical model for optical transitions in InGaN compounds with strong compositional fluctuations leading to two distinct types of the regions, one of which is In-rich islands. We assume that optical band-gap within those two regions is randomly fluctuating with Gaussian distribution. Calculated PL spectra as a function of excitation and time are in fair agreement with experimental results demonstrating all the observed peculiarities of luminescence dynamics obtained experimentally.