Time-resolved spectroscopy of InGaN

We have used time-resolved photoluminescence (PL), with 400 nm (3.1 eV) exc itation, to examine InxGa1-xN/GaN light-emitting diodes (LEDs) before the f inal stages of processing at room temperature. We have found dramatic diffe rences in the time-resolved kinetics between dim, bright and super bright L ED devices. The lifetime of the emission for dim LEDs is quite short, 110 /- 20 ps at photoluminescence (PL) maximum and the kinetics are not depende nt upon wavelength. This Lifetime is short compared to bright and super bri ght LEDs, which we have examined under similar conditions. The kinetics of bright and super bright LEDs are clearly wavelength dependent, highly non-e xponential, and are on the nanosecond time scale (lifetimes are in order of 1 ns for bright and 10 ns for super bright LED at the PL max). The nonexpo nential PL kinetics can be described by a stretched exponential function, i ndicating significant disorder in the material. Typical values for beta, th e stretching coefficient, are 0.45 - 0.6 for bright LEDs, at the PL maxima at room temperature. We attribute this disorder to indium alloy fluctuation s. From analysis of the stretched exponential kinetics we estimate the potenti al fluctuations to be approximately 75 meV in the super bright LED. Assumin g a hopping mechanism the average distance between indium quantum dots in t he super bright LED is estimated to be 20 Angstrom.